Complete Casing Design with types of casing, casing properties, casing functions, design criteria and properties used for designing and one numerical problem

1. Lecturer
Syed Nawaz
Free Lance NDT Inspector
Founder of Petroleum Universe

2.  Introduction
 Functions of Casing
 Casing Types
 Approach to Casing Design
 Numerical Zone
 Conclusion
 References

3.  Hussain.et.al in Fundamentals of Sustainable Drilling says
that if a tubular is less 4.5 inch of diameter then it is tubing.
The range of casing diameter is 4.5” to 36”
 Once the section of subsurface is drilled, it has to be cased
with steel pipe, which is said to be Casing
 The reason behind the circular shape of casing is even
distribution of pressure
 Casing constitute 20-30% of the total cost of the well.

4.  Casing is installed to prevent the following
problems:
◦ Faults
◦ High pressure formations
◦ Toxic materials
◦ Thief zones, etc

5.  To protect near surface unconsolidated formations
 Provide protection against shallow gas flows
 Seal off shallow water zones
 Prevent caving of weak formations
 Provide protection against shallow blowouts
 It will ensure that formations at the casing shoe will not
fracture at the high hydrostatic pressure which may
encountered at later stage.
 Is usually set in the transition zone below or above an
over-pressured zone
 To seal off a severe loss zone
 To isolate producing zones,
 To provide reservoir fluid control
 To permit selective production in multizone production
 To isolate lost circulation or abnormally pressured zone

6.  It prevents cross channeling between two or more subsurface
fluid bearing layers
 To provide structural support for the wellhead and BOPs
 Note: Casing, Tubing, Drill Pipe must all confirm to API series
5 “Tubular Goods” including API Spec, ISO Specifications, etc

7.  Stove Casing
 Conductor Casing
 Surface Casing
 Intermediate Casing
 Production Casing
 Liner Casing

8.  These are marine conductor or foundation pile for offshore
drilling
 It is run to prevent washout of near surface unconsolidated
formations, to provide a circulation system
 This pipe does not carry any weight from the wellhead
equipment and can be driven into the ground or seabed
 The normal size for a stove pipe ranges from 26 in to 42 in

9.  Largest diameter
 Protect near surface unconsolidated formations, seal off
shallow water zones
 Size vary from 16 inch to 48 inch
 Conductor pipe is always cemented up-to the surface.

10.  Prevent caving of weak formations at shallow depths
 Shallow blowouts
 Depth of surface casing depends on aquifers and well head
pressure
 Diameter range is 18.625 to 20 inch in North Sea Operations
and casing size in middle east is usually 13.375

11.  Usually set in the transition zone below or above an over-
pressured zone
 Mainly design to overcome the problems like caving shale,
thief zones, mobile salt zones
 It ranges from 7.625 to 13.375 but no specific range of
length

12.  Last casing placed at the top of pay zone.
 Isolate producing zone
 Range is of 4.5, 5, 7 inches in O.D

13.  Do not reach the surface
 Mounted on liner hangers installed to previous casing string
(Intermediate Casing).
 In liner completions both the liner and the intermediate
casing act as the production string.
 The design criteria for liner is usually the ability to withstand
the maximum expected collapse pressure

16.  Design process
◦ Selection of Casing Sizes
◦ Selection of setting depths
◦ Definition of design properties
 Design properties
◦ Collapse pressure
◦ Burst pressure
◦ Yield strength: tensile and compressive
◦ Biaxial loading consideration
◦ Effect of Bending
 Design procedure
◦ Collapse pressure calculation
◦ Burst pressure calculation
◦ Tensile/ compressive strength calculation
 Safety factor

19.  Collapse
◦ Minimum external pressure required for pipe collapse (no
internal pressure or loads)

20.  Based on diameters and thickness there are 4
different types of collapse pressure
 The API bulletin 5C3 3 reports four formulas for
calculating the collapse resistance of tubular goods
and they are as follows:
◦ Elastic Collapse Pressure
◦ Transition Collapse Pressure
◦ Plastic Collapse Pressure
◦ Yield Strength Collapse Pressure

21. ◦ Yield Strength (x<15.545)
◦ Plastic (15.545 < x < 26.025)
◦ Transition (26.025 < x < 39.9)
◦ Elastic (x > 39.912)

22.  Under field conditions, a given casing section
will be under the combined action of external
and internal pressure and axial load due to its
own weight

23.  Minimum internal pressure at
which pipe permanently deformed
(pipe is to no or less external
pressure or axial loads)
 API Burst is given as
 Lame equation is also used for
burst pressure
 Wall-thickness correction factor
0.875 for standard API tubulars
when a 12.5% wall-thickness
tolerance is specified.

25.  The ability of a metal to tolerate gradual progressive force
without any permanent damage or deformation.
 Classified into 2 pressures or loading: Axial Load and
Compressive Load
 Applying force on a structure directly along the structure axis

27.  API Design Factors Forces Range (Globally
used)
Collapse 1.0-1.125 (1.125)
Tension 1.0-2.0 (1.8)
Burst 1.0-1.33 (1.1)
Triaxial 1.25

28.  Casing Size
 Connections
 Weight
 Grade
 Length

29.  The OD is recognized as the size of Casing.
 The size of casing vary from 4.5” to 36”
 Drift Diameter: allowable diameter for next coming tool
 Breaking out the sequence then factors are to be estimated
such as
◦ Connections
◦ Mud weight
◦ Cementing
◦ Dogleg severity

31.  Pipe weight is usually expressed as weight per unit length in
lb/ft.
Weight Outer
dia
Inner
dia
Wall
thickness
Drift
dia
lb/ft in in in in
53.5=1658 9.625 8.535 0.545 8.379
47= 1457 9.625 8.681 0.472 8.525
43.5 =1348 9.625 8.755 0.435 8.599
40 = 1240 9.625 8.835 0.395 8.679
31

32.  The steel grade of the casing relates to the tensile strength of
the steel from which the casing is made
 Grade is a dependent property (Chemical Composition,
Mechanical Properties)
 The steel grade is expressed as a code which consists of a
letter and a number

33.  API Casing length ranges
 Most commonly used are R-2
Ranges Ranges of
Length (ft)
Average Length
(ft)
R-1 16-25 22
R-2 25-34 31
R-3 >34 42

35.  API provides 4 types of Casing connectors:
◦ CSG short round threads and couplings
◦ LCSG long round threads and couplings
◦ BCSG buttress threads and couplings
◦ XCSG extreme line threads
 CSG and LCSG combined are called API 8-
Round threads

36.  An intermediate section of 17.5 size was planned to be drilled at a
depth of 14,000 ft. A 13 3/8 OD casing is to be set and cemented in
this section. There are four casing types available in stocks which
are shown in Table below. Maximum burst pressure has to be
assumed when casing is full of 15.8 ppg cement slurry and fluid in
the annulus is water. In addition, maximum collapse pressure has to
be assumed when casing is full of fresh water and annulus is full of
15.8 ppg cement slurry. Safety factor for burst and collapse was
designed to be 1.18 and 1.15 respectively. Design a casing that
should be used in this section.

37. Depth of the casing shoe = 14,000 ft
Density of cement slurry 15.8 ppg
Density of fresh water = 8.34 ppg
Collapse safety factor = 1.15
Burst safety factor = 1.18

38.  Estimate the collapse and burst pressure for the available
casing sizes along with safety factor
 Then estimate collapse and burst pressure of required depth
without safety factor
 Based on magnitude select the casing

39.  Estimating Collapse pressure with the help of outer, inner
diameter and yield strength
 Estimating collapse pressure and burst pressure with
reference to depth

40.  For ID 12.031 inch

42. = 0.052 X 14000 X (15.8 – 8.34)
= 5430.88 psi
= 0.052 X 14000 X (15.8 – 8.34)
= 5430.88 psi

43.  The collapse pressure with safety factor is 5740 and burst
pressure is 5961 and the calculated magnitude is 5430.88
which lies between the above values. Thus 12.031 inch ID
casing is best.

44.  Hussain Rabia “Well Engineering and Construction”
 Hussain Rabia “Oil Well Drilling Engineering Principles and Practice”
 Hussain and Majid “Fundamental of Sustainable Drilling”
 “Formulas and Calculations for Drilling Operations” by G.James
 “Formulas and Calculations for Drilling, Production and Workover” by
Lapeyrouse
 Working Guide to Drilling Equipments and Operations by Williams Lyons
 Drilling Engineering Workbook by Baker Hughes
 “Drilling Engineering Technology” by Nediljka Gaurina Medimurec University
of Zagreb
 Advanced Oil Well Drilling Engineering by Mitchell
 Petroleum Well Construction Directional Drilling by Halliburton
 Adam.et.al “Applied Drilling Engineering”
 Drilling Engineering A complete well planning Aprroach by Neal Adam
 Petroleum Engineering Handbook by Warner Jr.
 Practical Field Reports I can’t mentioned their names

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