1. PETE 411 Well Drilling
Lesson 17 Casing Design

2. Casing Design Why Run Casing? Types of Casing Strings
Classification of Casing
Wellheads
Burst, Collapse and Tension
Example
Effect of Axial Tension on Collapse Strength

3. Read Applied Drilling Engineering, Ch.7
HW # Due

4. Casing Design What is casing? Casing Cement Why run casing?
1. To prevent the hole from caving in
2. Onshore - to prevent contamination of fresh water sands
3. To prevent water migration to producing formation

5. Casing Design - Why run casing, cont’d
4. To confine production to the wellbore
5. To control pressures during drilling
6. To provide an acceptable environment for subsurface equipment in producing wells
7. To enhance the probability of drilling to total depth (TD)
e.g., you need 14 ppg to control a lower zone, but an upper zone will fracture at 12 lb/gal.
What do you do?

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

7. 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” ”

8. 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

9. 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

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

11. 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. 47 lb/ft)

12. s e

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

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

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

16. Abnormal
Normal Pore Pressure Abnormal Pore Pressure psi/ft gp > normal

17. Design from bottom

18. X-mas Tree Wellhead Hang Csg. Strings Provide Seals
Press. Gauge
X-mas Tree
Wing Valve
Choke Box
Master
Valves
Wellhead
Hang Csg. Strings
Provide Seals
Control Production from Well

19. Wellhead

20. Wellhead

21. Casing Design Tension Tension Depth Burst Collapse Collapse STRESS
Burst: Assume full reservoir pressure all along the wellbore.
Collapse: Hydrostatic pressure increases with depth
Tension: Tensile stress due to weight of string is highest at top
Burst

22. Casing Design Collapse (from external pressure)
Yield Strength Collapse
Plastic Collapse
Transition Collapse
Elastic Collapse
Collapse pressure is affected by axial stress

23. Casing Design - Collapse

24. Casing Design - Tension

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

26. 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.

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

28. Example
3. Select the appropriate csg. grade and wt. from the Halliburton Cementing 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

30. 23 lb/ft
26 lb/ft
N-80

31. Collapse Pressure The following factors are important:
The collapse pressure resistance of a pipe depends on the axial stress
There are different types of collapse failure

32. Collapse Pressure
There are four different types of collapse pressure, each with its own equation for calculating the collapse resistance:
Yield strength collapse
Plastic collapse
Transition collapse
Elastic collapse

33. Collapse pressure - with axial stress 1.
Casing Design
Collapse pressure - with axial stress 1.
YPA = yield strength of axial stress equivalent grade, psi
YP = minimum yield strength of pipe, psi
SA = Axial stress, psi (tension is positive)

34. Casing Design - Collapse
2. Calculate D/t to determine proper equation to use for calculating the collapse pressure
Yield Strength Collapse :
Plastic Collapse:

35. Casing Design - Collapse, cont’d
Transition
Collapse:
Elastic Collapse:

36. Casing Design - Collapse
If Axial Tension is Zero:
Yield Strength Plastic Transition Elastic J N P

37. Example 2
Determine the collapse strength of 5 1/2” O.D., #/ft J-55 casing under zero axial load.
1. Calculate
the D/t ratio:

38. Example 2 2. Check the mode of collapse
Table on p.35 (above) shows that,
for J-55 pipe,
with < D/t < 25.01
the mode of failure is plastic collapse.

39. The plastic collapse is calculated from:
Example 2
The plastic collapse is calculated from:
Halliburton Tables rounds off to 3,120 psi

40. Example 3
Determine the collapse strength for a 5 1/2” O.D., #/ft, J-55 casing under axial load of 100,000 lbs
The axial tension will reduce the collapse pressure as follows:

41. The axial tension will reduce the collapse pressure rating to:
Example 3 cont’d
The axial tension will reduce the collapse pressure rating to:
Here the axial load decreased the J-55 rating to an equivalent “J-38.2” rating

42. Example 3 - cont’d
…compared to 3,117 psi with no axial stress!