Cementing & cement evaluation.pdf
Transcript of Cementing & cement evaluation.pdf
7212019 Cementing amp cement evaluationpdf
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Cementing amp cement evaluation
P R E PA R E D B Y A N AC E F
D R I L L I N G I N S T R U C T O R
School of BoumerdesUFR Drilling and Production
ر ا د ا زا ريINSTITUT ALGERIEN DU PETROLE
Contents
Introduction
Types of cementing
Primary cementing
Methods of primary cementing
Primary cementing-casing Designing a cement job
Casing amp cementing accessories
Cementing additives
Remedial cementing
Plug cementing
Squeeze cementing
Cement chemistry and additives
Cement evaluation
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Introduction
A critical Well Construction process used worldwide
Cementing is an important steps in the wellrsquos finishingprocess
Cementing is done by pumping a slurry of cement and water at a strategic point around the casing to bind these up
to the formation
3
Types of cementing
When drilling oil and gas wells several different cementing methodscan be needed
Primary Cementing is the introduction of cementacious materialinto the annulus between casing and open hole
Remedial jobs to repair primary cementing jobs (Squeezecementing Cement plug)
Other cementing plugs for abandonment sidetracking loss zoneshellipetc
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Primary cementing
The placement of a cement slurry into the annulus between the casingand the formation exposed to the wellbore (open hole) or previouscasing
The most important objective of primary cementing is to provide zonalisolation (that is to prevent communications between the differentzones in a well) In addition the cement provides support for theseveral casing strings run in a well
5
Zonal Isolation
Poor Zonal Isolation
improper reservoir evaluation
crossflow of unwanted fluids
corrosion of pipe and scale production
annular pressure and environmental hazards
more than $45 Billionyear spent on unwanted produced water
management
6
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Purpose of primary cementing
Fasten the casing to the formation
Reduce the possibility of blowout from high pressure zones
Protect all Production zones
Prevent fluid movement between different formations or between
formation and the surface
Strengthen and protect casingtubing against corrosion
Support the borehole
7
Methods of primary cementing
Thru-Drill Pipe Cementing (Stab-in)
Outside Cementing (Top Job)
Single stage cementing ( two plugs cementing)
Two Stage Cementing
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Primary Cementing - Casing
Conductor
Surface
Intermediate
Production
Liners
9
Conductor Casing (stove pipe)
Confines circulating fluids
Prevents washing out under rig
Provides elevation for flow nipple and bell nipple
BOP are usually not attached to conductor casings
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Set from 40 to 100 feet
Casing is large 3642 inches inchesdiameter
Hole may be eroded severely
Casing can be pumped out easily and must be tied down
Large excess
Stab-in cementing common Accelerated neat cement
Conductor Casing (stove pipe)
11
Surface casing
Protect water sands
Case unconsolidated formations
Provides primary pressure control
(BOP usually nippled up on surface
casing)
Supports subsequent casings
Case off loss circulation zones
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Itermediate casing
Cases off loss circulation zones water flows etc
Isolates salt sections
Protects open hole from increase in mud weight
Prevents flow from high-pressure zones if mud weight must
be reduced
Basic pressure control casing BOP always installed
Supports subsequent casings
15
Intermediate casing
3000 to 10000 ft (vertical or deviated)
13 38rdquo casing in 16rdquo or 17 frac12rdquo hole
9 58rdquo casing in 12 frac14rdquo hole
Guide shoe or float shoe and float collar commonly used
Cement volumes usually largest in well
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Intermediate casing
Potential problems over-pressured loss zones salt formations
or heaving shales
Narrow pressure window between pore bottom amp frac top
Long casing string may need a two-stage job
Best cementing practices are required
Cemented to surface or to previous casing shoe
Typically filler slurries followed by high compressive tail
Specialized slurries (light heavy salt etc)
17
Production casing
Conduit for Completion String
Provides pressure control
Cover worn or damaged intermediate casing
Setting depth through producing zone
Common sizes 4 12 rdquoand 7 casing
Generally cemented back to intermediate casing
Good cement job is vital to successful completion
Can be a liner
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Production Liner
Isolates the pay zone from other
formations and the fluids in them
Protective housing for production
equipment
usually cemented and perforated
Can be blanked or slotted
Common sizes
3 frac12 4 frac12rdquo 7rsquorsquo
19
Liners
bull Key Points
bull Requires less casing
bull Deeper wells
bull Small annular clearancebull Specialized equipment
Liner WiperPlug
Pump Down Plug
ldquoDartrdquo
Liner Hanger
Previous Shoe
Liner Over Lap
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Methodes of primary cementing
Thru-Drill Pipe Cementing (inner string cementing)
Outside Cementing (Top Job)
Single stage cementing ( two plugs cementing)
Two Stage Cementing
21
Thru-Drill Pipe Cementing (Stab-in)
Key Points
Less cement contamination
Less channelling
Small displacement volume
Pump until cement tosurface
Less job time (rig time)
Less cement
Stingerexe
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Inner string cementing
Operational Sequence for running amp cementing 18 58rdquo
Prepare and measure the 18 58rdquo string (prepare the landing jointaccording to section TD)
Remove the 30 conductor pipe raiser respecting all the time the safety procedures
Run 18 58rdquo casing in the hole circulating from the cellar with a jetpump
Connect last casing joint with the minimum torque
Center the 18 58rdquo string (see figure 1) with metal rig-made slips
Install the IPN in the top of the cellar perpendicular to the 18 58rdquocasing
Install the 18 58rdquo casing elevator between the IPN and the next jointcouple The side door elevator needs to be landing on top of the IPN
Land casing
23
Inner string cementing
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Disconnect landing joint
Check the condition of the ldquoOrdquo rings of the cementing stinger nipple
Use 18 58 X 5 12 DP Centralizer
Run in hole stinger string
Set stinger in casing shoe circulate through the cement stinger andensure the stinger seal is not leaking
RU CMT head RU cementing lines Well Service flush lines with water and test lines to 3000 psi
Have enough cement and additives on location for 100 excess over
required volume Conduct a pump efficiency test and report the results on the daily
drilling report
Inner string cementing
25
Stinger26
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Inner string cementing
27
Cement 18 58rdquo casing pump cement slurries (lead then tail)
While cementing closely monitor any return from DP X Csg annulus
Observe returns from the well for any indication of hole losses orinstability
Displace cement check for mud return
Disconnect stinger from float shoe flush amp POOH the stinger string
Proceed to weld the centralizing slips
Cut 18 58rdquo casing as detailed in the procedures to install casing headhousing
Install casing head housing
Inner string cementing
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Outside Cementing (Top Job)
Key points
Bring cement to surface
Macaroni tubing used
Max depth 250-300 ft
High friction pressures
Non-standard connections
Tubingmovedduring job
29
Single stage cementing ( two plugs cementing)
It is conventional method
The most method used in drilling
Long pumping times
High pump pressures
SingleStageexe
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Two Stage Cementing
The cementing of a string of casing in 02
Stages using a stage collar
1st Stage
StageCollar
33
Why
Potential Casing Collapse due to Hydrostatic Pressure of a full columnof Cement
Lost circulation zone or low Frac gradient
Cement very long intervalle (timevolume limitations)
Reduce use of expensive slurries due to special well problems (saltzone gas zone)
Incomplet fill up (Can leave zone in the annulus uncemented)
Two Stage Cementing
TwoStageexe
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Introduction
A critical Well Construction process used worldwide
Cementing is an important steps in the wellrsquos finishingprocess
Cementing is done by pumping a slurry of cement and water at a strategic point around the casing to bind these up
to the formation
3
Types of cementing
When drilling oil and gas wells several different cementing methodscan be needed
Primary Cementing is the introduction of cementacious materialinto the annulus between casing and open hole
Remedial jobs to repair primary cementing jobs (Squeezecementing Cement plug)
Other cementing plugs for abandonment sidetracking loss zoneshellipetc
4
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Primary cementing
The placement of a cement slurry into the annulus between the casingand the formation exposed to the wellbore (open hole) or previouscasing
The most important objective of primary cementing is to provide zonalisolation (that is to prevent communications between the differentzones in a well) In addition the cement provides support for theseveral casing strings run in a well
5
Zonal Isolation
Poor Zonal Isolation
improper reservoir evaluation
crossflow of unwanted fluids
corrosion of pipe and scale production
annular pressure and environmental hazards
more than $45 Billionyear spent on unwanted produced water
management
6
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Purpose of primary cementing
Fasten the casing to the formation
Reduce the possibility of blowout from high pressure zones
Protect all Production zones
Prevent fluid movement between different formations or between
formation and the surface
Strengthen and protect casingtubing against corrosion
Support the borehole
7
Methods of primary cementing
Thru-Drill Pipe Cementing (Stab-in)
Outside Cementing (Top Job)
Single stage cementing ( two plugs cementing)
Two Stage Cementing
8
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Primary Cementing - Casing
Conductor
Surface
Intermediate
Production
Liners
9
Conductor Casing (stove pipe)
Confines circulating fluids
Prevents washing out under rig
Provides elevation for flow nipple and bell nipple
BOP are usually not attached to conductor casings
10
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Set from 40 to 100 feet
Casing is large 3642 inches inchesdiameter
Hole may be eroded severely
Casing can be pumped out easily and must be tied down
Large excess
Stab-in cementing common Accelerated neat cement
Conductor Casing (stove pipe)
11
Surface casing
Protect water sands
Case unconsolidated formations
Provides primary pressure control
(BOP usually nippled up on surface
casing)
Supports subsequent casings
Case off loss circulation zones
12
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Itermediate casing
Cases off loss circulation zones water flows etc
Isolates salt sections
Protects open hole from increase in mud weight
Prevents flow from high-pressure zones if mud weight must
be reduced
Basic pressure control casing BOP always installed
Supports subsequent casings
15
Intermediate casing
3000 to 10000 ft (vertical or deviated)
13 38rdquo casing in 16rdquo or 17 frac12rdquo hole
9 58rdquo casing in 12 frac14rdquo hole
Guide shoe or float shoe and float collar commonly used
Cement volumes usually largest in well
16
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Intermediate casing
Potential problems over-pressured loss zones salt formations
or heaving shales
Narrow pressure window between pore bottom amp frac top
Long casing string may need a two-stage job
Best cementing practices are required
Cemented to surface or to previous casing shoe
Typically filler slurries followed by high compressive tail
Specialized slurries (light heavy salt etc)
17
Production casing
Conduit for Completion String
Provides pressure control
Cover worn or damaged intermediate casing
Setting depth through producing zone
Common sizes 4 12 rdquoand 7 casing
Generally cemented back to intermediate casing
Good cement job is vital to successful completion
Can be a liner
18
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Production Liner
Isolates the pay zone from other
formations and the fluids in them
Protective housing for production
equipment
usually cemented and perforated
Can be blanked or slotted
Common sizes
3 frac12 4 frac12rdquo 7rsquorsquo
19
Liners
bull Key Points
bull Requires less casing
bull Deeper wells
bull Small annular clearancebull Specialized equipment
Liner WiperPlug
Pump Down Plug
ldquoDartrdquo
Liner Hanger
Previous Shoe
Liner Over Lap
20
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Methodes of primary cementing
Thru-Drill Pipe Cementing (inner string cementing)
Outside Cementing (Top Job)
Single stage cementing ( two plugs cementing)
Two Stage Cementing
21
Thru-Drill Pipe Cementing (Stab-in)
Key Points
Less cement contamination
Less channelling
Small displacement volume
Pump until cement tosurface
Less job time (rig time)
Less cement
Stingerexe
22
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Inner string cementing
Operational Sequence for running amp cementing 18 58rdquo
Prepare and measure the 18 58rdquo string (prepare the landing jointaccording to section TD)
Remove the 30 conductor pipe raiser respecting all the time the safety procedures
Run 18 58rdquo casing in the hole circulating from the cellar with a jetpump
Connect last casing joint with the minimum torque
Center the 18 58rdquo string (see figure 1) with metal rig-made slips
Install the IPN in the top of the cellar perpendicular to the 18 58rdquocasing
Install the 18 58rdquo casing elevator between the IPN and the next jointcouple The side door elevator needs to be landing on top of the IPN
Land casing
23
Inner string cementing
24
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Disconnect landing joint
Check the condition of the ldquoOrdquo rings of the cementing stinger nipple
Use 18 58 X 5 12 DP Centralizer
Run in hole stinger string
Set stinger in casing shoe circulate through the cement stinger andensure the stinger seal is not leaking
RU CMT head RU cementing lines Well Service flush lines with water and test lines to 3000 psi
Have enough cement and additives on location for 100 excess over
required volume Conduct a pump efficiency test and report the results on the daily
drilling report
Inner string cementing
25
Stinger26
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Inner string cementing
27
Cement 18 58rdquo casing pump cement slurries (lead then tail)
While cementing closely monitor any return from DP X Csg annulus
Observe returns from the well for any indication of hole losses orinstability
Displace cement check for mud return
Disconnect stinger from float shoe flush amp POOH the stinger string
Proceed to weld the centralizing slips
Cut 18 58rdquo casing as detailed in the procedures to install casing headhousing
Install casing head housing
Inner string cementing
28
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Outside Cementing (Top Job)
Key points
Bring cement to surface
Macaroni tubing used
Max depth 250-300 ft
High friction pressures
Non-standard connections
Tubingmovedduring job
29
Single stage cementing ( two plugs cementing)
It is conventional method
The most method used in drilling
Long pumping times
High pump pressures
SingleStageexe
30
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Two Stage Cementing
The cementing of a string of casing in 02
Stages using a stage collar
1st Stage
StageCollar
33
Why
Potential Casing Collapse due to Hydrostatic Pressure of a full columnof Cement
Lost circulation zone or low Frac gradient
Cement very long intervalle (timevolume limitations)
Reduce use of expensive slurries due to special well problems (saltzone gas zone)
Incomplet fill up (Can leave zone in the annulus uncemented)
Two Stage Cementing
TwoStageexe
34
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
36
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
38
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Primary cementing
The placement of a cement slurry into the annulus between the casingand the formation exposed to the wellbore (open hole) or previouscasing
The most important objective of primary cementing is to provide zonalisolation (that is to prevent communications between the differentzones in a well) In addition the cement provides support for theseveral casing strings run in a well
5
Zonal Isolation
Poor Zonal Isolation
improper reservoir evaluation
crossflow of unwanted fluids
corrosion of pipe and scale production
annular pressure and environmental hazards
more than $45 Billionyear spent on unwanted produced water
management
6
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Purpose of primary cementing
Fasten the casing to the formation
Reduce the possibility of blowout from high pressure zones
Protect all Production zones
Prevent fluid movement between different formations or between
formation and the surface
Strengthen and protect casingtubing against corrosion
Support the borehole
7
Methods of primary cementing
Thru-Drill Pipe Cementing (Stab-in)
Outside Cementing (Top Job)
Single stage cementing ( two plugs cementing)
Two Stage Cementing
8
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Primary Cementing - Casing
Conductor
Surface
Intermediate
Production
Liners
9
Conductor Casing (stove pipe)
Confines circulating fluids
Prevents washing out under rig
Provides elevation for flow nipple and bell nipple
BOP are usually not attached to conductor casings
10
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Set from 40 to 100 feet
Casing is large 3642 inches inchesdiameter
Hole may be eroded severely
Casing can be pumped out easily and must be tied down
Large excess
Stab-in cementing common Accelerated neat cement
Conductor Casing (stove pipe)
11
Surface casing
Protect water sands
Case unconsolidated formations
Provides primary pressure control
(BOP usually nippled up on surface
casing)
Supports subsequent casings
Case off loss circulation zones
12
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Itermediate casing
Cases off loss circulation zones water flows etc
Isolates salt sections
Protects open hole from increase in mud weight
Prevents flow from high-pressure zones if mud weight must
be reduced
Basic pressure control casing BOP always installed
Supports subsequent casings
15
Intermediate casing
3000 to 10000 ft (vertical or deviated)
13 38rdquo casing in 16rdquo or 17 frac12rdquo hole
9 58rdquo casing in 12 frac14rdquo hole
Guide shoe or float shoe and float collar commonly used
Cement volumes usually largest in well
16
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Intermediate casing
Potential problems over-pressured loss zones salt formations
or heaving shales
Narrow pressure window between pore bottom amp frac top
Long casing string may need a two-stage job
Best cementing practices are required
Cemented to surface or to previous casing shoe
Typically filler slurries followed by high compressive tail
Specialized slurries (light heavy salt etc)
17
Production casing
Conduit for Completion String
Provides pressure control
Cover worn or damaged intermediate casing
Setting depth through producing zone
Common sizes 4 12 rdquoand 7 casing
Generally cemented back to intermediate casing
Good cement job is vital to successful completion
Can be a liner
18
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Production Liner
Isolates the pay zone from other
formations and the fluids in them
Protective housing for production
equipment
usually cemented and perforated
Can be blanked or slotted
Common sizes
3 frac12 4 frac12rdquo 7rsquorsquo
19
Liners
bull Key Points
bull Requires less casing
bull Deeper wells
bull Small annular clearancebull Specialized equipment
Liner WiperPlug
Pump Down Plug
ldquoDartrdquo
Liner Hanger
Previous Shoe
Liner Over Lap
20
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Methodes of primary cementing
Thru-Drill Pipe Cementing (inner string cementing)
Outside Cementing (Top Job)
Single stage cementing ( two plugs cementing)
Two Stage Cementing
21
Thru-Drill Pipe Cementing (Stab-in)
Key Points
Less cement contamination
Less channelling
Small displacement volume
Pump until cement tosurface
Less job time (rig time)
Less cement
Stingerexe
22
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Inner string cementing
Operational Sequence for running amp cementing 18 58rdquo
Prepare and measure the 18 58rdquo string (prepare the landing jointaccording to section TD)
Remove the 30 conductor pipe raiser respecting all the time the safety procedures
Run 18 58rdquo casing in the hole circulating from the cellar with a jetpump
Connect last casing joint with the minimum torque
Center the 18 58rdquo string (see figure 1) with metal rig-made slips
Install the IPN in the top of the cellar perpendicular to the 18 58rdquocasing
Install the 18 58rdquo casing elevator between the IPN and the next jointcouple The side door elevator needs to be landing on top of the IPN
Land casing
23
Inner string cementing
24
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Disconnect landing joint
Check the condition of the ldquoOrdquo rings of the cementing stinger nipple
Use 18 58 X 5 12 DP Centralizer
Run in hole stinger string
Set stinger in casing shoe circulate through the cement stinger andensure the stinger seal is not leaking
RU CMT head RU cementing lines Well Service flush lines with water and test lines to 3000 psi
Have enough cement and additives on location for 100 excess over
required volume Conduct a pump efficiency test and report the results on the daily
drilling report
Inner string cementing
25
Stinger26
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Inner string cementing
27
Cement 18 58rdquo casing pump cement slurries (lead then tail)
While cementing closely monitor any return from DP X Csg annulus
Observe returns from the well for any indication of hole losses orinstability
Displace cement check for mud return
Disconnect stinger from float shoe flush amp POOH the stinger string
Proceed to weld the centralizing slips
Cut 18 58rdquo casing as detailed in the procedures to install casing headhousing
Install casing head housing
Inner string cementing
28
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Outside Cementing (Top Job)
Key points
Bring cement to surface
Macaroni tubing used
Max depth 250-300 ft
High friction pressures
Non-standard connections
Tubingmovedduring job
29
Single stage cementing ( two plugs cementing)
It is conventional method
The most method used in drilling
Long pumping times
High pump pressures
SingleStageexe
30
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Two Stage Cementing
The cementing of a string of casing in 02
Stages using a stage collar
1st Stage
StageCollar
33
Why
Potential Casing Collapse due to Hydrostatic Pressure of a full columnof Cement
Lost circulation zone or low Frac gradient
Cement very long intervalle (timevolume limitations)
Reduce use of expensive slurries due to special well problems (saltzone gas zone)
Incomplet fill up (Can leave zone in the annulus uncemented)
Two Stage Cementing
TwoStageexe
34
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
36
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
38
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
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Purpose of primary cementing
Fasten the casing to the formation
Reduce the possibility of blowout from high pressure zones
Protect all Production zones
Prevent fluid movement between different formations or between
formation and the surface
Strengthen and protect casingtubing against corrosion
Support the borehole
7
Methods of primary cementing
Thru-Drill Pipe Cementing (Stab-in)
Outside Cementing (Top Job)
Single stage cementing ( two plugs cementing)
Two Stage Cementing
8
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Primary Cementing - Casing
Conductor
Surface
Intermediate
Production
Liners
9
Conductor Casing (stove pipe)
Confines circulating fluids
Prevents washing out under rig
Provides elevation for flow nipple and bell nipple
BOP are usually not attached to conductor casings
10
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Set from 40 to 100 feet
Casing is large 3642 inches inchesdiameter
Hole may be eroded severely
Casing can be pumped out easily and must be tied down
Large excess
Stab-in cementing common Accelerated neat cement
Conductor Casing (stove pipe)
11
Surface casing
Protect water sands
Case unconsolidated formations
Provides primary pressure control
(BOP usually nippled up on surface
casing)
Supports subsequent casings
Case off loss circulation zones
12
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Itermediate casing
Cases off loss circulation zones water flows etc
Isolates salt sections
Protects open hole from increase in mud weight
Prevents flow from high-pressure zones if mud weight must
be reduced
Basic pressure control casing BOP always installed
Supports subsequent casings
15
Intermediate casing
3000 to 10000 ft (vertical or deviated)
13 38rdquo casing in 16rdquo or 17 frac12rdquo hole
9 58rdquo casing in 12 frac14rdquo hole
Guide shoe or float shoe and float collar commonly used
Cement volumes usually largest in well
16
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Intermediate casing
Potential problems over-pressured loss zones salt formations
or heaving shales
Narrow pressure window between pore bottom amp frac top
Long casing string may need a two-stage job
Best cementing practices are required
Cemented to surface or to previous casing shoe
Typically filler slurries followed by high compressive tail
Specialized slurries (light heavy salt etc)
17
Production casing
Conduit for Completion String
Provides pressure control
Cover worn or damaged intermediate casing
Setting depth through producing zone
Common sizes 4 12 rdquoand 7 casing
Generally cemented back to intermediate casing
Good cement job is vital to successful completion
Can be a liner
18
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Production Liner
Isolates the pay zone from other
formations and the fluids in them
Protective housing for production
equipment
usually cemented and perforated
Can be blanked or slotted
Common sizes
3 frac12 4 frac12rdquo 7rsquorsquo
19
Liners
bull Key Points
bull Requires less casing
bull Deeper wells
bull Small annular clearancebull Specialized equipment
Liner WiperPlug
Pump Down Plug
ldquoDartrdquo
Liner Hanger
Previous Shoe
Liner Over Lap
20
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Methodes of primary cementing
Thru-Drill Pipe Cementing (inner string cementing)
Outside Cementing (Top Job)
Single stage cementing ( two plugs cementing)
Two Stage Cementing
21
Thru-Drill Pipe Cementing (Stab-in)
Key Points
Less cement contamination
Less channelling
Small displacement volume
Pump until cement tosurface
Less job time (rig time)
Less cement
Stingerexe
22
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Inner string cementing
Operational Sequence for running amp cementing 18 58rdquo
Prepare and measure the 18 58rdquo string (prepare the landing jointaccording to section TD)
Remove the 30 conductor pipe raiser respecting all the time the safety procedures
Run 18 58rdquo casing in the hole circulating from the cellar with a jetpump
Connect last casing joint with the minimum torque
Center the 18 58rdquo string (see figure 1) with metal rig-made slips
Install the IPN in the top of the cellar perpendicular to the 18 58rdquocasing
Install the 18 58rdquo casing elevator between the IPN and the next jointcouple The side door elevator needs to be landing on top of the IPN
Land casing
23
Inner string cementing
24
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Disconnect landing joint
Check the condition of the ldquoOrdquo rings of the cementing stinger nipple
Use 18 58 X 5 12 DP Centralizer
Run in hole stinger string
Set stinger in casing shoe circulate through the cement stinger andensure the stinger seal is not leaking
RU CMT head RU cementing lines Well Service flush lines with water and test lines to 3000 psi
Have enough cement and additives on location for 100 excess over
required volume Conduct a pump efficiency test and report the results on the daily
drilling report
Inner string cementing
25
Stinger26
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Inner string cementing
27
Cement 18 58rdquo casing pump cement slurries (lead then tail)
While cementing closely monitor any return from DP X Csg annulus
Observe returns from the well for any indication of hole losses orinstability
Displace cement check for mud return
Disconnect stinger from float shoe flush amp POOH the stinger string
Proceed to weld the centralizing slips
Cut 18 58rdquo casing as detailed in the procedures to install casing headhousing
Install casing head housing
Inner string cementing
28
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Outside Cementing (Top Job)
Key points
Bring cement to surface
Macaroni tubing used
Max depth 250-300 ft
High friction pressures
Non-standard connections
Tubingmovedduring job
29
Single stage cementing ( two plugs cementing)
It is conventional method
The most method used in drilling
Long pumping times
High pump pressures
SingleStageexe
30
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Two Stage Cementing
The cementing of a string of casing in 02
Stages using a stage collar
1st Stage
StageCollar
33
Why
Potential Casing Collapse due to Hydrostatic Pressure of a full columnof Cement
Lost circulation zone or low Frac gradient
Cement very long intervalle (timevolume limitations)
Reduce use of expensive slurries due to special well problems (saltzone gas zone)
Incomplet fill up (Can leave zone in the annulus uncemented)
Two Stage Cementing
TwoStageexe
34
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
36
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Primary Cementing - Casing
Conductor
Surface
Intermediate
Production
Liners
9
Conductor Casing (stove pipe)
Confines circulating fluids
Prevents washing out under rig
Provides elevation for flow nipple and bell nipple
BOP are usually not attached to conductor casings
10
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Set from 40 to 100 feet
Casing is large 3642 inches inchesdiameter
Hole may be eroded severely
Casing can be pumped out easily and must be tied down
Large excess
Stab-in cementing common Accelerated neat cement
Conductor Casing (stove pipe)
11
Surface casing
Protect water sands
Case unconsolidated formations
Provides primary pressure control
(BOP usually nippled up on surface
casing)
Supports subsequent casings
Case off loss circulation zones
12
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Itermediate casing
Cases off loss circulation zones water flows etc
Isolates salt sections
Protects open hole from increase in mud weight
Prevents flow from high-pressure zones if mud weight must
be reduced
Basic pressure control casing BOP always installed
Supports subsequent casings
15
Intermediate casing
3000 to 10000 ft (vertical or deviated)
13 38rdquo casing in 16rdquo or 17 frac12rdquo hole
9 58rdquo casing in 12 frac14rdquo hole
Guide shoe or float shoe and float collar commonly used
Cement volumes usually largest in well
16
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Intermediate casing
Potential problems over-pressured loss zones salt formations
or heaving shales
Narrow pressure window between pore bottom amp frac top
Long casing string may need a two-stage job
Best cementing practices are required
Cemented to surface or to previous casing shoe
Typically filler slurries followed by high compressive tail
Specialized slurries (light heavy salt etc)
17
Production casing
Conduit for Completion String
Provides pressure control
Cover worn or damaged intermediate casing
Setting depth through producing zone
Common sizes 4 12 rdquoand 7 casing
Generally cemented back to intermediate casing
Good cement job is vital to successful completion
Can be a liner
18
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Production Liner
Isolates the pay zone from other
formations and the fluids in them
Protective housing for production
equipment
usually cemented and perforated
Can be blanked or slotted
Common sizes
3 frac12 4 frac12rdquo 7rsquorsquo
19
Liners
bull Key Points
bull Requires less casing
bull Deeper wells
bull Small annular clearancebull Specialized equipment
Liner WiperPlug
Pump Down Plug
ldquoDartrdquo
Liner Hanger
Previous Shoe
Liner Over Lap
20
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Methodes of primary cementing
Thru-Drill Pipe Cementing (inner string cementing)
Outside Cementing (Top Job)
Single stage cementing ( two plugs cementing)
Two Stage Cementing
21
Thru-Drill Pipe Cementing (Stab-in)
Key Points
Less cement contamination
Less channelling
Small displacement volume
Pump until cement tosurface
Less job time (rig time)
Less cement
Stingerexe
22
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Inner string cementing
Operational Sequence for running amp cementing 18 58rdquo
Prepare and measure the 18 58rdquo string (prepare the landing jointaccording to section TD)
Remove the 30 conductor pipe raiser respecting all the time the safety procedures
Run 18 58rdquo casing in the hole circulating from the cellar with a jetpump
Connect last casing joint with the minimum torque
Center the 18 58rdquo string (see figure 1) with metal rig-made slips
Install the IPN in the top of the cellar perpendicular to the 18 58rdquocasing
Install the 18 58rdquo casing elevator between the IPN and the next jointcouple The side door elevator needs to be landing on top of the IPN
Land casing
23
Inner string cementing
24
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Disconnect landing joint
Check the condition of the ldquoOrdquo rings of the cementing stinger nipple
Use 18 58 X 5 12 DP Centralizer
Run in hole stinger string
Set stinger in casing shoe circulate through the cement stinger andensure the stinger seal is not leaking
RU CMT head RU cementing lines Well Service flush lines with water and test lines to 3000 psi
Have enough cement and additives on location for 100 excess over
required volume Conduct a pump efficiency test and report the results on the daily
drilling report
Inner string cementing
25
Stinger26
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Inner string cementing
27
Cement 18 58rdquo casing pump cement slurries (lead then tail)
While cementing closely monitor any return from DP X Csg annulus
Observe returns from the well for any indication of hole losses orinstability
Displace cement check for mud return
Disconnect stinger from float shoe flush amp POOH the stinger string
Proceed to weld the centralizing slips
Cut 18 58rdquo casing as detailed in the procedures to install casing headhousing
Install casing head housing
Inner string cementing
28
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Outside Cementing (Top Job)
Key points
Bring cement to surface
Macaroni tubing used
Max depth 250-300 ft
High friction pressures
Non-standard connections
Tubingmovedduring job
29
Single stage cementing ( two plugs cementing)
It is conventional method
The most method used in drilling
Long pumping times
High pump pressures
SingleStageexe
30
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Two Stage Cementing
The cementing of a string of casing in 02
Stages using a stage collar
1st Stage
StageCollar
33
Why
Potential Casing Collapse due to Hydrostatic Pressure of a full columnof Cement
Lost circulation zone or low Frac gradient
Cement very long intervalle (timevolume limitations)
Reduce use of expensive slurries due to special well problems (saltzone gas zone)
Incomplet fill up (Can leave zone in the annulus uncemented)
Two Stage Cementing
TwoStageexe
34
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
36
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
38
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
40
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
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Set from 40 to 100 feet
Casing is large 3642 inches inchesdiameter
Hole may be eroded severely
Casing can be pumped out easily and must be tied down
Large excess
Stab-in cementing common Accelerated neat cement
Conductor Casing (stove pipe)
11
Surface casing
Protect water sands
Case unconsolidated formations
Provides primary pressure control
(BOP usually nippled up on surface
casing)
Supports subsequent casings
Case off loss circulation zones
12
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Itermediate casing
Cases off loss circulation zones water flows etc
Isolates salt sections
Protects open hole from increase in mud weight
Prevents flow from high-pressure zones if mud weight must
be reduced
Basic pressure control casing BOP always installed
Supports subsequent casings
15
Intermediate casing
3000 to 10000 ft (vertical or deviated)
13 38rdquo casing in 16rdquo or 17 frac12rdquo hole
9 58rdquo casing in 12 frac14rdquo hole
Guide shoe or float shoe and float collar commonly used
Cement volumes usually largest in well
16
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Intermediate casing
Potential problems over-pressured loss zones salt formations
or heaving shales
Narrow pressure window between pore bottom amp frac top
Long casing string may need a two-stage job
Best cementing practices are required
Cemented to surface or to previous casing shoe
Typically filler slurries followed by high compressive tail
Specialized slurries (light heavy salt etc)
17
Production casing
Conduit for Completion String
Provides pressure control
Cover worn or damaged intermediate casing
Setting depth through producing zone
Common sizes 4 12 rdquoand 7 casing
Generally cemented back to intermediate casing
Good cement job is vital to successful completion
Can be a liner
18
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Production Liner
Isolates the pay zone from other
formations and the fluids in them
Protective housing for production
equipment
usually cemented and perforated
Can be blanked or slotted
Common sizes
3 frac12 4 frac12rdquo 7rsquorsquo
19
Liners
bull Key Points
bull Requires less casing
bull Deeper wells
bull Small annular clearancebull Specialized equipment
Liner WiperPlug
Pump Down Plug
ldquoDartrdquo
Liner Hanger
Previous Shoe
Liner Over Lap
20
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Methodes of primary cementing
Thru-Drill Pipe Cementing (inner string cementing)
Outside Cementing (Top Job)
Single stage cementing ( two plugs cementing)
Two Stage Cementing
21
Thru-Drill Pipe Cementing (Stab-in)
Key Points
Less cement contamination
Less channelling
Small displacement volume
Pump until cement tosurface
Less job time (rig time)
Less cement
Stingerexe
22
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Inner string cementing
Operational Sequence for running amp cementing 18 58rdquo
Prepare and measure the 18 58rdquo string (prepare the landing jointaccording to section TD)
Remove the 30 conductor pipe raiser respecting all the time the safety procedures
Run 18 58rdquo casing in the hole circulating from the cellar with a jetpump
Connect last casing joint with the minimum torque
Center the 18 58rdquo string (see figure 1) with metal rig-made slips
Install the IPN in the top of the cellar perpendicular to the 18 58rdquocasing
Install the 18 58rdquo casing elevator between the IPN and the next jointcouple The side door elevator needs to be landing on top of the IPN
Land casing
23
Inner string cementing
24
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Disconnect landing joint
Check the condition of the ldquoOrdquo rings of the cementing stinger nipple
Use 18 58 X 5 12 DP Centralizer
Run in hole stinger string
Set stinger in casing shoe circulate through the cement stinger andensure the stinger seal is not leaking
RU CMT head RU cementing lines Well Service flush lines with water and test lines to 3000 psi
Have enough cement and additives on location for 100 excess over
required volume Conduct a pump efficiency test and report the results on the daily
drilling report
Inner string cementing
25
Stinger26
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Inner string cementing
27
Cement 18 58rdquo casing pump cement slurries (lead then tail)
While cementing closely monitor any return from DP X Csg annulus
Observe returns from the well for any indication of hole losses orinstability
Displace cement check for mud return
Disconnect stinger from float shoe flush amp POOH the stinger string
Proceed to weld the centralizing slips
Cut 18 58rdquo casing as detailed in the procedures to install casing headhousing
Install casing head housing
Inner string cementing
28
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Outside Cementing (Top Job)
Key points
Bring cement to surface
Macaroni tubing used
Max depth 250-300 ft
High friction pressures
Non-standard connections
Tubingmovedduring job
29
Single stage cementing ( two plugs cementing)
It is conventional method
The most method used in drilling
Long pumping times
High pump pressures
SingleStageexe
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Two Stage Cementing
The cementing of a string of casing in 02
Stages using a stage collar
1st Stage
StageCollar
33
Why
Potential Casing Collapse due to Hydrostatic Pressure of a full columnof Cement
Lost circulation zone or low Frac gradient
Cement very long intervalle (timevolume limitations)
Reduce use of expensive slurries due to special well problems (saltzone gas zone)
Incomplet fill up (Can leave zone in the annulus uncemented)
Two Stage Cementing
TwoStageexe
34
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
36
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
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Itermediate casing
Cases off loss circulation zones water flows etc
Isolates salt sections
Protects open hole from increase in mud weight
Prevents flow from high-pressure zones if mud weight must
be reduced
Basic pressure control casing BOP always installed
Supports subsequent casings
15
Intermediate casing
3000 to 10000 ft (vertical or deviated)
13 38rdquo casing in 16rdquo or 17 frac12rdquo hole
9 58rdquo casing in 12 frac14rdquo hole
Guide shoe or float shoe and float collar commonly used
Cement volumes usually largest in well
16
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Intermediate casing
Potential problems over-pressured loss zones salt formations
or heaving shales
Narrow pressure window between pore bottom amp frac top
Long casing string may need a two-stage job
Best cementing practices are required
Cemented to surface or to previous casing shoe
Typically filler slurries followed by high compressive tail
Specialized slurries (light heavy salt etc)
17
Production casing
Conduit for Completion String
Provides pressure control
Cover worn or damaged intermediate casing
Setting depth through producing zone
Common sizes 4 12 rdquoand 7 casing
Generally cemented back to intermediate casing
Good cement job is vital to successful completion
Can be a liner
18
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Production Liner
Isolates the pay zone from other
formations and the fluids in them
Protective housing for production
equipment
usually cemented and perforated
Can be blanked or slotted
Common sizes
3 frac12 4 frac12rdquo 7rsquorsquo
19
Liners
bull Key Points
bull Requires less casing
bull Deeper wells
bull Small annular clearancebull Specialized equipment
Liner WiperPlug
Pump Down Plug
ldquoDartrdquo
Liner Hanger
Previous Shoe
Liner Over Lap
20
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Methodes of primary cementing
Thru-Drill Pipe Cementing (inner string cementing)
Outside Cementing (Top Job)
Single stage cementing ( two plugs cementing)
Two Stage Cementing
21
Thru-Drill Pipe Cementing (Stab-in)
Key Points
Less cement contamination
Less channelling
Small displacement volume
Pump until cement tosurface
Less job time (rig time)
Less cement
Stingerexe
22
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Inner string cementing
Operational Sequence for running amp cementing 18 58rdquo
Prepare and measure the 18 58rdquo string (prepare the landing jointaccording to section TD)
Remove the 30 conductor pipe raiser respecting all the time the safety procedures
Run 18 58rdquo casing in the hole circulating from the cellar with a jetpump
Connect last casing joint with the minimum torque
Center the 18 58rdquo string (see figure 1) with metal rig-made slips
Install the IPN in the top of the cellar perpendicular to the 18 58rdquocasing
Install the 18 58rdquo casing elevator between the IPN and the next jointcouple The side door elevator needs to be landing on top of the IPN
Land casing
23
Inner string cementing
24
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Disconnect landing joint
Check the condition of the ldquoOrdquo rings of the cementing stinger nipple
Use 18 58 X 5 12 DP Centralizer
Run in hole stinger string
Set stinger in casing shoe circulate through the cement stinger andensure the stinger seal is not leaking
RU CMT head RU cementing lines Well Service flush lines with water and test lines to 3000 psi
Have enough cement and additives on location for 100 excess over
required volume Conduct a pump efficiency test and report the results on the daily
drilling report
Inner string cementing
25
Stinger26
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Inner string cementing
27
Cement 18 58rdquo casing pump cement slurries (lead then tail)
While cementing closely monitor any return from DP X Csg annulus
Observe returns from the well for any indication of hole losses orinstability
Displace cement check for mud return
Disconnect stinger from float shoe flush amp POOH the stinger string
Proceed to weld the centralizing slips
Cut 18 58rdquo casing as detailed in the procedures to install casing headhousing
Install casing head housing
Inner string cementing
28
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Outside Cementing (Top Job)
Key points
Bring cement to surface
Macaroni tubing used
Max depth 250-300 ft
High friction pressures
Non-standard connections
Tubingmovedduring job
29
Single stage cementing ( two plugs cementing)
It is conventional method
The most method used in drilling
Long pumping times
High pump pressures
SingleStageexe
30
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Two Stage Cementing
The cementing of a string of casing in 02
Stages using a stage collar
1st Stage
StageCollar
33
Why
Potential Casing Collapse due to Hydrostatic Pressure of a full columnof Cement
Lost circulation zone or low Frac gradient
Cement very long intervalle (timevolume limitations)
Reduce use of expensive slurries due to special well problems (saltzone gas zone)
Incomplet fill up (Can leave zone in the annulus uncemented)
Two Stage Cementing
TwoStageexe
34
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
36
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
38
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
40
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
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Itermediate casing
Cases off loss circulation zones water flows etc
Isolates salt sections
Protects open hole from increase in mud weight
Prevents flow from high-pressure zones if mud weight must
be reduced
Basic pressure control casing BOP always installed
Supports subsequent casings
15
Intermediate casing
3000 to 10000 ft (vertical or deviated)
13 38rdquo casing in 16rdquo or 17 frac12rdquo hole
9 58rdquo casing in 12 frac14rdquo hole
Guide shoe or float shoe and float collar commonly used
Cement volumes usually largest in well
16
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Intermediate casing
Potential problems over-pressured loss zones salt formations
or heaving shales
Narrow pressure window between pore bottom amp frac top
Long casing string may need a two-stage job
Best cementing practices are required
Cemented to surface or to previous casing shoe
Typically filler slurries followed by high compressive tail
Specialized slurries (light heavy salt etc)
17
Production casing
Conduit for Completion String
Provides pressure control
Cover worn or damaged intermediate casing
Setting depth through producing zone
Common sizes 4 12 rdquoand 7 casing
Generally cemented back to intermediate casing
Good cement job is vital to successful completion
Can be a liner
18
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Production Liner
Isolates the pay zone from other
formations and the fluids in them
Protective housing for production
equipment
usually cemented and perforated
Can be blanked or slotted
Common sizes
3 frac12 4 frac12rdquo 7rsquorsquo
19
Liners
bull Key Points
bull Requires less casing
bull Deeper wells
bull Small annular clearancebull Specialized equipment
Liner WiperPlug
Pump Down Plug
ldquoDartrdquo
Liner Hanger
Previous Shoe
Liner Over Lap
20
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Methodes of primary cementing
Thru-Drill Pipe Cementing (inner string cementing)
Outside Cementing (Top Job)
Single stage cementing ( two plugs cementing)
Two Stage Cementing
21
Thru-Drill Pipe Cementing (Stab-in)
Key Points
Less cement contamination
Less channelling
Small displacement volume
Pump until cement tosurface
Less job time (rig time)
Less cement
Stingerexe
22
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Inner string cementing
Operational Sequence for running amp cementing 18 58rdquo
Prepare and measure the 18 58rdquo string (prepare the landing jointaccording to section TD)
Remove the 30 conductor pipe raiser respecting all the time the safety procedures
Run 18 58rdquo casing in the hole circulating from the cellar with a jetpump
Connect last casing joint with the minimum torque
Center the 18 58rdquo string (see figure 1) with metal rig-made slips
Install the IPN in the top of the cellar perpendicular to the 18 58rdquocasing
Install the 18 58rdquo casing elevator between the IPN and the next jointcouple The side door elevator needs to be landing on top of the IPN
Land casing
23
Inner string cementing
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Disconnect landing joint
Check the condition of the ldquoOrdquo rings of the cementing stinger nipple
Use 18 58 X 5 12 DP Centralizer
Run in hole stinger string
Set stinger in casing shoe circulate through the cement stinger andensure the stinger seal is not leaking
RU CMT head RU cementing lines Well Service flush lines with water and test lines to 3000 psi
Have enough cement and additives on location for 100 excess over
required volume Conduct a pump efficiency test and report the results on the daily
drilling report
Inner string cementing
25
Stinger26
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Inner string cementing
27
Cement 18 58rdquo casing pump cement slurries (lead then tail)
While cementing closely monitor any return from DP X Csg annulus
Observe returns from the well for any indication of hole losses orinstability
Displace cement check for mud return
Disconnect stinger from float shoe flush amp POOH the stinger string
Proceed to weld the centralizing slips
Cut 18 58rdquo casing as detailed in the procedures to install casing headhousing
Install casing head housing
Inner string cementing
28
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Outside Cementing (Top Job)
Key points
Bring cement to surface
Macaroni tubing used
Max depth 250-300 ft
High friction pressures
Non-standard connections
Tubingmovedduring job
29
Single stage cementing ( two plugs cementing)
It is conventional method
The most method used in drilling
Long pumping times
High pump pressures
SingleStageexe
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Two Stage Cementing
The cementing of a string of casing in 02
Stages using a stage collar
1st Stage
StageCollar
33
Why
Potential Casing Collapse due to Hydrostatic Pressure of a full columnof Cement
Lost circulation zone or low Frac gradient
Cement very long intervalle (timevolume limitations)
Reduce use of expensive slurries due to special well problems (saltzone gas zone)
Incomplet fill up (Can leave zone in the annulus uncemented)
Two Stage Cementing
TwoStageexe
34
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
36
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
7212019 Cementing amp cement evaluationpdf
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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983097
Intermediate casing
Potential problems over-pressured loss zones salt formations
or heaving shales
Narrow pressure window between pore bottom amp frac top
Long casing string may need a two-stage job
Best cementing practices are required
Cemented to surface or to previous casing shoe
Typically filler slurries followed by high compressive tail
Specialized slurries (light heavy salt etc)
17
Production casing
Conduit for Completion String
Provides pressure control
Cover worn or damaged intermediate casing
Setting depth through producing zone
Common sizes 4 12 rdquoand 7 casing
Generally cemented back to intermediate casing
Good cement job is vital to successful completion
Can be a liner
18
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Production Liner
Isolates the pay zone from other
formations and the fluids in them
Protective housing for production
equipment
usually cemented and perforated
Can be blanked or slotted
Common sizes
3 frac12 4 frac12rdquo 7rsquorsquo
19
Liners
bull Key Points
bull Requires less casing
bull Deeper wells
bull Small annular clearancebull Specialized equipment
Liner WiperPlug
Pump Down Plug
ldquoDartrdquo
Liner Hanger
Previous Shoe
Liner Over Lap
20
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Methodes of primary cementing
Thru-Drill Pipe Cementing (inner string cementing)
Outside Cementing (Top Job)
Single stage cementing ( two plugs cementing)
Two Stage Cementing
21
Thru-Drill Pipe Cementing (Stab-in)
Key Points
Less cement contamination
Less channelling
Small displacement volume
Pump until cement tosurface
Less job time (rig time)
Less cement
Stingerexe
22
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Inner string cementing
Operational Sequence for running amp cementing 18 58rdquo
Prepare and measure the 18 58rdquo string (prepare the landing jointaccording to section TD)
Remove the 30 conductor pipe raiser respecting all the time the safety procedures
Run 18 58rdquo casing in the hole circulating from the cellar with a jetpump
Connect last casing joint with the minimum torque
Center the 18 58rdquo string (see figure 1) with metal rig-made slips
Install the IPN in the top of the cellar perpendicular to the 18 58rdquocasing
Install the 18 58rdquo casing elevator between the IPN and the next jointcouple The side door elevator needs to be landing on top of the IPN
Land casing
23
Inner string cementing
24
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Disconnect landing joint
Check the condition of the ldquoOrdquo rings of the cementing stinger nipple
Use 18 58 X 5 12 DP Centralizer
Run in hole stinger string
Set stinger in casing shoe circulate through the cement stinger andensure the stinger seal is not leaking
RU CMT head RU cementing lines Well Service flush lines with water and test lines to 3000 psi
Have enough cement and additives on location for 100 excess over
required volume Conduct a pump efficiency test and report the results on the daily
drilling report
Inner string cementing
25
Stinger26
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Inner string cementing
27
Cement 18 58rdquo casing pump cement slurries (lead then tail)
While cementing closely monitor any return from DP X Csg annulus
Observe returns from the well for any indication of hole losses orinstability
Displace cement check for mud return
Disconnect stinger from float shoe flush amp POOH the stinger string
Proceed to weld the centralizing slips
Cut 18 58rdquo casing as detailed in the procedures to install casing headhousing
Install casing head housing
Inner string cementing
28
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Outside Cementing (Top Job)
Key points
Bring cement to surface
Macaroni tubing used
Max depth 250-300 ft
High friction pressures
Non-standard connections
Tubingmovedduring job
29
Single stage cementing ( two plugs cementing)
It is conventional method
The most method used in drilling
Long pumping times
High pump pressures
SingleStageexe
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Two Stage Cementing
The cementing of a string of casing in 02
Stages using a stage collar
1st Stage
StageCollar
33
Why
Potential Casing Collapse due to Hydrostatic Pressure of a full columnof Cement
Lost circulation zone or low Frac gradient
Cement very long intervalle (timevolume limitations)
Reduce use of expensive slurries due to special well problems (saltzone gas zone)
Incomplet fill up (Can leave zone in the annulus uncemented)
Two Stage Cementing
TwoStageexe
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
36
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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983094983096
Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Production Liner
Isolates the pay zone from other
formations and the fluids in them
Protective housing for production
equipment
usually cemented and perforated
Can be blanked or slotted
Common sizes
3 frac12 4 frac12rdquo 7rsquorsquo
19
Liners
bull Key Points
bull Requires less casing
bull Deeper wells
bull Small annular clearancebull Specialized equipment
Liner WiperPlug
Pump Down Plug
ldquoDartrdquo
Liner Hanger
Previous Shoe
Liner Over Lap
20
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Methodes of primary cementing
Thru-Drill Pipe Cementing (inner string cementing)
Outside Cementing (Top Job)
Single stage cementing ( two plugs cementing)
Two Stage Cementing
21
Thru-Drill Pipe Cementing (Stab-in)
Key Points
Less cement contamination
Less channelling
Small displacement volume
Pump until cement tosurface
Less job time (rig time)
Less cement
Stingerexe
22
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Inner string cementing
Operational Sequence for running amp cementing 18 58rdquo
Prepare and measure the 18 58rdquo string (prepare the landing jointaccording to section TD)
Remove the 30 conductor pipe raiser respecting all the time the safety procedures
Run 18 58rdquo casing in the hole circulating from the cellar with a jetpump
Connect last casing joint with the minimum torque
Center the 18 58rdquo string (see figure 1) with metal rig-made slips
Install the IPN in the top of the cellar perpendicular to the 18 58rdquocasing
Install the 18 58rdquo casing elevator between the IPN and the next jointcouple The side door elevator needs to be landing on top of the IPN
Land casing
23
Inner string cementing
24
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Disconnect landing joint
Check the condition of the ldquoOrdquo rings of the cementing stinger nipple
Use 18 58 X 5 12 DP Centralizer
Run in hole stinger string
Set stinger in casing shoe circulate through the cement stinger andensure the stinger seal is not leaking
RU CMT head RU cementing lines Well Service flush lines with water and test lines to 3000 psi
Have enough cement and additives on location for 100 excess over
required volume Conduct a pump efficiency test and report the results on the daily
drilling report
Inner string cementing
25
Stinger26
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Inner string cementing
27
Cement 18 58rdquo casing pump cement slurries (lead then tail)
While cementing closely monitor any return from DP X Csg annulus
Observe returns from the well for any indication of hole losses orinstability
Displace cement check for mud return
Disconnect stinger from float shoe flush amp POOH the stinger string
Proceed to weld the centralizing slips
Cut 18 58rdquo casing as detailed in the procedures to install casing headhousing
Install casing head housing
Inner string cementing
28
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Outside Cementing (Top Job)
Key points
Bring cement to surface
Macaroni tubing used
Max depth 250-300 ft
High friction pressures
Non-standard connections
Tubingmovedduring job
29
Single stage cementing ( two plugs cementing)
It is conventional method
The most method used in drilling
Long pumping times
High pump pressures
SingleStageexe
30
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Two Stage Cementing
The cementing of a string of casing in 02
Stages using a stage collar
1st Stage
StageCollar
33
Why
Potential Casing Collapse due to Hydrostatic Pressure of a full columnof Cement
Lost circulation zone or low Frac gradient
Cement very long intervalle (timevolume limitations)
Reduce use of expensive slurries due to special well problems (saltzone gas zone)
Incomplet fill up (Can leave zone in the annulus uncemented)
Two Stage Cementing
TwoStageexe
34
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
36
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
38
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983090983088
Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
40
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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983094983096
Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Methodes of primary cementing
Thru-Drill Pipe Cementing (inner string cementing)
Outside Cementing (Top Job)
Single stage cementing ( two plugs cementing)
Two Stage Cementing
21
Thru-Drill Pipe Cementing (Stab-in)
Key Points
Less cement contamination
Less channelling
Small displacement volume
Pump until cement tosurface
Less job time (rig time)
Less cement
Stingerexe
22
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Inner string cementing
Operational Sequence for running amp cementing 18 58rdquo
Prepare and measure the 18 58rdquo string (prepare the landing jointaccording to section TD)
Remove the 30 conductor pipe raiser respecting all the time the safety procedures
Run 18 58rdquo casing in the hole circulating from the cellar with a jetpump
Connect last casing joint with the minimum torque
Center the 18 58rdquo string (see figure 1) with metal rig-made slips
Install the IPN in the top of the cellar perpendicular to the 18 58rdquocasing
Install the 18 58rdquo casing elevator between the IPN and the next jointcouple The side door elevator needs to be landing on top of the IPN
Land casing
23
Inner string cementing
24
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Disconnect landing joint
Check the condition of the ldquoOrdquo rings of the cementing stinger nipple
Use 18 58 X 5 12 DP Centralizer
Run in hole stinger string
Set stinger in casing shoe circulate through the cement stinger andensure the stinger seal is not leaking
RU CMT head RU cementing lines Well Service flush lines with water and test lines to 3000 psi
Have enough cement and additives on location for 100 excess over
required volume Conduct a pump efficiency test and report the results on the daily
drilling report
Inner string cementing
25
Stinger26
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Inner string cementing
27
Cement 18 58rdquo casing pump cement slurries (lead then tail)
While cementing closely monitor any return from DP X Csg annulus
Observe returns from the well for any indication of hole losses orinstability
Displace cement check for mud return
Disconnect stinger from float shoe flush amp POOH the stinger string
Proceed to weld the centralizing slips
Cut 18 58rdquo casing as detailed in the procedures to install casing headhousing
Install casing head housing
Inner string cementing
28
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Outside Cementing (Top Job)
Key points
Bring cement to surface
Macaroni tubing used
Max depth 250-300 ft
High friction pressures
Non-standard connections
Tubingmovedduring job
29
Single stage cementing ( two plugs cementing)
It is conventional method
The most method used in drilling
Long pumping times
High pump pressures
SingleStageexe
30
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Two Stage Cementing
The cementing of a string of casing in 02
Stages using a stage collar
1st Stage
StageCollar
33
Why
Potential Casing Collapse due to Hydrostatic Pressure of a full columnof Cement
Lost circulation zone or low Frac gradient
Cement very long intervalle (timevolume limitations)
Reduce use of expensive slurries due to special well problems (saltzone gas zone)
Incomplet fill up (Can leave zone in the annulus uncemented)
Two Stage Cementing
TwoStageexe
34
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
36
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
38
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
40
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Inner string cementing
Operational Sequence for running amp cementing 18 58rdquo
Prepare and measure the 18 58rdquo string (prepare the landing jointaccording to section TD)
Remove the 30 conductor pipe raiser respecting all the time the safety procedures
Run 18 58rdquo casing in the hole circulating from the cellar with a jetpump
Connect last casing joint with the minimum torque
Center the 18 58rdquo string (see figure 1) with metal rig-made slips
Install the IPN in the top of the cellar perpendicular to the 18 58rdquocasing
Install the 18 58rdquo casing elevator between the IPN and the next jointcouple The side door elevator needs to be landing on top of the IPN
Land casing
23
Inner string cementing
24
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Disconnect landing joint
Check the condition of the ldquoOrdquo rings of the cementing stinger nipple
Use 18 58 X 5 12 DP Centralizer
Run in hole stinger string
Set stinger in casing shoe circulate through the cement stinger andensure the stinger seal is not leaking
RU CMT head RU cementing lines Well Service flush lines with water and test lines to 3000 psi
Have enough cement and additives on location for 100 excess over
required volume Conduct a pump efficiency test and report the results on the daily
drilling report
Inner string cementing
25
Stinger26
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Inner string cementing
27
Cement 18 58rdquo casing pump cement slurries (lead then tail)
While cementing closely monitor any return from DP X Csg annulus
Observe returns from the well for any indication of hole losses orinstability
Displace cement check for mud return
Disconnect stinger from float shoe flush amp POOH the stinger string
Proceed to weld the centralizing slips
Cut 18 58rdquo casing as detailed in the procedures to install casing headhousing
Install casing head housing
Inner string cementing
28
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Outside Cementing (Top Job)
Key points
Bring cement to surface
Macaroni tubing used
Max depth 250-300 ft
High friction pressures
Non-standard connections
Tubingmovedduring job
29
Single stage cementing ( two plugs cementing)
It is conventional method
The most method used in drilling
Long pumping times
High pump pressures
SingleStageexe
30
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Two Stage Cementing
The cementing of a string of casing in 02
Stages using a stage collar
1st Stage
StageCollar
33
Why
Potential Casing Collapse due to Hydrostatic Pressure of a full columnof Cement
Lost circulation zone or low Frac gradient
Cement very long intervalle (timevolume limitations)
Reduce use of expensive slurries due to special well problems (saltzone gas zone)
Incomplet fill up (Can leave zone in the annulus uncemented)
Two Stage Cementing
TwoStageexe
34
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
36
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
38
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
40
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Disconnect landing joint
Check the condition of the ldquoOrdquo rings of the cementing stinger nipple
Use 18 58 X 5 12 DP Centralizer
Run in hole stinger string
Set stinger in casing shoe circulate through the cement stinger andensure the stinger seal is not leaking
RU CMT head RU cementing lines Well Service flush lines with water and test lines to 3000 psi
Have enough cement and additives on location for 100 excess over
required volume Conduct a pump efficiency test and report the results on the daily
drilling report
Inner string cementing
25
Stinger26
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Inner string cementing
27
Cement 18 58rdquo casing pump cement slurries (lead then tail)
While cementing closely monitor any return from DP X Csg annulus
Observe returns from the well for any indication of hole losses orinstability
Displace cement check for mud return
Disconnect stinger from float shoe flush amp POOH the stinger string
Proceed to weld the centralizing slips
Cut 18 58rdquo casing as detailed in the procedures to install casing headhousing
Install casing head housing
Inner string cementing
28
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Outside Cementing (Top Job)
Key points
Bring cement to surface
Macaroni tubing used
Max depth 250-300 ft
High friction pressures
Non-standard connections
Tubingmovedduring job
29
Single stage cementing ( two plugs cementing)
It is conventional method
The most method used in drilling
Long pumping times
High pump pressures
SingleStageexe
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Two Stage Cementing
The cementing of a string of casing in 02
Stages using a stage collar
1st Stage
StageCollar
33
Why
Potential Casing Collapse due to Hydrostatic Pressure of a full columnof Cement
Lost circulation zone or low Frac gradient
Cement very long intervalle (timevolume limitations)
Reduce use of expensive slurries due to special well problems (saltzone gas zone)
Incomplet fill up (Can leave zone in the annulus uncemented)
Two Stage Cementing
TwoStageexe
34
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
36
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
38
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
40
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Inner string cementing
27
Cement 18 58rdquo casing pump cement slurries (lead then tail)
While cementing closely monitor any return from DP X Csg annulus
Observe returns from the well for any indication of hole losses orinstability
Displace cement check for mud return
Disconnect stinger from float shoe flush amp POOH the stinger string
Proceed to weld the centralizing slips
Cut 18 58rdquo casing as detailed in the procedures to install casing headhousing
Install casing head housing
Inner string cementing
28
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Outside Cementing (Top Job)
Key points
Bring cement to surface
Macaroni tubing used
Max depth 250-300 ft
High friction pressures
Non-standard connections
Tubingmovedduring job
29
Single stage cementing ( two plugs cementing)
It is conventional method
The most method used in drilling
Long pumping times
High pump pressures
SingleStageexe
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Two Stage Cementing
The cementing of a string of casing in 02
Stages using a stage collar
1st Stage
StageCollar
33
Why
Potential Casing Collapse due to Hydrostatic Pressure of a full columnof Cement
Lost circulation zone or low Frac gradient
Cement very long intervalle (timevolume limitations)
Reduce use of expensive slurries due to special well problems (saltzone gas zone)
Incomplet fill up (Can leave zone in the annulus uncemented)
Two Stage Cementing
TwoStageexe
34
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
36
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
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Outside Cementing (Top Job)
Key points
Bring cement to surface
Macaroni tubing used
Max depth 250-300 ft
High friction pressures
Non-standard connections
Tubingmovedduring job
29
Single stage cementing ( two plugs cementing)
It is conventional method
The most method used in drilling
Long pumping times
High pump pressures
SingleStageexe
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Two Stage Cementing
The cementing of a string of casing in 02
Stages using a stage collar
1st Stage
StageCollar
33
Why
Potential Casing Collapse due to Hydrostatic Pressure of a full columnof Cement
Lost circulation zone or low Frac gradient
Cement very long intervalle (timevolume limitations)
Reduce use of expensive slurries due to special well problems (saltzone gas zone)
Incomplet fill up (Can leave zone in the annulus uncemented)
Two Stage Cementing
TwoStageexe
34
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
38
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
40
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
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Two Stage Cementing
The cementing of a string of casing in 02
Stages using a stage collar
1st Stage
StageCollar
33
Why
Potential Casing Collapse due to Hydrostatic Pressure of a full columnof Cement
Lost circulation zone or low Frac gradient
Cement very long intervalle (timevolume limitations)
Reduce use of expensive slurries due to special well problems (saltzone gas zone)
Incomplet fill up (Can leave zone in the annulus uncemented)
Two Stage Cementing
TwoStageexe
34
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
36
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
38
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
40
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
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Two Stage Cementing
The cementing of a string of casing in 02
Stages using a stage collar
1st Stage
StageCollar
33
Why
Potential Casing Collapse due to Hydrostatic Pressure of a full columnof Cement
Lost circulation zone or low Frac gradient
Cement very long intervalle (timevolume limitations)
Reduce use of expensive slurries due to special well problems (saltzone gas zone)
Incomplet fill up (Can leave zone in the annulus uncemented)
Two Stage Cementing
TwoStageexe
34
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
36
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Hardware
Stage collar
Plugs
bull First stage wiper plug (bottomplug is optional)
bull Opening plugbomp
bull Closing plug
Two Stage Cementing
35
Stage collar
Running in PositionRunning in Position Cementing Position Closed PositionCementing Position Closed Position
SHEARPINS
OPENING
BOMB
OPENING
BOMB
CLOSING
PLUG
36
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
38
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
40
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
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Where to place stage collar
Problematic formations (lost circulation salt zone hellipetc)
Inside previous casing to
bull Avoid jetting effect on the formation while circulatingcement
bull To ensure that if the collar fails to open at least the openhole section is cemented
Two Stage Cementing
37
Some other points
The stage collar is eventually drilled out leaving the samedrift as the rest of the casing
3 stages cementing is the same as 2 stages but with 2 stagecollars
A stage collar is considered to be a weak point in the casing by many clients and so avoid using them
Alternatives use of lightweight slurries (foam cement)
Two Stage Cementing
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
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Pressure test lines
Pump washspacer
Pump slurry
Drop first stage plug
Slowdown when the first stage plug passes the stage collar
Displace bump plug check returns
Drop bomb wait allocated time (rule of Thumb 200ftmin)
Pressure up to open stage collar
Circulate (WOC if required)
Pump washspacer then pump slurry
Drop closing plug
Displace close stage collar
Check for returns
Two Stage Cementing job procedure
39
Two Stage Cementing examples
13 313 3 88rdquordquo 6868 lbft Casinglbft Casing
Top of cement atTop of cement at 24612461 feetfeet
13 313 3 88rdquo shoe atrdquo shoe at 27892789 feetfeet
9 59 5 88rdquo Stage collar atrdquo Stage collar at 4265426533 feetfeet
12 112 1 44rdquo OHrdquo OH
9 59 5 88rdquordquo 53535050 lbft Casinglbft Casing
9 59 5 88rdquo Float collar atrdquo Float collar at 6348634888 feetfeet
9 59 5 88rdquo Shoe atrdquo Shoe at 63986398 feetfeet
44
33
11
22
Calculate
First stage cementand displacement volume
Second stagecement anddisplaced volume
40
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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1 Would you recommend a 2-stage
Why
2 What depth would the Collar be
3 What is the maximum density of
slurry possible during the first stage
(assume cmt to stage collar)
4 Where would the TOC be for the first
stage
Two Stage Cementing examples
Frac Gradient 08 psiftMW = 12 ppg
salt zone salt zone
2400rsquo
5500rsquo
5850rsquo
TD8400rsquo
41
Frac Gradient 08 psiftMW = 112 ppg
Two Stage Cementing examples
weak formation
weak formation
4100rsquo
7100 -7250FG 06 psift
TD10200rsquo
8400 -8450FG068 psift
42
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Liners
Any string of casing whose top is located below thesurface hung inside the previous casing and is run toits setting depth by drill pipe
LINER HANGER
CASING
SHOE
OVERLAP 50 -500 FT
43
Liners
Way liners
Prime reason
Save money (Cost of 1 Joint of Casing can be $3000)
Cover CorrodedDamaged Casing
Cover
bull Lost Circulation Zones
bull Shale or Plastic Formations
bull Salt Zones
Deep Wells Rig Unable to Lift Long String of Casing
44
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Types of liners
Production
bull Most common
bull Save$$
bull Slotted liner
bull Blanked liner
Intermediatedrilling
bull Cover problem zone in order to be able to continue drilling
Tie-backliner complement
bull From top of existing liner to surface or further up casing to covercorroded or damaged zone
45
Types of liners
Tie-Back (Liner Complement)
This is often done if production iscommercially viable or there is damageto casing above the liner
TIE BACK
STINGER WITHSEALS
LINER
46
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Liners47
Procedure for Setting Liner
RIH hole with drill pipe
At liner hanger depth condition mud (Reciprocation Rotation)
Release slips (liner hanger) (Rotation - mechanical pressure -hydraulic)
Set slips release liner weight check to see if running tool is free
Pump mud - to ensure free circulation
Cement Displace Bump plug Bleed off
Release setting tool
POOH above TOC and circulate
48
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Liner cement job procedure
Pressure test lines
Pump washspacer
Pump slurry
Drop Pump Down plug (or drill pipe wiper dart)
Displace
bull To running tool and slow down the rate
bull Shear Wiper Plugldquo
bull Displace to Float Collar Slow down while approaching end ofdisplacement
Bump plugcheckf or returns Release tool
Pull up to TOC and reverse circulate circulate
Linerexe
49
Liner overlap
Cementing the liner lap is critical
Too much cement above the liner hanger is not recommended
So make sure that uncontaminated cement is present at the liner lap -
washes and spacers WELLCLEAN
If not there is communication from the annulus to the formation
50
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Liner exemple well schematic
3 12rdquo drill pipe 133 lbft
9 58rdquo casing shoe at 6500 ft
9 58rdquo casing 47 lbft
7rdquo liner 29 lbft Top at6200 ft
7rdquo liner shoe at 10500 ft
4 12rdquo liner 166 lbft top 10100ft collar 14320 ft
4 12rdquo liner shoe at 14400ft
6rdquo Open hole + 20 Excess
53
Designing a Cement Job
Compute fluid volumes
Slurry
Wash Spacer
displacement volumes based on
Hole capacity
Casing capacity
Annular length
54
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Designing a Cement Job
Check that well security is respected
Simulate cement pumping process to compute hydrostatic anddynamic pressures and compare them to
bull pore pressure
bull Fracture pressure
bull Tubular burst pressure
Ensure well security when Running In Hole
Check Temperature and thickening time
55
Designing a Cement Job
Check for an efficient mud removal to preventmud channeling and to ensure good zonalisolation
bull Optimize fluid properties
bull Optimize the pumping rate
bull Optimize casing centralization
Ensure good wall cleaning
bull Optimize pre-flushes volume and flow rate
56
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
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Parameters required
WELL PARAMETERS FLUID PARAMETERS
Hole size and depthCasing tally PP and FPTemperatureCentralization
Densities
Rheology PV and Ty
Cement additives
57
Cement calculations
Prior to a cement job the following calculations are made
1 Cement volume requirements
2 Cement displacement volume
3 Cement slurry composition calculations
58
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
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The following categories are involved
Cement volume (annular volume)
Amount of water to make the cement
Cement density and yield
Displacement for landing top plug
Pumping pressure for landing top plug
Hydrostatic pressure on the formation
Pressure for casing axial force during pressure test after the top cementplug is bumped
Cement calculations
59
Cement slurry volume
Before a cementing job can be carried out volume calculations areneeded
Depending on the drilling fluid program and types of formation thehole diameter will be somewhat larger than the drill bit diameter
Annular volume is calculated to determine the amount of cement to bemixed
The amount is decided by making calculations based on the drill bitdiameter plus an extra amount based on experience or what is knownabout the formations in that particular area or caliper log
This forms the basis for the cement companys calculation of the totaltime needed for mixing and pumping the required
Cement calculations
60
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Cement slurry volume
After the casing is put into place this calculated amount will normally be adjusted based on data collected via the caliper log
The caliper log does not give completely reliable results and is usuallyused to find out whether the calculated cement volume based on thedrill bit diameter is satisfactory
We normally use between 125 and 2 times the cement volume which was calculated by using drill bit diameter this to compensate for wash-
out in the well
Cement calculations
61
Cement slurry volume
This is especially important with regard to deviation drilling as these wells have a tendency to become oval and so excess cement is needed
This can often vary up to as much as 50 of the calculated hole volume
The ratio of fullness in the annulus will vary somewhat depending onpractice in the different companies and the demands from theauthorities
The two upper casings are always cemented back to the surface
Normal cement volume is 100-200 more than calculated volume based on ideal diameters
12 14 and 8 12 sections often have 30-50 excess
Cement calculations
62
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
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Cement slurry volume
The required volume of cement slurry is based on the following factors
Length of open hole
Diameter of the open hole (drill bit diameter and degree of washout)
External and internal diameter in the particular casing
Top of cement in the well
Cement calculations
63
Cement slurry composition calculations are based on kilos or liters per100 kg cement powder
Slurry composition is characterized by1 Slurry Density
2 Thickening time
3 Ultimate cement strength
4 Slurry permeability
5 Slurry viscosity (Pressure loss)
6 Fluid loss
Cement calculations
64
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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A 7 liner cementation require 43 m3 cement slurry volume
From cementing company laboratory
bull The slurry density is 190 kgliter
bull Slurry yield is 9688 LHK
Additives
bull Micro Block (Gas Block Additive) 18 LHK
bull CFR3L (Thinner) 115 LHK
bull SCR-100L (Retarder) 20 LHK
bullHALAD (Fluid loss reducer) 65 LHK
bull NF-5 ( De-foamer) 01 LHK
bull Fresh Water 3738 LHK
Cement calculations
65
Step 1 Calculate cement requirements
Cernent Requirement = CementVolumex100slurry yield (LHK)
= 43000 x 1009688= 4439 ton
LHK = Litre per Hundred Kilo Cement
Cement calculations
66
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Additive calculations67
A 9 58 casing cement job require 123 m3 cement slurry volumeCalculate cement and mix water and liquid additives per measuringtank
From cementing company laboratory
bull The slurry density is 192 kglitrebull Slurry yield is 9588 LHK
Additives
bull CFR3L (Thinner) 127 LHK
bull SCR-100L (Retarder) 140 LHK
bull HALAD (Fluid loss reducer) 570 LHK
bull NF-5 (De-foamer) 015 LHK
bull Fresh Water 3538 LHK
Additive calculations exercise
68
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Displacement Volume
After the cement is mixed and pumped into the well it isdisplaced down the casing and up the annulus
The displacement volume is the volume needed to send the topplug from the cement head to the float collar
This is normally done by multiplying the length with the capacityfor the string
A pump efficiency is used for these calculations
This capacity varies normally between 96 - 99
Cement calculations
69
Pumping Pressure to Charge Top Plug
When the cement leaves the casing shoe and start to move up in theannulus we will notice the u -tube effect by the heavier slurry in theannulus
Example A casing is cemented with 190 sg slurry and displaced with 1 35 sgTop Of Cement TOC is at 1000 m Cement shoe is at 2000 m and thefloat collar is at 1976 m What is the differential pressure just before thetop plug lands (ignore friction)
AP = (1976 -1000) x 00981 x (190 - 135) = 527 bar
70
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
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Hydrostatic Pressure
To ensure we are not fracturing the formation during the cement job itis necessary to calculate the hydrostatic pressure in the cement slurry to be used
Get an idea of whether there is a risk of the well fracturing when we arecementing
We must calculate pressure at different levels in the well based on thegeological conditions
In very weak zones we must take extra care with regard to friction
pressure in addition to the hydrostatic pressure
71
Casing amp cementing Accessories72
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Guide Shoe
Attached to first length of casing to belowered into hole
Guides casing into borehole andaround obstructions
Can be drilled out with the bit
73
bull Float Collar
ndash This is set about two-three joints above the casing shoe and actas a one way valve
ndash When it is used the cement plugs land on top of it
Ball Type
Flapper Type
Float collar
74
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Wiper Plugs
To Separate Fluids
(cementwashspacermud)
Wiping the casing clean
Surface indication of
placement
Bottom Plug
(pump through)
Top Plug (Solid)
75
Others
Centralizer to centrecasing in bore hole topromote even distributionof cement around casing
Cementing Basket tominimize losses in weakzones
Scratchers to scratch offthe mud cake to improvecement bond
76
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Cement Heads
Conventional cement head
77
Batch MixerDiesel Engine
Bulk PlantSilos WBB Compressor Dust
Collector
Fill
Equipment On-Shore
78
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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LASLiquid Addtive System
Slurry ChiefMixing System
CPSCement Pump Skid
Batch Mixer
Cement Head(Sub Sea System)
Equipment Off-Shore
79
Mixing amp Surface equipment
80
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Mixing amp Surface equipment
81
Casing String Components from bottom up
Float shoeFloat shoendashndash guide and check valve to preventguide and check valve to prevent
cement back flow cement back flow
22 Casing jointsCasing jointsndashndash to capture any contaminated cementto capture any contaminated cement
Float collarFloat collar
CentralizersCentralizers
ScratchersScratchers
CementHead
Drilling Fluid
Cement
Casing
FloatCollar Float Shoe
Centralizer
Ground Level
Rig Floor
Figure 9 Typical cementing equipment
82
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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REMEDIAL CEMENTING
What is remedial cementing
Why do we do it
Plugs Lost circulationKick off
Abandonment
Squeeze Primary cement job repairUnwanted Water ProductionHigh Gas-Oil Ratio (GOR)Casing Splits or LeaksNonproductive or Depleted Zones
84
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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PLUG CEMENTING
Plug Cementing
Purposesbull To side track above a fish or to initiate directional
drillingbull To plug back a zonebull To plug back a well (abandonment or later re-entry)bull To solve a lost-circulation problem during the drilling
phasebull To provide an anchor for OH tests
86
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Side Track and Directional Drilling
Kick Off Point
NEW
HOLE
CEMENTPLUG
Design considerations
bull High compressivestrength typically withhigh density
bull Length should be enoughto kick off
87
Plug Back a Depleted Zone
DepletedZone
Cement
Plug
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authorities
bull Reservoir zones mayrequire additionaladditives
88
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Lost Circulation
ThiefZone
CEMENTPLUGCEMENTPLUG
Design considerations
bull Sufficient length to coverthe thief zone
bull Successive treatments may be required depending onlosses
bull Lower density to minimise
hydrostatic pressure
89
Abandonment
CEMENTPLUG
CEMENTPLUG
CEMENT
PLUG
Design considerations
bull Sufficient length to provide
a long term barrierbull Legal requirements
dictated by authoritiesbull Reservoir zones may
require additionaladditives
90
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Test Anchor
Test String
Zone to be Tested
WeakFormation
CEMENTPLUG
Design considerations
bull Sufficient compressivestrength to withstandpressure testing
bull Reservoir zones mayrequire additional additives
91
Cement Plugs - design
Design criteria
1 Quality
bull Cement hardness
bull Cement weight
bull Cement permeability
2 Time
Cement setting time (Pumping time) The minimum thickening timeshould be the job time plus a safety factor
2 Cement hardening time (ultimate strength) For kick off plugs theultimate setting time should be achieved prior kick off operation
92
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Cement testing should be carried out using samples of theactual materials to be used during the job (samples of mix
water and leadtail slurries)
Calculate the hydrostatic pressures throughout the job andcheck that the formation is never under balanced Weightedspacers or mud must be used to maintain primary wellcontrol at all times
Cement Plugs - design93
Wherever possible run a slim tubing stinger below the mainpipe The minimum stinger length should be the pluglength plus 30m
The natural tendency for cement slurry is to traveldownwards when it leaves the string since the slurry willgenerally be heavier than the drilling fluid
This can be avoided by spotting a viscous pill below theplug setting interval
Cement Plugs ndash string design
94
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Slurry Properties
Density
lighter for Lost Circulation
heavier for Sidetracking
homogeneous - batchmixing
Rheology
higher for Lost Circulation
Optimum (mud removal)
for Sidetracking lower for placement with
Coiled Tubing
Compressive Strength
higher for Sidetracking
less important for LostCirculation
minimum 500 psi for drillout
Thickening Time
enough for placementPOOH amp circulating clean
95
Optimising Cement Plugs - Slurry mixingplacement
1 Pump a spacer ahead of the slurry to give a separation betweenthe drilling mud and the cement slurry
2 Cement slurry should be batch mixed3 A slight under-displacement is required in order to pull a dry
string4 Pump a spacer behind the slurry to give a separation between
the drilling mud and the cement slurry5 Displace at maximum rates6 If possible rotate the string during the slurry placement and
displacement7 Pull back slowly above the plug and circulate out excess cement
At the same time the inside of the drill pipe will be cleaned forcement
8 Do not run back into the cement plug after pulling clear
96
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Reasons for Cement Plug Failures
Lack of hardness (sidetracking)
Poor isolation (plug back abandonment)
Wrong Depth
Not in place due to sinking to the bottom
Not in place due to loss to thief zone
97
Balanced Plug Placement
bull Most commonly usedmethod
bull Set using drill pipe andstinger
98
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Balanced Plug Placement99
Water or other fluid of different density from that hole is run ahead
and behind cement slurry The volume of fluid ahead and behind
slurry is calculated so that height in casing is same as height inside the
string
mud
water
cement
water
mud
h W
Height of plugafter pulling pipe
Height ofplug with
pipe in place
Balanced Plug Placement100
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Procedure
1 Pump required spacer volume
2 Mix and pup required cement volume
3 Pump spacer behind cernent inside stinger
4 Displace with mud
5 POOH above cement plug
6 Circulate
7 POOH
Balanced Plug Placement101
Example
When the cement stinger is pulledabove the plug The last drop ofcement is leaving the stinger
Then the displacement volume is V = Stinger capacity X distance to top
plug
5DP195 -gt 915lpm
V= 915 x 1450 = 13267 Litre mud +50 m Spacer = 457 litre
Total displacement volume 13724litre
Balanced Plug Placement102
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Exercise
Set 200m balanced cement plug inside 12 14 hole
Use 3 frac12rdquo 133 Ibsft DP cap 386 lpm
50 m spacer between DP and open hole
Bottom of plug at 3000 m
Calculate
1 Required plug cement volume2 Spacer volumes ahead and behind
3 Displacement volume
Balanced Plug Placement103
Question
If the mud density is greater than the cement density
should you over displace or under displace
Balanced Plug Placement
104
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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983090983094983087983088983094983087983090983088983089983091
983093983094
Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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983090983094983087983088983094983087983090983088983089983091
983094983094
At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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983095983090
Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Squeeze Cementing - Applications
bull Primary cement job repair
bull Unwanted Water Production
bull High Gas-Oil Ratio (GOR)
bull Casing Splits or Leaks
bull Non-productive or Depleted Zones
107
Squeeze Cementing - Methods
Squeeze techniques High pressure - above formation frac pressure
Low pressure - below formation frac pressure
Pumping techniques Hesitation
Running
Placement techniques PackerCement Retainer
Bradenhead
Coiled tubing
108
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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983090983094983087983088983094983087983090983088983089983091
983095983090
Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
7212019 Cementing amp cement evaluationpdf
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983090983094983087983088983094983087983090983088983089983091
983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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983090983094983087983088983094983087983090983088983089983091
983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Low Pressure Squeeze
Squeeze pressure below fracture pressure
Best way to squeeze the pay zone
Use small volume of slurry
Applicable for
Multiple zones
Long intervals
Low BHP wells
Naturally fractured formations
109
High Pressure Squeeze
Fracturing is necessary to place cement in the void
Requires placement of large volumes of slurry
Wash or acid ahead to minimize pump rates required toinitiate fracture
110
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Running Squeeze
Continuous pumping until final squeeze pressure is attained
Clean fluid in the hole
Large slurry volumes without fluid loss control
Low or high pressure squeeze
Applications
Water flow
Abandon perforations
Increase cement top
Casing shoes
Liner tops
Block squeeze
Lost circulation zones
111
Hesitation Squeeze
Intermittent pumping
Low pump rates
Small slurry volumes
Long job times Applications
Channel repair
Long perforated interval
Long splits in casing
Lost circulation
112
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 5784
983090983094983087983088983094983087983090983088983089983091
983093983095
Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
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983090983094983087983088983094983087983090983088983089983091
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Bradenhead Squeeze
Done through tubing or drillpipe without packer
Advantages
No tools are used (simplicity)
Cost
Disadvantages
Casing and wellhead areexposed to pressure
BRIDGE
PLUG
Sand
CEMEN
T
BO
P
113
Packer with Tailpipe Squeeze
bull Downhole Isolation tool
bull Casing and wellheadprotection
bull Tailpipe for placementor setting a bridge plug
bull Long intervals
Packer
CEMENT
Tail Pipe
114
7212019 Cementing amp cement evaluationpdf
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983090983094983087983088983094983087983090983088983089983091
983093983096
Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
7212019 Cementing amp cement evaluationpdf
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983090983094983087983088983094983087983090983088983089983091
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
7212019 Cementing amp cement evaluationpdf
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983090983094983087983088983094983087983090983088983089983091
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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983094983093
Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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983090983094983087983088983094983087983090983088983089983091
983094983094
At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6784
983090983094983087983088983094983087983090983088983089983091
983094983095
A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6884
983090983094983087983088983094983087983090983088983089983091
983094983096
Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6984
983090983094983087983088983094983087983090983088983089983091
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
7212019 Cementing amp cement evaluationpdf
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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983095983090
Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Cement Retainer Squeeze
Drillable Isolation Tool
Similar to packer withouttailpipe
Applications
Squeeze pressure trapped
BRIDGE PLUG
Sand
CEMENT
CEMENT
RETAINER
115
Coiled Tubing Squeeze
Applications Producing wells
Through tubing
Advantages Cost
Accurate placement
116
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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983095983090
Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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983090983094983087983088983094983087983090983088983089983091
983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
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A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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Cement Chemistry amp Additives
Cement is made of Limestone and clay or shale mixed inthe right proportions
Each run may be slightly different due to impurities
Cement is heated in a rotary kiln from 2600 to 2800degrees F
What comes out of the kiln is called clinker
The Clinker and Its Components118
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
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Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
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Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
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Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
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CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
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CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
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Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
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Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
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Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
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983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
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Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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The Clinker and Its Components
The clinker is the mixture formed by the clinkering processThe clinker has four components C3S C2S C3A and C4AF
The letters in the clinker names are not chemical formulasInstead the letters represent abbreviations of chemicalformulas
C ndash CaO
S ndash SiO2
A ndash Al2O3 F ndash Fe2O3
119
Clinker Scientific Name ChemicalFormula
Properties in Cement
C3S Tricalcium silicate 3CaO SiO2 Major component (50 to60)
Strength development
C2S Dicalcium silicate 2CaO SiO2 Final compressivestrength
C3A Tricalciumaluminate
3CaO AlO3 Sets rapidly Controlled by gypsumEarly strengthdevelopment
C4AF Tetracalciumaluminoferrite
4CaO Al2O3 Fe2O3 Little influence
The Clinker and Its Components120
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Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
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983090983094983087983088983094983087983090983088983089983091
983094983091
Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
7212019 Cementing amp cement evaluationpdf
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983094983092
Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
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Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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983094983095
A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
7212019 Cementing amp cement evaluationpdf
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983090983094983087983088983094983087983090983088983089983091
983094983096
Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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983090983094983087983088983094983087983090983088983089983091
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Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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983090983094983087983088983094983087983090983088983089983091
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
7212019 Cementing amp cement evaluationpdf
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983090983094983087983088983094983087983090983088983089983091
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7284
983090983094983087983088983094983087983090983088983089983091
983095983090
Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
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983095983091
Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7484
983090983094983087983088983094983087983090983088983089983091
983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7584
983090983094983087983088983094983087983090983088983089983091
983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7684
983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
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983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
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983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
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7212019 Cementing amp cement evaluationpdf
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983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
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983094983089
Portland Cement
After the clinker is formed and cooled it is moved to a second grindingmill where it is combined with 15 to 5 gypsum (CaSO4 2H2O) by weight of clinker When added in this amount (generally +- 3)gypsum prevents flash set by controlling the hydration of C3A
If more than 5 gypsum is added to the clinker the cement undergoesa false set Excess gypsum causes false set because it tends to hydratequicker than the cement The clinker and gypsum mixture is groundand blended to form Portland cement
Cement reactivity to water depends a lot on surface area which isrelated to the size of the cement grains Cement grain size ranges from 1to 100 microns (average size around 30 microns)
121
API Cement Classes
122
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983094983090
API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
7212019 Cementing amp cement evaluationpdf
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983090983094983087983088983094983087983090983088983089983091
983094983091
Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6484
983090983094983087983088983094983087983090983088983089983091
983094983092
Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
7212019 Cementing amp cement evaluationpdf
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983094983093
Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
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983094983094
At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
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983090983094983087983088983094983087983090983088983089983091
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A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
7212019 Cementing amp cement evaluationpdf
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983094983096
Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
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983090983094983087983088983094983087983090983088983089983091
983094983097
Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
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Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
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Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
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983095983090
Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
7212019 Cementing amp cement evaluationpdf
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983090983094983087983088983094983087983090983088983089983091
983095983091
Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7484
983090983094983087983088983094983087983090983088983089983091
983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7584
983090983094983087983088983094983087983090983088983089983091
983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7684
983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6284
983090983094983087983088983094983087983090983088983089983091
983094983090
API Cement Classes
123
Cement must be placed in wells ranging from shallow to very deep
Additives are used to adjust cement properties and tailorthe cement to specific needs
Cement Additives
124
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6384
983090983094983087983088983094983087983090983088983089983091
983094983091
Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6484
983090983094983087983088983094983087983090983088983089983091
983094983092
Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6584
983090983094983087983088983094983087983090983088983089983091
983094983093
Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6684
983090983094983087983088983094983087983090983088983089983091
983094983094
At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6784
983090983094983087983088983094983087983090983088983089983091
983094983095
A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6884
983090983094983087983088983094983087983090983088983089983091
983094983096
Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6984
983090983094983087983088983094983087983090983088983089983091
983094983097
Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7084
983090983094983087983088983094983087983090983088983089983091
983095983088
Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7184
983090983094983087983088983094983087983090983088983089983091
983095983089
Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7284
983090983094983087983088983094983087983090983088983089983091
983095983090
Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7384
983090983094983087983088983094983087983090983088983089983091
983095983091
Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7484
983090983094983087983088983094983087983090983088983089983091
983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7584
983090983094983087983088983094983087983090983088983089983091
983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7684
983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6384
983090983094983087983088983094983087983090983088983089983091
983094983091
Extenders
Lightweight additives or extenders are used to decreasethe density of cement
Excess mix water can be used to decrease the density toa limited extent
Excess water increases thickening time increases free
water and reduces compressive strength
Cement Additives
125
Extenders
bull Bentonite is the most common light weight additive
bull Bentonite will tie up extra mix water reducing density bull Light weight cements have as much as 12 bentonite
bull Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
Cement Additives
126
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6484
983090983094983087983088983094983087983090983088983089983091
983094983092
Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6584
983090983094983087983088983094983087983090983088983089983091
983094983093
Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6684
983090983094983087983088983094983087983090983088983089983091
983094983094
At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6784
983090983094983087983088983094983087983090983088983089983091
983094983095
A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6884
983090983094983087983088983094983087983090983088983089983091
983094983096
Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6984
983090983094983087983088983094983087983090983088983089983091
983094983097
Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7084
983090983094983087983088983094983087983090983088983089983091
983095983088
Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7184
983090983094983087983088983094983087983090983088983089983091
983095983089
Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7284
983090983094983087983088983094983087983090983088983089983091
983095983090
Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7384
983090983094983087983088983094983087983090983088983089983091
983095983091
Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7484
983090983094983087983088983094983087983090983088983089983091
983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7584
983090983094983087983088983094983087983090983088983089983091
983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7684
983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6484
983090983094983087983088983094983087983090983088983089983091
983094983092
Perlite is volcanic glass bubbles that has some times beenused in geothermal wells because of its insulatingproperties
Perlite is considerably more expensive
Gilsonite and kolite are used to reduce density howevertheir primary function is as a lost circulation material
Gilsonite is a black asphalt
Kolite is crushed coal
Extenders
Cement Additives
127
Foamed cements are also used to reduce the density of the
slurry In a foamed cement nitrogen is added to the cement
mixture
Very low densities can be obtained with foamed cement butthey are more expensive
Extenders
Cement Additives
128
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6584
983090983094983087983088983094983087983090983088983089983091
983094983093
Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6684
983090983094983087983088983094983087983090983088983089983091
983094983094
At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6784
983090983094983087983088983094983087983090983088983089983091
983094983095
A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6884
983090983094983087983088983094983087983090983088983089983091
983094983096
Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6984
983090983094983087983088983094983087983090983088983089983091
983094983097
Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7084
983090983094983087983088983094983087983090983088983089983091
983095983088
Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7184
983090983094983087983088983094983087983090983088983089983091
983095983089
Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7284
983090983094983087983088983094983087983090983088983089983091
983095983090
Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7384
983090983094983087983088983094983087983090983088983089983091
983095983091
Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7484
983090983094983087983088983094983087983090983088983089983091
983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7584
983090983094983087983088983094983087983090983088983089983091
983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7684
983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6584
983090983094983087983088983094983087983090983088983089983091
983094983093
Weighting Agents
Hematite is one of the more common additive for highdensity cement due to its high specific gravity
For smaller increases in density barite can be used
Barite is ground fine and requires more mix water to keepthe slurry pumpable
Sand can be added to increase the density due to low mix
water requirements
Cement Additives
129
Densified slurries can be used up to 175 ppg
A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump
Salt can be used to increase the density of a slurry
Salt increases the density of the liquid phase
Cement Additives
130
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6684
983090983094983087983088983094983087983090983088983089983091
983094983094
At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6784
983090983094983087983088983094983087983090983088983089983091
983094983095
A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6884
983090983094983087983088983094983087983090983088983089983091
983094983096
Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6984
983090983094983087983088983094983087983090983088983089983091
983094983097
Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7084
983090983094983087983088983094983087983090983088983089983091
983095983088
Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7184
983090983094983087983088983094983087983090983088983089983091
983095983089
Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7284
983090983094983087983088983094983087983090983088983089983091
983095983090
Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7384
983090983094983087983088983094983087983090983088983089983091
983095983091
Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7484
983090983094983087983088983094983087983090983088983089983091
983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7584
983090983094983087983088983094983087983090983088983089983091
983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7684
983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6684
983090983094983087983088983094983087983090983088983089983091
983094983094
At low temperatures it would
take too long for the cement
to set up so accelerators
are added to the cement
Decrease the thickening time
of cement for shallow low
temperature applications
Cement Additives
131
As a rule of thumbaccelerators areinorganiccompounds
Calcium chloride is the most common accelerator
It is used in concentrations from 1 to 3
Cement Additives
132
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6784
983090983094983087983088983094983087983090983088983089983091
983094983095
A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6884
983090983094983087983088983094983087983090983088983089983091
983094983096
Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6984
983090983094983087983088983094983087983090983088983089983091
983094983097
Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7084
983090983094983087983088983094983087983090983088983089983091
983095983088
Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7184
983090983094983087983088983094983087983090983088983089983091
983095983089
Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7284
983090983094983087983088983094983087983090983088983089983091
983095983090
Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7384
983090983094983087983088983094983087983090983088983089983091
983095983091
Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7484
983090983094983087983088983094983087983090983088983089983091
983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7584
983090983094983087983088983094983087983090983088983089983091
983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7684
983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6784
983090983094983087983088983094983087983090983088983089983091
983094983095
A little salt willaccelerate
A lot of salt willretard thecement
Cement Additives
133
Retarders
Increase the thickening time of cement for deeper hotterapplications
Typically retarders are organic compounds
Cement Additives
134
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6884
983090983094983087983088983094983087983090983088983089983091
983094983096
Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6984
983090983094983087983088983094983087983090983088983089983091
983094983097
Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7084
983090983094983087983088983094983087983090983088983089983091
983095983088
Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7184
983090983094983087983088983094983087983090983088983089983091
983095983089
Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7284
983090983094983087983088983094983087983090983088983089983091
983095983090
Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7384
983090983094983087983088983094983087983090983088983089983091
983095983091
Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7484
983090983094983087983088983094983087983090983088983089983091
983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7584
983090983094983087983088983094983087983090983088983089983091
983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7684
983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6884
983090983094983087983088983094983087983090983088983089983091
983094983096
Retarders
One of the most common retarders is calciumlignosufonate
Sodium Chloride is a retarder at high concentrations
As bottomhole temperatures change the type of
retarder will change
Cement Additives
135
Friction loss additives (Dispersants) are used tothin the cement slurry
bull Organic acids
bull Lignosulfonate
bull Alky aryl sulfonate
bull Phosphate
bull Salt
Cement Additives
136
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6984
983090983094983087983088983094983087983090983088983089983091
983094983097
Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7084
983090983094983087983088983094983087983090983088983089983091
983095983088
Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7184
983090983094983087983088983094983087983090983088983089983091
983095983089
Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7284
983090983094983087983088983094983087983090983088983089983091
983095983090
Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7384
983090983094983087983088983094983087983090983088983089983091
983095983091
Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7484
983090983094983087983088983094983087983090983088983089983091
983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7584
983090983094983087983088983094983087983090983088983089983091
983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7684
983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 6984
983090983094983087983088983094983087983090983088983089983091
983094983097
Lost circulation material
bull Granular material such as gilsonite kolite perlite and walnut hulls
bull Organic compounds canretard the cement
Cement Additives
137
Other Additives
Antifoam defoamer agents
Bonding agents
Gas migration control additives etc
Fluid Loss Control
138
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7084
983090983094983087983088983094983087983090983088983089983091
983095983088
Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7184
983090983094983087983088983094983087983090983088983089983091
983095983089
Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7284
983090983094983087983088983094983087983090983088983089983091
983095983090
Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7384
983090983094983087983088983094983087983090983088983089983091
983095983091
Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7484
983090983094983087983088983094983087983090983088983089983091
983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7584
983090983094983087983088983094983087983090983088983089983091
983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7684
983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7084
983090983094983087983088983094983087983090983088983089983091
983095983088
Cement Evaluation
139
Cement evaluation
Cement bond logs are used to
bull Determine hydraulic isolation between zones of
interestbull Locate cement top
bull Determine feasibility of a cement squeeze
bull Evaluate the quality of the cement
140
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7184
983090983094983087983088983094983087983090983088983089983091
983095983089
Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7284
983090983094983087983088983094983087983090983088983089983091
983095983090
Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7384
983090983094983087983088983094983087983090983088983089983091
983095983091
Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7484
983090983094983087983088983094983087983090983088983089983091
983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7584
983090983094983087983088983094983087983090983088983089983091
983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7684
983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7184
983090983094983087983088983094983087983090983088983089983091
983095983089
Pipe to Cement Bond
Directly related to surface finish of the pipe
A clean surface greatly enhances the bond potentialie no
grease oil spots or paint on the pipe exterior
The pipe to cement bond was formerly the top priority Today
the cement to formation is now considered more critical
Cement evaluation
141
Cement to Formation Bond
Generally determines whether there will be gas or liquid
communication in the annulus
Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake
Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions
Cement evaluation
142
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7284
983090983094983087983088983094983087983090983088983089983091
983095983090
Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7384
983090983094983087983088983094983087983090983088983089983091
983095983091
Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7484
983090983094983087983088983094983087983090983088983089983091
983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7584
983090983094983087983088983094983087983090983088983089983091
983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7684
983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7284
983090983094983087983088983094983087983090983088983089983091
983095983090
Two types of cement evaluation tools
The Sonic Tools
The Cement Bond Log
The Radial Bond Tool
The Ultrasonic Tools
The Circumferential Acoustic ScanningTools
Cement evaluation
143
Acoustic Bond Logs
Acoustic cement bond logs do not directly measure hydraulic seal
Instead they measure the loss of acoustic energy as it propagates
through casing
This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement
144
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7384
983090983094983087983088983094983087983090983088983089983091
983095983091
Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7484
983090983094983087983088983094983087983090983088983089983091
983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7584
983090983094983087983088983094983087983090983088983089983091
983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7684
983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7384
983090983094983087983088983094983087983090983088983089983091
983095983091
Travel Time (Transit Time)
For free-pipe the travel time should match the expected time for thatcasing size
For bonded pipe the travel time should increase as it triggers laterarrivals
If the travel time decreases below casing arrival time and theamplitude drops then suspect eccentralization
If the travel time decreases below casing arrival time and theamplitude increases suspect fast formations
The travel time difference between the 3ft and 5ft receivers should be114 micros If it less than this suspect fast formations
145
Amplitude
For bonded pipe the amplitude should be low
For free-pipe the amplitude will be high
If the amplitude is intermediate cross check with the cement
map to see if itrsquos due to cement channeling or low
compressive strength cement
146
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7484
983090983094983087983088983094983087983090983088983089983091
983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7584
983090983094983087983088983094983087983090983088983089983091
983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7684
983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7484
983090983094983087983088983094983087983090983088983089983091
983095983092
Decentralized Tools String
Centring of the Tool is critical for valid measurements
If the tool is eccentered there are 2 paths for the sonicsignal to take
the travel time will be less than the expected travel timeand the amplitude will be low which will falsely indicategood bonding
147
CBL Tool
Advantage
Widely Used Method to Evaluate the Cement Job
Used to Evaluate the Zonal Isolation Bonding to Casing Bonding toFormation and Cement Compressive Strength
Tool Response Characterized and Well Documented
148
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7584
983090983094983087983088983094983087983090983088983089983091
983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7684
983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7584
983090983094983087983088983094983087983090983088983089983091
983095983093
CBL Tool
CementFormation Casing
TRANS-MITTER
3 FTRECEIVER
5 FT
RECEIVER
A B
C
DE
F
G
149
CBL Log
Free Pipe
Partial Bond
Good Bond
150
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7684
983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7684
983090983094983087983088983094983087983090983088983089983091
983095983094
CBL Tool
Disadvantage
Affected by tool centralization fluid attenuation pressure andtemperature
Affected by fast formations thin cement sheath
Gives only qualitative cement-formation bonding information
Omni-directional signal- Assumes uniform distribution of cementin the annulus
Cannot evaluate the radial placement of cement materials in thecasing formation annulus
Does not provide positive channel identification
151
Sector Tool (Radial Bond Tool)
Measures the quality of the cement bond laterally aroundthe circumference of the casing
It has a single omni-directional transmitter
The 3 foot near spaced receiver is divided into 8 radial
segments measure 45deg increments to produce cementmap for channel identification
The receiver located at 5 feet is the traditional
omni-directional sensing
The amplitude of the received acoustic signal in
each of the segments represents radial
variations in material in the casing-formation
annulus These radial variations in the signal amplitude
could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft Receiveramp 8 Radials
5 Ft Receiver
152
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7784
983090983094983087983088983094983087983090983088983089983091
983095983095
Advantages
Less affected by heavy drill fluids Can log in 18 ppg mud
Not affected by oil based mud
Identifies channels
Not affected by casing thickness Good in wells with corrosion
Centralized very easily in deviated wells up to 60deg
Sector Tool (Radial Bond Tool)153
Disadvantages
Three foot spacing will be affected by fast formation arrivals
Reads incorrect amplitudes in presence of micro annulus( unless rununder pressure)
The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels
Sector Tool (Radial Bond Tool)154
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7884
983090983094983087983088983094983087983090983088983089983091
983095983096
Ultrasonic Tools
Use a single rotating transducer combinedtransmitter and receiver
Acquire ultrasonic waveform data for both cementevaluation and casing evaluation in the samelogging run or pass
The sampling rate of the rotating transducer canprovide 100 azimuthal coverage of the casing
Allows to distinguish cement liquid and gas in thecasing-formation annular space based on theacoustic properties of the received waves
155
Ultrasonic transducer is located 125rdquo to25rdquo from the casing wall
Sends a beam of ultrasonic energy in the500 kHz band
Ultrasonic energy causes the casing to vibrate or ldquoringrdquo
Frequency and decay rate of returnsignal is measured
Casing thickness and impedance ofcement sheath is calculated
By measuring the energy of the vibrationthe presence or absence of cement can bedetected
Ultrasonic Tools
156
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 7984
983090983094983087983088983094983087983090983088983089983091
983095983097
Ultrasonic Theory of Measurement
Ultrasonic transducer acts as transmitter amp receiver
bull Transmits short pulse of acoustic energy
bull Receives multiple echoes from the casing cement amp formation
Casing Resonates
Casing resonance dampened in the presence of cement
Mud Casing Cement FormationTransducer
157
Acoustic Impedance
The Impedance of a material defines the sound properties for thatmaterial It is a product of the density of the medium and the velocityof sound of the medium
Z= p x c
bull Where Z = Impedance in MRaylsbull P = the density in kgm3
bull C = speed of sound in ms
bull Example Z water = 1000 kgm3 1500 msec = 15 MRayls
bull At any bed boundary (Z1 Z2) with different Impedances soundenergy will be reflected and refracted
bull Acoustic impedance of steel Z steel = 45 MRayls
158
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8084
983090983094983087983088983094983087983090983088983089983091
983096983088
Ultrasonic Technique
The amplitude of the signal is proportional to the acousticimpedance of the material behind pipe
Color Acoustic Impedance Material Behind Casing
White 000-038 Gas
Light Blue - Dark Blue 039-230 Liquid Gas - Fresh Water
Yellow - Light Brown 231-270 Heavy Drilling Fluid ndash Light Cement
Light Brown - Dark Brown 271-385 Low Impedance Cement
Dark Brown 386-500 Medium Impedance Cement
Black gt 500 High Impedance Cement
159
White color = Z lt 14 MraylsBlue color = 14ltZlt18 Mrayls
Yellow color = Zgt18 Mrayls
Acoustic Impedance Map
160
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8184
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8284
983090983094983087983088983094983087983090983088983089983091
983096983090
Channel in the cement
Micro-annulus
Fast formations
Cement Evaluation-Difficulties
163
Cement channels are longitudinal pockets with no cement
May happen when the mud is not adequately flushed from the wellbore during thecementing process (accentuated when the casing is not centralized)
Channeling could be caused by gas or water migration during the time that thecement is curing and or in high angle wells where heavy cement sinks to the lowside of the wellbore leaving little or no cement on the high side
Channel in the cement
164
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8384
983090983094983087983088983094983087983090983088983089983091
983096983091
A micro annulus is a microscopic gap between thecement and the casing which causes poor acousticcoupling
The gap has been estimated in the range of 0005-001rdquo (012 to 025 mm)
A micro annulus does not compromise hydraulicisolation
Log indicates moderate casing amplitude andformation arrivals
Indicates poor bond when good hydraulicisolation is present
If a micro annulus is suspected re-run the log withthe casing under pressure (500 to 1000 psi)
Micro-annulus
165
Pressure differential placed on casingbull Pressure on a cement plug
bull Pressure testing casing
bull
Stimulation (acidizing fracturing etc) Different hydrostatic pressures on casing
bull Change of wellbore fluids while cement is curing
Mechanicalbull Moving pipe after cementing etc
Thermal Micro-annulusbull Heat generated by curing cement
Micro-annulus
166
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168
7212019 Cementing amp cement evaluationpdf
httpslidepdfcomreaderfullcementing-cement-evaluationpdf 8484
983090983094983087983088983094983087983090983088983089983091
Fast formations
bull A Fast formation is a formation where the sonic velocity is higher orfaster than the sonic velocity in casing
bull Formation signals can arrive at the 3ft receiver before the casing signal
bull Formation signal arrives in the amplitude gate resulting ininterpretation as poor bond
bull As a check the travel time to the first arrival should be examinedbull Indications on the log are increased amplitude and decreased Travel
Time
167
168