1. PETE 203 DRILLING ENGINEERING
CASING DESIGN

2. Objectives Understand primary functions of casing
Recognize the various types of casing strings used.
Understand the procedures used in the design of casing strings.

3. Types of Strings of Casing
1. Drive pipe or structural pile {Gulf Coast and offshore only} 150’-300’ below mud-line.
2. Conductor string. 100’ - 1,600’ (BML)
3. Surface pipe. 2,000’ - 4,000’
(BML)
Diameter Example
16”-60” ”
16”-48” ”
8 5/8”-20” /8”

4. Types of Strings of Casing
Diameter Example
4. Intermediate String
5. Production String (Csg.)
6. Liner(s)
7. Tubing String(s)
7 5/8”-13 3/8” /8”
4 1/2”-9 5/8” ”

5. Example Hole and String Sizes (in)
Hole Size
Pipe Size
36”
26”
17 1/2
12 1/4
8 3/4
Structural casing
Conductor string
Surface pipe
IntermediateString
Production Liner
30”
20”
13 3/8
9 5/8 7

6. Example Hole and String Sizes (in)
Hole Size
Pipe Size
36”
26”
17 1/2
12 1/4
8 3/4
Structural casing
Conductor string
Surface pipe
IntermediateString
Production Liner
30”
20”
13 3/8
9 5/8 7

7. Example Hole and String Sizes (in)
Structural casing
Conductor string
Surface pipe
Intermediate String
Production Liner
Mudline
250’
1,000’
4,000’

8. Example Casing Programs

10. CONDUCTOR (1 or 2) (40’ – 300’) SURFACE (300' - 5000')
Prevent eroding surface sediments and rig foundation by circulating the drilling fluid to the shale shaker.
Protects subsequent casing strings from corrosion.
Install director system on it.
SURFACE (300' ')
Control caving and washing out of poorly consolidated surface beds.
Protect fresh water sands from possible contamination by drilling fluid mud, oil or gas and or salt water from lower zone.
Install BOP on it.

11. INTERMEDIATE CSG (1 or 2) Contaminate drilling fluid.
It depends on well depth and geology in specific area.
Primary Purpose: To seal off troublesome zones which:
Contaminate drilling fluid.
Jeopardize drilling progress with possible pipe sticking, excessive hole enlargement.
Contain abnormal pressure fluids, protect formation below the surface casing from higher pressure credited by mud.

12. PRODUCTION CSG DRILLING LINER PRODUCTION LINER 2. Segregate pay zone.
1. It is set through productive interval to;
2. Segregate pay zone.
3. Can be used to produce fluid instead of tubing.
DRILLING LINER
1. Lower in cost.
2. Functions like intermediate.
PRODUCTION LINER
1. Lower in cost
2. Functions like production.

13. 6.2 Standardization of Casing
API: American Petroleum Institute Standards.
Range of length
Outside diameter
Wt/ft.
Type of coupling
Steel grade

14. Classification of CSG. 1. Outside diameter of pipe (e.g. 9 5/8”)
2. Wall thickness (e.g. 1/2”)
3. Grade of material (e.g. N-80)
4. Type to threads and couplings (e.g. API LCSG)
5. Length of each joint (RANGE) (e.g. Range 3)
6. Nominal weight (Avg. wt/ft incl. Wt. Coupling) (e.g. 47lb/ft)

15. Length of Casing Joints
RANGE ft
RANGE ft
RANGE > 34 ft.

16. OUTSIDE DIAMETER (4.5 -20") Minimum mandrel diameter that must pass
Tolerance %
Usually slightly oversized.
Minimum permissible
Wall thickness = 87.5% of nominal wall thickness.
Nominal = approximate average
Drift diameter : Check ID
Minimum mandrel diameter that must pass
Unobstructed through the pipe.
Insures a bit size less than drift diameter.

17. WEIGHT PER FOOT
Nominal wt/ft : is not true wt/ft but is useful for identification purposes as an approximate average (wt/ft)
Plain-end wt/ft: is the wt/ft of the pipe body excluding the threaded portion and coupling wt.
Average wt/ft: total wt. of avg. joint of threaded pipe with a coupling attached power tight of one of avg. joint.
For design calculation nominal wt/ft. is often used.

18. 6.3 Type of Coupling
A coupling is a casing connector which is made of casing material.
Most common types of casing. Joints are externally threaded from each end.
API specification the coupling should be of the same grade as the pipe body.

19. Casing Threads and Couplings
API round threads - short { CSG }
API round thread - long { LCSG }
Buttress { BCSG }
Extreme line { XCSG }
Other …

20. CSG & LCSG Tensile strength of the pipe body
These connectors have the same basic design:
Threads are round shaped and are spaced to give eight threads/inch.
Sometimes they are called API 8-round threads.
Threads are cut with a taper of 3/4 in/ft.
These are commonly used connectors because of their proven reliability, ease of manufacture and low cost.
Cut with a 60 angle, and has round peaks and roots.
Thread compound must be used to fill the voids and obtain a seal.
Tensile strength of the joint
Joint Efficiency = < 100%
Tensile strength of the pipe body

21. API BCSG CONNECTOR Joint efficiency is 100% in most cases.
It is tapered but longer thread run out ¾ inch/ft. for upto 75/8 inch.
Thread shape is square to reduce unzipping tendency.
5 threads cut to the inch.
1 inch/ft for 16 inch csg.

22. API XCSG CONNECTOR It is integral joint. Pipe thicker near the wall.
OD is less than other API couplings
Sealing mechanism is metal to metal seal between the metal and the box.
Much more expensive.

23. API Connectors

24. STRENGTH Strength is designated by casing GRADE
Grade code : Letter and number H-40, J-55, C-75, L-80
Letter is arbitrary.
Number designates the minimum yield strength of steel in thousands of psi.
Yield strength :tensile stress required to produce a total elongation per unit length of on a standard test specimen.
Minimum yield strength = 80% of average yield strength observed.

25. s e

26. Grades of Casing Recognized by the API

27. API Connectors

28. Tensile force balance on pipe body
Example 7.1:
Compute the body-yield strength for 20-in., K-55 casing with a nominal wall thickness of in. and a nominal weight per foot of 133 lbf/ft.

29. Tensile force balance on pipe body
K55
Solution:
This pipe has a minimum
yield strength of 55,000 psi
and an ID of:

30. Tensile force balance on pipe body
Thus, the cross-sectional area of steel is
and a minimum pipe-body yield
is predicted by Eq. 7.1 at
an axial force of:

31. Pipe Body Yield Strength
where

32. Pipe Body Yield Strength
Example
What is yield strength of body of 7”, 26 #/ft, P-110 casing?
(to the nearest 1,000 lbf).
…agrees with Tables

33. Internal Yield Pressure for Pipe (Burst)FT FP
where
FP = DLP
FT = 2tLYP
DLP = 2tLYP

34. Example For 7”, 26 #/ft P-110 pipe (to the nearest 10 psi)
…agrees with Tables.

36. TABLE 7.8 –COMMONLY USED BIT SIZES THAT WILL PASS THROUGH API CASING
(O.D., in)
Weight
Per Foot
(lbm/ft)
Internal
Diameter
(in.)
Drift
Commonly Used
Bit Sizes 4
9.5
10.5
11.6
13.5
4.09
4.052
4.000
3.920
3.965
3.927
3.875
3.795
3 7/8
3 ¾ 5
11.5
13.0
15.0
18.0
4.560
4.494
4.408
4.276
4.435
4.369
4.283
4.151
4 ¾

39. Casing Design - Collapse

40. Casing Design - Tension

41. Casing Design - Burst (from internal pressure)
Internal Yield Pressure for pipe
Internal Yield Pressure for couplings
Internal pressure leak resistance
Internal Pressure p p

42. Casing Design - Burst Example 1 Design a 7” Csg. String to 10,000 ft.
Pore pressure gradient = 0.5 psi/ft
Design factor, Ni=1.1
Design for burst only.

43. 1. Calculate probable reservoir pressure.
Burst Example
1. Calculate probable reservoir pressure.
2. Calculate required pipe internal yield
pressure rating

45. 23 lb/ft
26 lb/ft
N-80

46. Example
3. Select the appropriate csg. grade and wt. from the Casing tables:
Burst Pressure required = 5,500 psi
7”, J-55, 26 lb/ft has BURST Rating of 4,980 psi
7”, N-80, 23 lb/ft has BURST Rating of 6,340 psi
7”, N-80, 26 lb/ft has BURST Rating of 7,249 psi
Use N-80 CSG, 23 lb/ft

47. API Design Factors (typical)
Required
10,000 psi
100,000 lbf
Design
11,250 psi
180,000 lbf
11,000 psi
Collapse
Tension
Burst

48. Table 3 Grade D/t Ratio H40 16.44 and less J & K55 14.8 and less C75
P105
12.56 and less
P110
12.42 and less
(4)