Sonatrach Cementing

Development Phase

September October 2005abalt solutions limited - 2005

INTRODUCTION TO HYDROCARBON EXPLOITATION

Abalt Solutions

Introduction to Hydrocarbon Exploitation

2005 Abalt Solutions Limited. All rights reserved

Development Phase

CementingBy Pratap Thimaiah

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Cementing

It is the process by which cement slurry isplaced in the annulus ,bonding the casing tothe formation.

Conventionally the cement is pumped down thecasing and displaced around the shoe into theannulus.

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Cementing

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Functions of Cements

Primary functions are : Provide support to the casings Zonal isolation-prevent fluid movement between

zones Casing protection against corrosive fluids Support wellbore Protect water zones

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Cement Job Planning

Each cement job must be carefully planned toensure correct additives are being used andsuitable placement technique is being employedfor that application.

The cement engineer must ensure that Cement can be placed correctly using the

available equipment Cement achieves adequate compressive strength Cement will isolate zones and support casing

throughout the life of well.

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Classification of Cement

Several classes have beenapproved by API

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Class A Intended to use from surface to 6000ft (1,830m) When no special properties are required. Similar to ASTM (American Society of Testing

materials) Type I Cheaper than other classes of cements

Class B Intended to use from surface to 6000ft (1,830m) Moderate to High sulphate resistance Similar to ASTM Type II Has lower C3A content than class A

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Class C Intended to use from surface to 6000ft (1,830m) When conditions require early strength Available in all 3 degrees of sulphate resistance

and similar to ASTM Type III.

Class D Intended to use from surface to 6000ft (1,830m)

to 10,000ft (3050m). Moderate and High sulphate resistance types

available Under moderately high temperatures and

pressures conditions.

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Class E Intended to use from 10,000ft (3050m) to

14,000ft (4720m) Under conditions of High temperature and

pressure. Available in MSR and HSR types

Class F Intended to use from surface to 10,000ft

(1,830m) to 16,000ft (4880m). Moderate and High sulphate resistance types

available Extremely 09High temperatures and pressures

conditions.

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Class G and H Intended to use from surface to 8,000ft (2440m) Can be used with accelerators and retarders to

cover a wide range of well depths andtemperatures

Class G Available in MSR and HSR Types, whileClass H is available in MSR Types only.

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Properties of Cement

Compressive strength To support the casing

string a compressivestrength of 500 psi isgenerally adequate

WOC ( Waiting onCement)-The timerequired for the cement toattain strength and settlebehind the casing.

The casing shoe should notbe drilled out untilstrength is attained.

Compressive strengthdepends upon

TemperaturePressureAmount of water mixElapsed time

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Properties of Cement

Thickening Time (Pump ability) Time required for cement slurry to be pumped

and displaced in the annulus. Slurry should have enough thickening time to

allow mixing ,pumping and displacement beforehardening.

Generally 2-3 hours thickening time whichincludes safety factor to allow for delays andinterruptions in operations.

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Properties of Cement Water Loss

If water is lost before cement reaches its intendedposition???

Amount of water loss depends upon the type of cementjob

Squeeze cement jobs require low water loss since thecement must be squeezed before filter cake builds upPrimary cementing is not so critical

Corrosion resistance Formation water may contain Na and Mg sulphates which

react with lime to form calcium sulphoaluminate. These crystals expand and cause cement to crack. Lowering C3A content increases sulphate resistance types

Slurry Density Vary between 11 to 18.5 ppg ,depending upon the type of

formation Density is varied for a low to high strength formation.

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Cementing Additives

Most slurries containadditives to modify theproperties of the slurry toproduce a better cementjob. Cement additives can be

used to Vary slurry density Change compressive

strength Accelerate and retard

setting time Control filtration and

fluid loss Slurry viscosity Additives may be granular

or liquid form, added withthe cement or mixed withwater.

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Cementing Additives Accelerators

Chemicals that reduce thickening time of slurry andincrease early strength

Used in conductors and surface casings to reduce WOC Common types of accelerators are :

Calcium chloride (CaCl2 )1.5-2%Sodium Chloride (NaCl) 2-2.5%Sea water

Retarders extends thickening time of cement slurry to aid proper

placement before hardening. Used in HT wells with Intermediate and production casings

and squeeze cement jobs Avoids cement setting prematurely Common types are:

Calcium lignosulphonate 1-1.5%Saturated Salt solutionsCellulose derivativesHydroxycarboxylic acids

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Cementing Additives Weighting Agents( Heavy

additives) Increases slurry density. Used when cementing over

pressurized zones Types are:

BariteHematite

Extenders (Light weight) Materials that lower slurry

density and increase yieldto allow weak formations tobe cemented withoutfracturing.

Allows more mix water tobe added

Types are:BentonitePozzolanDiatomaceous earthgilsonite

Source: Drilling DataHandbook, Editions Technip

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Cementing Additives Mud Contaminants

To Improve slurry properties additives such as Diesel Oil,thinners etc are added.

Prevents undesirable side effects caused by mud on cementsetc.

Dispersants (Friction Reducing Additives) Negatively charged polymer molecules that attach themselves

to positively charges in cement grains. Improves flow properties of slurry Lowers the viscosity so that turbulence will occur at lower

circulating pressure. Types are

Polymers 0.3-0.5 lb / sx of cementSaltCalcium lignosulphonate 0.5-1.5 lb / sx

Fluid Loss Additives Excessive fluid loss can cause ineffective cement setting Prevents slurry dehydration ,premature setting or reduces fluid

loss to formations Types are:

Organic polymers 0.5 -1.5 %CMHEC (Carboxy Methyl Hydroxy Ethyl Cellulose) 0.3 -

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Cementing HardwareGuide Shoe

Used to guide the casingthrough the hole with itsrounded nose.

Avoiding jamming casingin washed out zones ordeviated wells

Float Shoe Prevents the back flow into

the casing once cement isdisplaced behind casing.

Built in check valve that isflapper or ball type.

Float shoe takes extra time torun casing in hole

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Cementing Hardware

Float Collars The purpose of these landing collars is to

serve as a seat for cement plugs. Run normally 2 or 3 joints above the shoe,

known as shoe track.

Centralizers Centring the casing string for the success

of cement job. Types

Rigid-Positive centralizers are designedfor a casing-casing annular spaceFlexible or spring bow type are used in

centring in uncased holes. There aretwo types: straight and spiralled

They help toKeep casing out of key seatsPrevent differential stickingImprove displacement efficiency

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Cementing Hardware Cement Plug Designed to separate the different fluids when

pumped through the casing. Plugs prevent contamination and wipe casing from

mud Prevent over displacement of cement Give surface indication that cement placement is

complete. Allow casing to be pressure tested. Bottom Plug

Bursts when slight over pressure is exerted.Besides seperating,it scrapes walls as it moves Top Plug

Provides seal and withstand high pressuresPumped on the tail end of slurry and comes to

rest on bottom plug Scratchers

Run on casing to remove mud cake and break upgelled mud.

Promotes a better bond between cement andformation

TypesRotating ScratchersReciprocating Scratchers

Source:weatherford

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Cementing Hardware

Cementing Heads Provides connection between

discharge line from cementunit and top of casing

Designed to hold cement plugs Releases bottom plug, mix and

pump down cement slurry Release top plug and displace

cement without makingconnection.

Cement plug need to installedcorrectly in the heads.

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Cementing Hardware

Cementing Baskets Equipment to minimise losses of

cement slurry in weak zones Used in shallow to medium depths Curb fluid passage considerably, but do

not prevent pressure transmission.

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Lowering Casing

The casing must be lowered as fast as possible as time spent isNPT. Casing string lowering speed is controlled according to surge

pressures on wall and bottom. Carefully organized to prevent casing from being stuck. Spider and casing elevators are often used. Lengths of casing are screwed b means of hydraulic tongs. Driller monitors as casing string is filled up. Mud can be reconditioned and circulated while string is

manoeuvred and scratchers put to work. Circulation is stopped when

mud returns contains no more cuttings Low gas content No kicks or lost returns Homogeneous volume of circulating mud

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Cementing Operation Primary Cementing

Cement plugs placed correctly in cement head. Pump spacer ahead of cement. First plug (wiper) pumped down ahead of cement

to clean inside of casing. Landing collar acts as shoulder for bottom plug. Pressure surge ruptures bottom plug and allows

slurry to pass through and circulate into annulus. Slurry displaces mud and washes the outside wall

of casing as it flows. When slurry pumped down, top plug is released

and is pushed along down by drilling mud(flushing)

Pressure increases and top plug bumps againstlanding collar (not to exceed burst pressure)

Displace with spacer and low density mud.

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Cementing Operation

Source:drilling,NGUYEN

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Cementing Operation Stage Cementing Carried out usually in longer strings in which the

annulus need to filled completely. Requirements of high pump pressures, longer

pumping times and excessive hydrostatic pressurefrom cement column leads to cementing

First stage Similar to earlier procedure, except that a

smaller volume is used to cement lower part ofannulus depending upon fracture gradient.

Second Stage Involves a stage collar, which is made up into

casing string at pre determined depth. Stage collar are initially closed by inner sleeve,

held by retaining pins. After first stage is complete, a special dart is

released from surface opening ports allowingcommunication between casing and annulus.

Circulate through stage collar and pump spacer Pump secondary stage slurry and release closing

plug. Displace cement with mud. Top plug closes by moving a second sleeve

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Cementing Operation

Risk of channellingand poor cementbond may arise???

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Cementing Operation Inner String Cementing

Large diameter casing result in ??????Large displacement volumesLong pumping times

Cement casing through tubing or drill pipeCasing run as beforeSpecial float shoe-allows drill pipe to be

stabbedCement job can then proceed as before.Inner string can be retrievedSuitable for casings of 13 3/8 and

largerDisadvantage of NTP for running and

retrieving inner string.

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Cementing OperationLiner cementing

Has a full length float collar , landing collar andshoe installed.

Landing collar catches the cement wiper plug. Wiper plug is held on end of the tail pipe by

means of shear pins. Liner is run on drill pipe and hanger set at

correct point inside previous casing string. Mud is circulated out to ensure it is free of

debris. Before cementing, setting tool is backed off. Pump spacer ahead and followed by slurry. Release pump down plug and displace cement

out of liner. Pump down plug releases wiper plug. Both move down until Landing collar. Bump plugs with 1000 psi pressure. Bleed off and check for back flow. Excess cement used to seal top of liner. Once cement is set, setting tool is picked up

out of liner With tail pipe above liner, excess cement is

reversed circulated

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Cementing Operation

LinerCementing

Source:drilling,NGUYEN

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Cementing OperationProblems with cementing Liners

Minimal annular spacesClearance between 7 OD liner

and 8-1/2 hole.Difficult to run linerLost circulation problemsDifficult to centraliseCement placement poor

(channelling)

Mud contamination

Lack of pipe movement-due torisk of setting tool sticking

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Cementing Job

Recommendations Use centralisers at critical

points along the casing string Moving the casing-rotation

rather than reciprocation Before cementing, ensure mud

has good flow properties Displace cement under

turbulent conditions if possible Spacers to prevent mud

contamination in annulus.

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Secondary Cementing Operation

Squeeze Cementing

Process by which hydraulic pressure forcescement slurry through holes in casing intoannulus and formation

Often used as a remedial operation in workovers

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Applications To seal off gas and water producing zones and

maximize oil production from completioninterval.

Repair casing failure through leaking joints andcorrosion.

Seal off lost circulation zones. Remedial work on a poor primary cement job. Abandonment.

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Processes of squeezingcement

High Pressure Low Pressure

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Secondary Cementing OperationHigh Pressure Squeeze

Breaking down the formation andallowing cement slurry intofractured zone.

Carried out by solids free fluids water or brine.

Fracture occurs along planeperpendicular to direction of leastcompressive stress. At depths>3000 ft, vertical stresses aregreater than horizontal stresses.

After breaking formation, slurry ofcement is spotted adjacent toformation and pumped slowly.

Injection pressure gradually buildsup.

Pressure released for back flow. High Pressure squeeze jobs are

recommended for very dense andimpermeable formations.

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Low Pressure Squeeze

Efficient method to seal unwanted zones Slurry of finely divided solids in liquid is forced

into formation without fracturing. Liquid is forced into formation and solids build up

cake. Reverse circulate out excess cement. Often used for repairing primary cement job.

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Placement Techniques Braden head Squeeze Retrievable squeeze packer Drillable cement retainer

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Secondary Cementing OperationBraden head Squeeze

Pumping cement through drill pipewithout the use of packer.

Cement stopped at required depthand pressure build up is obtainedby closing BOPS at surface.

Displacing fluid is then pumpeddown, forcing cement intoperforations

Generally used for low pressurecement squeeze job.

DisadvantagesIt is difficult to place cement

accurately.Cannot be used for squeezing

off one set of perforations ifother are still open.

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Secondary Cementing OperationRetrievable Packer

Can be set and released as many timeson one trip.

Isolate casing and well head while highpressure is being applied.

Can be either compression set or tensionset.

By pass ports allow annularcommunication

Generally set 30-50ft above perforations. Sometimes tail pipe is used below packer

to ensure only cement is squeezed

Procedure for squeezingRun packer on drill pipe and set at

depth to with bypass openPump cement slurry ,displace cement

and allow fluid to flow through bypass portsClose port when cement slurry

reaches packer.Apply squeeze pressureRelease pressure and check back flowRelease packer, pick up and reverse

circulate.

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Drillable Retainer Contains two way valves to

prevent flow in either or bothdirections.

Used for primary cement jobsas well as closing waterproducing zones.

Run on drill pipe or wireline,once cement has beensqueezed, the drill pipe canbe removed, closing backpressure valve.

Can be used once then drilledout.

In multiple zones, retainerisolates lower perforations

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Cement PlugsCement Plugs

Designed to fill a length of casing or open holeto prevent vertical fluid movement

Used for:Abandoning depleted zonesSeal lost circulation zonesProviding KOP for directional wellsIsolating zone for formation testingSeries of plugs for well abandonment

PrecautionsSelection of clean hole to prevent contaminationCondition mud prior to placing plugPre-flush fluid ahead of cementDensified slurry to be used.

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Cement Plugs

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Cement Plugs

Balanced Plug Method achieves an

equal level of cement inthe drill pipe andannulus.

Preflush, cement slurryand spacer fluid arepumped down the drillpipe and displaced withmud.

Displacement continuesuntil level of cementinside and outside issame.

Drill pipe retrievedleaving plug in place.

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Cement PlugsDump Bailer Method

Set permanent bridge plug belowplug back depth

Cement bailer containing slurry isthen lowered down the well

When bailer reaches bridge plugthe slurry is released and set ontop

AdvantagesBetter depth controlReduced risk of contamination

DisadvantagesOnly small volume of cement

can be dumped and thereforeseveral runs requiredNot suitable for deep wells

unless retarders used.

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Cement Evaluation Tools

Cement job can be considered a failure if: Cement does not fill annulus to required height. Cement does not provide good seal at shoe. Cement does not isolate undesirable zones.

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Cement Evaluation Tools

Temperature surveys Running a recording

thermometer in thecasing aftercementing.

Thermometer respondsto heat generated bycement hydration todetect top of cement.

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Cement Evaluation Tools Cement Bond Logs

Indicate presence ofcement and bond.

Tool emits sonic signalsand receives at receiver.

Amplitude indicateswhether bond is strongor weak.

Channelling can also bedetected.

Radioactive surveys Radioactive tracers can

be added to cementslurry before it ispumped.

Carnolite is commonlyused and detects the topof cement in annulus.

Sonatrach Cementing

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