Casing/Tubing design manual october 2005 Chevron
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Casing/Tubing Design Manual i
October 2005
Contents
1 Overview...........................................................................................................1-1
1.1 Introduction.................................................................................................1-1
1.2 Why Casing?..............................................................................................1-1
1.3 Casing Classifications ................................................................................1-3
1.4 Production Tubing ......................................................................................1-5
1.5 Tubular Combinations ................................................................................1-6
1.6 Anticipated Loads.......................................................................................1-6
1.7 Failure Modes.............................................................................................1-8
1.8 Organization of Text.................................................................................1-10
1.9 References...............................................................................................1-13
2 Tube Setting Depth and Size............................................................................2-1
2.1 Introduction.................................................................................................2-1
2.2 Casing Setting Depths................................................................................2-1
2.3 References...............................................................................................2-14
3 Tube Specification ............................................................................................3-1
3.1 Introduction.................................................................................................3-1
3.2 Standards...................................................................................................3-1
3.3 Groups........................................................................................................3-2
3.4 Manufacturing Process...............................................................................3-3
3.5 Chemistry ...................................................................................................3-4
3.6 Inspection and Testing ...............................................................................3-5
3.7 Couplings .................................................................................................3-14
3.8 Marking, Coating, and Thread Protection.................................................3-15
3.9 Sour Service.............................................................................................3-15
3.10 Temperature Effects ............................................................................3-16
3.11 References ..........................................................................................3-21
4 Tube Performance Properties...........................................................................4-1
4.1 Introduction.................................................................................................4-1
4.2 Collapse Strength.......................................................................................4-1
4.3 High Collapse Casing.................................................................................4-7
4.4 Collapse Due to Non-Uniform Loading.......................................................4-9
4.5 Operational Considerations......................................................................4-11
4.6 The Thick Wall Alternative........................................................................4-12
4.7 Effect of Wear on Collapse Resistance....................................................4-12
4.8 Burst Strength...........................................................................................4-13
4.9 Tube Body Yield.......................................................................................4-17
4.10 Tension/Compression Strength ...........................................................4-20
4.11 References ..........................................................................................4-20
5 Tube Connections.............................................................................................5-1
5.1 Introduction.................................................................................................5-1
5.2 Joint Strength .............................................................................................5-2
ii Casing/Tubing Design Manual
October 2005
5.3 Leak Resistance......................................................................................... 5-3
5.4 Internal Stresses ........................................................................................ 5-5
5.5 Other Considerations .................................................................................5-5
5.6 Chevron-Approved Connections ................................................................ 5-6
5.7 Tabulate Summary on Standardized Approved Premium Connections ...5-14
5.8 Connection Information............................................................................ 5-15
5.9 References...............................................................................................5-43
6 Tube Loads....................................................................................................... 6-1
6.1 Introduction ................................................................................................ 6-1
6.2 Tube Load Conditions................................................................................6-1
6.3 Environmental Changes............................................................................. 6-3
6.4 Tube Load Definitions ................................................................................ 6-5
6.5 Integrity with Cement..................................................................................6-7
6.6 Tube Basic Loads ......................................................................................6-7
6.7 Surface Casing......................................................................................... 6-13
6.8 References...............................................................................................6-15
7 Tube Buckling...................................................................................................7-1
7.1 Introduction ................................................................................................ 7-1
7.2 Effective Tension........................................................................................7-2
7.3 Buckling in a Vertical Wellbore...................................................................7-3
7.4 The Neutral Point .......................................................................................7-4
7.5 Buckling in an Inclined Wellbore ................................................................7-5
7.6 Buckling in a Curved Wellbore ................................................................... 7-6
7.7 Effect of Inclination Increase (Build)...........................................................7-8
7.8 Effect of Inclination Decrease (Drop)..........................................................7-9
7.9 Effect of Azimuth Change (Turn)................................................................7-9
7.10 Length Change in a Vertical Wellbore...................................................7-9
7.11 Length Change in Inclined and Curved Wellbores............................... 7-11
7.12 Permanent Corkscrewing.................................................................... 7-11
7.13 References..........................................................................................7-13
8 Tube Design.................................................................................................... 8-1
8.1 Introduction ................................................................................................ 8-1
8.2 Design Factors...........................................................................................8-1
8.3 HPHT Wells................................................................................................8-3
8.4 Casing Design Criteria ...............................................................................8-5
8.5 References...............................................................................................8-10
9 Example Designs.............................................................................................. 9-1
9.1 Introduction ................................................................................................ 9-2
9.2 Stretch in a Vertical Wellbore, Single String............................................... 9-3
9.3 Stretch in a Vertical Wellbore, Tapered String ........................................... 9-7
9.4 Tubing Movement ......................................................................................9-8
9.5 Production Casing Design........................................................................ 9-18
10 Steam Injection Casing Design.......................................................................10-1
10.1 Introduction..........................................................................................10-1
10.2 Casing Thermal Load in Steam Injection Wells................................... 10-1
10.3 Other Issues......................................................................................10-15
Casing/Tubing Design Manual iii
October 2005
10.4 References ........................................................................................10-15
11 Casing Design for Deep Water Wells..............................................................11-1
11.1 Introduction..........................................................................................11-1
11.2 Sustained Casing Pressure .................................................................11-1
11.3 Alternatives for Mitigation of TAPB......................................................11-2
11.4 WELLCAT
™
Modeling of Pressure Build Up........................................11-7
11.5 References ..........................................................................................11-9
12 Probabilistic Casing Design Concept..............................................................12-1
12.1 Introduction..........................................................................................12-1
12.2 Probabilistic Casing Design Approaches.............................................12-3
12.3 Load and Resistance Factor Design (LRFD).....................................12-10
12.4 Probabilistic Casing Design Applications...........................................12-10
12.5 References ........................................................................................12-11
13 Tubing Design.................................................................................................13-1
13.1 Introduction..........................................................................................13-2
13.2 Tubing Features...................................................................................13-2
13.3 Anchoring Systems..............................................................................13-5
13.4 Tubing Connections.............................................................................13-6
13.5 Tubing Stress Analysis ......................................................................13-10
13.6 Collapse Design.................................................................................13-12
13.7 Tubing Load Cases............................................................................13-12
13.8 Pressure Testing................................................................................13-13
13.9 Acid Stimulation.................................................................................13-13
13.10 Fracturing...........................................................................................13-13
13.11 Flowing ..............................................................................................13-14
13.12 Shut-In...............................................................................................13-14
13.13 Tubing Movement..............................................................................13-14
13.14 Evaluation of Total Length Change....................................................13-23
13.15 Tubing to Packer and Packer to Casing Force ..................................13-23
13.16 Materials and Corrosion.....................................................................13-29
13.17 Corrosion Caused By CO
2
and Cl......................................................13-37
13.18 Ordering Specifications......................................................................13-44
A Casing Design Spreadsheet.............................................................................A-1
B Casing Design Software ...................................................................................B-1
B.1 Introduction.................................................................................................B-2
B.2 StressCheck
™
.............................................................................................B-2
B.3 Matching StressCheck™ Load Cases to Recommended Design Load Cases for
Standard Wells .....................................................................................................B-9
B.4 Matching StressCheck™ Load Cases to the Recommended Design Load Cases
for HPHT Wells...................................................................................................B-11
B.5 CWEAR....................................................................................................B-14
B.6 Wear and Casing Design Software...........................................................B-16
C Tubing and Critical Well Casing Design Software............................................ C-1
C.1 Introduction........................................................................................... C-1
C.2 WELLCAT
™
.......................................................................................... C-1
D Basic Equations............................................................................................... D-1
D.1 Introduction........................................................................................... D-2
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October 2005
D.2 Strain-Displacement Relations ..............................................................D-2
D.3 Stress and Equilibrium...........................................................................D-9
D.4 Stress-Strain Relations........................................................................D-13
D.5 Multi-Dimensional Loading..................................................................D-21
D.6 Loading and Deformation of a Thick Cylinder......................................D-35
D.7 Approximations for a Thin Cylinder......................................................D-41
D.8 Changing Environmental Conditions ...................................................D-45
D.9 References..........................................................................................D-51
N Nomenclature...................................................................................................N-1
G Glossary.......................................................................................................... G-1
1
1 Overview
1.1 Introduction ......................................................................................................................1-1
1.2 Why Casing?....................................................................................................................1-1
1.2.1 Rock is Permeable ......................................................................................................1-2
1.2.2 Rock is Weak ..............................................................................................................1-2
1.2.3 Rock is Chemically Active ...........................................................................................1-2
1.3 Casing Classifications......................................................................................................1-3
1.3.1 Surface Casing............................................................................................................1-3
1.3.2 Intermediate or Protective Casing ...............................................................................1-4
1.3.3 Production Casing.......................................................................................................1-4
1.3.4 Liner/Tieback...............................................................................................................1-4
1.4 Production Tubing............................................................................................................1-5
1.5 Tubular Combinations......................................................................................................1-6
1.6 Anticipated Loads.............................................................................................................1-6
1.7 Failure Modes ..................................................................................................................1-8
1.8 Organization of Text.......................................................................................................1-10
1.9 References.....................................................................................................................1-13
1.1 Introduction
This text details the engineering mechanics fundamentals upon which modern oil
well tubular design is based. Restricting the scope of the discussion to the area
of basic concepts omits a great deal of quality material that has appeared in the
literature concerning the practical aspects of specific tubular designs.
Conversely, review of particular applications without sufficient background in
design fundamentals can result in incorrect and misleading conclusions. The
intent here is to present information of a general nature that should be mastered
prior to the consideration of the idiosyncrasies of a specific locale. More
practically oriented essays can then be perused at the reader’s initiative and
according to the particular geographic location or field circumstances of interest.
1.2 Why Casing?
If all subsurface rock formations were composed of competent, leak-proof
material casing the wellbore would be unnecessary. Casing is necessary,
however, and it is inserted in a wellbore because of certain inadequacies of rock.
Casing/Tubing Design Manual 1-1
October 2005
1.2.1 Rock is Permeable
The fact that rock accommodates interstitial fluid flow and, therefore, the
exchange of fluids between the wellbore and surrounding formations has several
consequences:
• Fluid loss or gain at the wellbore wall suggests mixing between high- and
low-pressure formations and between hydrocarbon- and non-hydrocarbon-
bearing rock, both of which can be undesirable.
• The influx of relatively high pressure fluids into the wellbore, termed a “kick,”
can lead to well control events that endanger surface personnel and
equipment.
• Rock permeability promotes the formation of a mud cake at the wall of the
wellbore leading to the phenomenon of differential sticking.
1.2.2 Rock is Weak
Despite the damage that can be dealt metal structures, including wellbore
tubulars by formation movement, compared to steel, rock is weak. This is
particularly true in load conditions that place rock in tension. Insufficient wellbore
pressure can result in spalling, sloughing, and caving of the wellbore. Excess
wellbore pressure can result in fracture of the wellbore wall, loss of potentially
expensive drilling fluid, and, possibly, a well control event.
1.2.3 Rock is Chemically Active
Chemical stability addresses the transport of water from the wellbore into the
formation and subsequent rock-fluid interaction. Water is generally accepted to
move into the formation by several mechanisms. The result may be observed as
an increase in pore pressure and a decrease in the cohesive strength of the rock
because of a softening of the rock matrix [Chenevert, 1970; Bailey, 1991;
Colback and Wiid, 1965]. Either or both effects can cause a decrease in the
stability of the wellbore. Chemical mechanisms must be coupled with the
mechanical response to completely determine wellbore stability [Mody and Hale,
1993].
The degree of strength decrease accompanying fluid invasion will depend on the
type of formation. Sandstones and carbonates, for example, with cementation
provided by authigenic overgrowth formed from minerals in solution after original
deposition, will show a minimum effect from water. Shales or other materials
where cementation is provided largely by a clay matrix exhibit a large effect.
The variety and relative water sensitivity of clays comprising the class of rocks
denoted “shale” are beyond the scope of this discussion. Suffice it to say that
isolating such formations with casing, which is for all practical purposes is inert to
water, eliminates wellbore stability concerns related to chemical stability as
shown in Figure 1-1.
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October 2005
Casing
Formation
Wellbore fluid
Figure 1-1. Casing, Formation, and Wellbore Fluid
1.3 Casing Classifications
As used here, the term “casing” includes those tubulars installed in a wellbore for
the purpose of stabilizing the hole and isolating and controlling subsurface
pressures and fluids
1
. Depending on the depth interval in which casing is run,
additional, more specific, functions may also apply.
It is common in the petroleum industry to distinguish the types of casing
according to their intended application. In this sense, a particular casing size may
be classified differently according to its use in a well.
The four most common classifications of casing are as follows:
1.3.1 Surface Casing
The shallowest string of casing run is termed “surface casing.” Surface casing
has two primary functions: (1) support of wellhead equipment and, therefore,
subsequent casing strings hung from the wellhead
2
and (2) isolation of shallow
1
A constant companion of the casing string is the sheath of cement placed in the
casing/wellbore annulus. The importance of the cement sheath in completing the
segregation of downhole fluids and pressures cannot be overemphasized. Although even
a cursory treatment of cement design and placement is beyond the scope of this
discussion, suffice it to say that the best casing design imaginable is of no use if coupled
with a poorly placed cement column.
2
In some applications, this function may be assigned to an even shallower conductor
string that is usually either pile driven or jetted into surface formations. The conductor
string is also used to (a) provide a conduit for drilling fluid, (b) isolate shallow
formations that may wash out or cave into the wellbore, and (c) bypass low stress zones
near the surface that might fracture, leading to lost circulation. Conductor casing is not
listed in the main body of the text, as the depths to which it is run are usually not
sufficient to warrant a formal design.
Casing/Tubing Design Manual 1-3
October 2005
fresh water aquifers to avoid contamination by wellbore fluids. The depth to
which surface casing will be run depends on the depth of the target location
and/or the depth of shallower zones that must be isolated. However, normally the
surface casing string does not exceed 300 m (1,000 ft.) in length.
1.3.2 Intermediate or Protective Casing
Subsequent strings of casing run between the surface string and the innermost
production string are termed “intermediate” or “protective” casing. One specific
application of intermediate casing is to allow the adjustment of drilling fluid weight
to account for anomalies in subsurface pore pressure. For example, it may be
that down to a certain depth, drilling can proceed with the formation pore
pressure being contained by a drilling fluid having a density of 1,200 kg/m
3
(10
lb/gal). However, for some interval below that depth, abnormalities in the
subsurface formation pressure may require an increase in fluid density.
Remaining at the lower fluid weight of 1,200 kg/m
3
(10 lb/gal) would induce the
flow of formation gas into the wellbore with the resultant possibility of a gas kick
and a blowout. On the other hand, drilling with the heavier fluid weight down to
and including the abnormally high-pressured zone would result in continuous
circulation problems due either to loss of drilling fluid, to shallower zones having
a lower hydrostatic pressure in the pore structure, or to fracturing a shallower
formation by exceeding its closure stress. The solution to such a circumstance is
to interrupt drilling at the top of the abnormally pressured zone and run a string of
intermediate casing. The fluid weight for future drilling can then be increased to
contain the abnormal pressure zone, while avoiding injurious contact of this
heavier fluid with shallower formations.
Additional functions of intermediate casing include the segregation of formation
fluids and intermediate stabilization of the wellbore before reaching the target
depth of the well. Finally, should a subsurface kick occur, a previously set
intermediate casing string provides a safe chamber to control the pressures
associated with the kick.
1.3.3 Production Casing
The last tubular string run in a wellbore, after the target depth has been reached,
is referred to as the “production casing string.” According to the type of
completion, the production casing string may actually serve as a conduit for
reservoir fluids (annular flow between the production casing and tubing).
Normally, however, reservoir fluids are produced through tubing with the annulus
between the tubing and production casing being sealed by a packer. In this
manner, the tubing/production casing annulus can serve a variety of purposes,
such as a conduit for the injection of corrosion inhibitors or for the installation of
artificial lift equipment and subsurface safety valves.
1.3.4 Liner/Tieback
One final classification of casing that increases in importance as the well depth
increases is the liner/tieback string. As the well depth increases, the possibility of
1-4 Casing/Tubing Design Manual
October 2005