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Robert Gordon University and Owen S. Jenkins Ltd. 2010
ENM201 Wells
Casing and Tubing
Prepared and presented by
Owen Jenkins.
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Robert Gordon University and Owen S. Jenkins Ltd. 2010
Casing
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Robert Gordon University and Owen S. Jenkins Ltd. 2010
Casing
Pipe usually made of steel
A type of OCTG Oil Country TubularGoods
Other types include
Tubing Line pipe and
Drill pipe
Held together with threaded couplings
Both standard and premium proprietary types
are available
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Casing
Commonly used specifications:
API Spec 5CT/ISO 11960API Spec 5CT/ISO 11960 Specification forCasing and Tubing, Petroleum and natural gas
industries Steel pipes for use as casing or tubing
for wells (includes Errata dated April 2006) 8th
Edition, July 2005 Up to 20 OD
ISO 13680:2008ISO 13680:2008 Petroleum and Natural GasIndustries - Corrosion-Resistant Alloy SeamlessTubes for Use as Casing, Tubing and Coupling Stock
- Technical Delivery Conditions. 2nd. Edition.
Up to 339.73 mm OD (=13 3/8)
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Functions of Casing
Prevent caving of the wellbore
Prevent formation breakdown from high mudweight
Isolate zones of abnormal pressure
Seal off lost circulation zones (thief zones) To provide a means of completing and
producing the well efficiently
Provide structural support for wellheads andblow-out prevention equipment
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DifferentCasing
Strings
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Casing Programmes
Casing: considerable part of the overall well cost (
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Cementing Casing
Inner Casing String
Outer Casing String
Cement Sheath
Cement being injected
Casing is cemented
in place to:- Seal the casing in
the wellbore
Ensure a competent
pressure control
system Provide structural
support for the
casing
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Types of Casing
Conductor (or stove pipe)
Surface Casing
Intermediate Casing
Production Casing
Liner
Getting
smaller
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Conductor Casing or Pipe
Conductor: the first casing string to be run Often driven into the formation using large hydraulic jack-
hammers or pile-drivers.
Consequently has the largest diameter
Protects seabed formations from washouts through
erosion Protects surface formations which may have low
frictional strength
Could be exceeded by hydrostatic pressure exerted by drillingfluid when drilling a deeper section of the wellbore
Provides a conduit for mud returns
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Surface Casing
The main functions are:-
To seal off any fresh water sands Provide structural support for the blow-out
preventer (BOP) and wellhead equipment
Where abnormal pressures are expected the
setting depth is important
If the casing is set too high the formationstrength at the shoe may be too low to handle a
kick when drilling the next section
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Intermediate Casing
Intermediate, or protection casing
Used to isolate any troublesome formations whichwould/could cause drilling problems in the wellbore e.g.
sloughing shale
lost circulation high pressure zones
Several strings of intermediate casing may be required Depending upon the number of problems encountered
If rock formations are stable, drilling can be undertaken forrelatively long periods of time prior to the setting of casing
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Intermediate Casing
The setting depth depends on a
knowledge of pore pressures and fracture
gradients
During drilling operations the mud weight
controls pore pressures, but must not
exceed the fracture strength of shallower,un-cased zones
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Pore Pressure
The pressure of fluids within the pores of a reservoir
(usually hydrostatic pressure) or the pressure exertedby a column of water from the formation's depth to sea
level
When impermeable rocks (such as shales) form as
sediments are compacted, their pore fluids cannot
always escape and must then support the total
overlying rock column, leading to anomalously high
formation pressures
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Pore Pressure and Pressure
Gradient
Diagram courtesy of Schlumberger
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Production Casing
Usually the last string of CASING to be
run in the wellboreMay run through the pay zone
(reservoir)May be set just above the pay zone
For an open hole completionOr
Reservoir may have a LINER set across it.
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Production Casing:
Purpose
To isolate the production interval fromother formations such as water bearingsands
To protect the completion tubing Through which the reservoir fluids will be
transported to the surface
Production casing should be thoroughlypressure tested.
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Production Casing:
Testing
Usually pressure tested to around60% of its specified burst (internal
yield) pressure
If casing withstands that pressure it is
expected to be capable of
withstanding higher pressures
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Liner
A liner is a string of casing which does not extend backto the surface.
It is run back inside the previous casing string to providesome overlap
May be used either as an intermediate or production
string Much cheaper than a full length casing string
If required, a tie back string can be run to extend theliner back to the wellhead
A liner is usually less than 5,000 feet long.
Overlap typically 200500 feet
Liner overlap (liner lap) must be gas tight
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Casing vs. Bit Size (illustrative)
CasingSize ~20 ~133/8 ~95/8 ~7 ~ 5
Bit Size
(Typical)
24 to
26
16 to
17121/4
83/8 to
97/8~ 6
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Casing Setting Depth
The initial selection based on anticipated porepressures and fracture gradients
PP - Pressures at which fluid will come out of the formation FG - Pressures at which pumped fluid will fracture the
formation.
Consider relevant offset data in the estimatingpore pressures and fracture gradients
Also effect of hole angle on offset fracture
gradient
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Casing Setting Depth
The total depth of the well, and hence the
setting depth of the production casing orliner, is driven by logging, testing, and
completion requirements.
The shoe must be set deep enough to givean adequate sump for logging, perforating,
and to enable testing of the reservoir fluids
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Selecting Casing Setting Depth
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1) Draw the mean pore
pressure gradient curve
along with the lithology,if available
Selecting Casing Setting Depth
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2) Draw the mud weight
curve. The mud weight
curve should include a
200 to 400 psi trip
margin
Selecting Casing Setting Depth
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3) Draw the predicted
fracture gradient curve
Selecting Casing Setting Depth
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4) To determine initial
estimates of casing
setting depths
First:
Enter the mud weight
curve at Point A
(Total Depth (TD))
Selecting Casing Setting Depth
S l i C i S i D h
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4.2) Move up to Point Bwhich determines the
initial estimated setting
depth for the
intermediate casing
(actually run it 300400feet deeper)
Selecting Casing Setting Depth
S l ti C i S tti D th
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4.3) Move across to
Point C which
identifies the mud
weight requirement
for that depth
Selecting Casing Setting Depth
S l ti C i S tti D th
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4.4) Move up to Point D
which determines the
preferred setting depth
for the surface casing/intermediate string
Selecting Casing Setting Depth
S l ti C i S tti D th
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4.5) Move across to Point
E to identify the mud
weight required at thatdepth
Selecting Casing Setting Depth
S l ti C i S tti D th
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4.6) Point E is the normal pressure range and
no further casing is required to withstand the
associated mud weight. However, a
structural and conductor casing arerequired, and the setting depth criteria for
those strings are discussed later
Selecting Casing Setting Depth
Other Factors Affecting
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g
Casing Programme
Ifshallow gas zones are encountered whilst drilling,operations must stop and casing must be set
Iflost circulation zones are encountered: Drilling should stop
Mud returns should be checked
Lost Circulation Material (LCM) pumped downhole before themud is conditioned to a more suitable rheology
The zone will then need to be drilled before casing can be set
Formation stabili ty: if the formation is sensitive to themud weight over time, casing may have to be set
Other Factors
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Other Factors
Directional well profile:
Important to line out the well trajectorybefore setting casing
Attempt to achieve a consistent surveyahead of a tangent.
Long open hole sections may require
casing to reduce the risk of stuck pipe and
the level of torque
Other Factors
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Other Factors
Side-tracking requirements
As specified in the drilling programme.
For example: the 13-3/8 casing may be
set high enough to allow9-5/8 casing to be cut and pulled,
enabling a side-track in 12-1/4 hole
Other Factors
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Other Factors
Fresh water sands:
Need to protect drinking water, and not
contaminate it with drilling fluid.
Hole cleaning:
Particularly if a long section of 17-1/2 hole
is required.
Other Factors
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Other Factors
Salt sections
High pressure zones; Casing shoe should be set in competent
formations
Uncertainty in depth estimating
Require a margin related to confidence limit
when setting close to a permeable formation. Best source for this information is offset well
data or area experience, but this should be
documented
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Kick Tolerance
Once the initial casing setting depths are selected, the
kick tolerance associated with those depths should be
determined.
Start from TD up to the surface to determine the kick
tolerance and preferred setting depth for each casing
string.
The acceptability of kick tolerance values of less than
100 bbls should always be justified
By review of the type of well
Capacity of rig equipment for kick detection
Operator/Drillers experience, area experience and geology
Design Bottom-to-Top AND
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Top-to-Bottom
A design should be developed by well planning thatprovides for economic production from the pay zone
consistent with safety requirements. The pay zone should be analysed for its flow potential
and likely drilling problems.
The well should be designed initially from bottom-to-top. The opposite approach may result in a well that limits the
production capacity
Also necessary to work the other way around: it isessential to have a well design which is do-able withthe rigs and equipment available.
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Design of the Completion Tubing
Must be able to transport oil or gas to the surface at
economical rates.
Small diameter tubing tends to choke the flow rate due tohigh frictional pressures
Large diameter strings are usually preferable for good flow rate
BUT may be more prone to slugging depends upon GOR andnature of fluids
Small completion tubing can also lead to operational problems
due to reduced radial clearances
The completion design must be taken into account whendesigning the casing string
F th R di
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Further Reading
Bourgoyne, A.T., Jr., Chenevert, M.E., Millheim,
K.K., Young, F.S., Jr. 1986, Applied DrillingEngineering (Society of Petroleum Engineers)
Chapter 7 Casing Design
Devereux, S., 1998, Practical Well Planning andDrilling Manual (PennWell)
Chapter 1.4 Casing Design
Chapter 2.6 Casing Running Program
H l f l W b it
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Prepared byOWEN S. JENKINS LTD.4, Charlton Avenue, Aboyne, Aberdeenshire, AB34 5GL,
Scotland.
Tel. +44 (0)13398 87779. Mobile phone: +44 (0)7803 296779.
Email: [email protected]: www.osjl.co.uk
Acknowledgement: The foregoing slides were largely developed
from material supplied by colleagues at RGU.
ENM201 Wells
Casing and Tubing
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