This document provides information on casing design, including: - The functions of casing such as preventing hole collapse and contamination. - Examples of typical casing strings like surface, intermediate, and production casing. - Design considerations for casing like burst, collapse, and tension ratings. - An example showing the iterative process of designing a casing string to withstand certain burst, collapse and tension requirements over multiple casing joints. The document outlines the basic process and factors involved in designing well casing strings to isolate formations and safely drill to total depth.

1. CASING DESIGN

2. Attention!!
➢ Please note that this presentation is for your understanding the process of
designing casing.
➢ There are any designing updated methods and tools for casing design.
➢ Operators/Companies have their own design methodologies , safety factors
that may defer from this presentation.
➢ There have been many development in casing manufacturing technologies
and their pressure ratings and specs may be superior.
➢ Casing manufacturers provide their own casing tables that may differ due to
material specs and manufacturing technology.
Thank you.

3. Casing
1. Prevent hole from caving
2. Prevent contamination of fresh water sands
3. Prevent water migration to producing formation
4. Confine production to the wellbore
5. Control pressures during drilling
6. Environment for subsurface equipment in producing wells
7. Drilling to total depth (TD)
Casing
Cement

4. Casing Functions
Drive/Conductor pipe
Provides a mud return path
Prevents erosion of ground below rig
Supports the weight of subsequent casing strings
Isolates very weak formations
Surface casing
– Means of installing WH/BOP
– Strong casing seat (close in a well -kick case).
– Protection of fresh water sands
– Provides wellbore stabilization
– WH: Wellhead
– BOP: Blow Out Preventors

5. Surface Casing
1. offshore 150’-300’
( BML: below mudline).
2. Conductor string. 100’ - 1,600’
(BSL; Below Sea Level)
3. Surface pipe. 2,000’ - 4,000’
(BSL)
Diameter Example
16”-60” 30”
16”-48” 20”
8 5/8”-20” 13 3/8”

6. Intermediate/Contingency/ production/Tubing Strings
4. Intermediate String/Line
5. Contingency string/Liner(s)
6. Production String/Liner
7. Tubing String(s)
• Contingency String: Run if drilling
conditions require (HPHT).
• String/Liner: Run as either full casing
string or liner depending on well design.
• Tubing string: Run for well completion( if
required)
7 5/8”-16” 9 5/8”
Diameter Example
9 5/8”-11”. 105/8”
4 1/2”-9 5/8” 7”
2 1/8”- 5”. 2 3/8”

7. Well Configuration (Example)
Drive pipe
Conductor string
Surface pipe
IntermediateString
Production Liner
Hole Size
30”
20”
13 3/8
9 5/8
7
Pipe Size
36”
26”
17 1/2
12 1/4
8 3/4

8. Well Configuration (Example)
Structural casing
Conductor string
Contingency String
(Optional)
Surface pipe
Intermediate String
Production Liner
Structural Pipe/conductor pipe( optional)
250’
1,000’
4,000’
SL

9. Intermediate or protective casing/Liner
– Compete well program to TD/abnormally pressured zone
– Isolation of potentially troublesome formations/zones
– Withstandmud weights to next Csg. seat/TD
Contingency Csg String/Liner
- Run as required as per hazardous drilling conditions (HPHT, Salt/Coal
etc)
➢ Production casing/Liner
– Zonal isolation
o Migration of water to producing zones
o Isolates production zones
– Confines production to wellbore
– Install subsurface completion equipment

10. ➢ Production casing/Liner
– Zonal isolation
o Migration of water to producing zones
o Isolates production zones
– Confines production to wellbore
– Install subsurface completion equipment
Liners Types
– Drilling liners
• Same as Intermediate or protective casing
– Production liners
• Same as production casing
– Tieback liners
• Tie back drilling or production liner to the surface.
• Converts liner to full string of casing

11. Casing Specs
1. Casing Outside Diameter(OD); (e.g. 9 5/8”)
2. Casing Wall Thickness (T); (e.g. 1/2”)
3. Casing Material Grade, (e.g. N-80)
4. Threads and Couplings (TLC) Type, (e.g. API LCSG)
5. Length of each joint (RANGE), (e.g. Range 3)
6. Nominal weight (Avg. wt/ft incl. coupling weight), (e.g. 47 lb./ft)

12. s
e
Grade/yield/Tensile

13. Casing Joints Lengths & Threads
Casing Joint Length:
RANGE 1 16-25 ft
RANGE 2 25-34 ft
RANGE 3 > 34 ft.
Coupling Thread:
API round threads - short ( CSG)
API round thread - long (LCSG )
Buttress (BCSG)
Extreme line (XCSG )
Xtreme Line
Vam
Etc.

14. RecommendedAPI Casing Design Factors
Collapse 1.125
Tension 1.8
Burst 1.1
Required Prrssure
10,000 psi
100,000 lbf
10,000 psi
Design Pressure
11,250 psi
180,000 lbf
11,000 psi
API Design Factor
(Operators may set their own Safety Factors)

15. API Recommendations
Burst
➢ Design for maximum pressure on the inside of the casing.
o Worst case scenario: Empty casing
o No external pressure.
➢ Design Pressure:- Formation pressure at TD
Collapse
➢ Worst case scenario:-,
o No pressure inside the casing,
o Maximum mud weight at casing depth.
➢ Reduction of collapse rating due to weight of casing/liner hanging below.
Tension
➢ worst case:
o No buoyancy effect.
o Weight of casing string.

16. Normal Pore Pressure Abnormal Pore Pressure
0.433 - 0.465 psi/ft gp > normal
Normal
Abnormal
Design Pressure (Formation Pressure)

17. Burst: Reservoir pressure along the wellbore.
Collapse: Hydrostatic pressure (increases with depth)
Tension: Tensile stress *weight of string at top)
STRESS
Tension
Burst
Collapse
Collapse
Tension
Depth

18. Casing Design-Burst
Example
Design a 7” Csg. String to 10,000 ft.
Pore pressure gradient = 0.5 psi/ft
Design factor, Ni=1.1
Burst Design only.
Internal Yield Pressure for pipe
 Internal Yield Pressure for couplings
 Internal pressure leak resistance

19. Formation pressure:-
psi
000
,
5
ft
000
,
10
*
ft
psi
5
.
0
pres =
=
Required pipe internal yield:-
psi
500
,
5
1
.
1
*
000
,
5
N
*
p
p i
res
i =
=
=
Ni = API Design BURST Factor= 1.1
From Casing Tables:-
7”, J-55, 26 lb./ft : BURST Pressure= 4,980 psi
7”, N-80, 23 lb./ft : BURST Pressure= 6,340 psi
7”, N-80, 26 lb./ft. : BURST Pressure= 7,249 psi
Choose N-80 Csg., 23lb/ft > 5500. Psi

20. Collapse Pressure


















−
















−
=
P
A
2
/
1
2
P
A
P
PA
Y
S
5
.
0
Y
S
75
.
0
1
Y
Y
YPA = yield strength of axial stress equivalentgrade, psi
YP = minimum yield strength of pipe, psi
SA = Axial stress, psi (tension is positive)
SA
SA

21. Collapse Example
P
p
A
2
p
A
PA Y
Y
S
5
.
0
Y
S
75
.
0
1
Y


















−








−
=
( )
psi
Area
F
S A
A 820
,
24
012
.
5
5
.
5
4
000
,
100
2
2
=
−
=
=

Axial tension reduces collapse pressure:
psi
216
,
38
000
,
55
000
,
55
820
,
24
5
.
0
000
,
55
820
,
24
75
.
0
1
Y
2
PA
=














−






−
=

22. Designing 9 5/8”Casing
Design: 9 5/8-in Casing.
• Setting Depth= 8,000’
• Mud Weight 12.5 ppg
• Formation pore pressure - 6,000 psi.
• Available Casing :- N-80, all weights.
• API design factors.
• Combination Casing String
• Design for “worst conditions.”

23. API design Factors:
• Tension and Joint Strength: NT = 1.8
• Collapse (from external pressure): Nc= 1.125
• Burst (from internal pressure): Ni = 1.1
Notes:-
1.To design a string of 100,000 lbf, select pipe with Joint strength of 100,000 * 1.8 = 180,000 lbf.
2.Casing tables provide joint strength values with no safety factors.
3.Always check the connection strength when designing casing for tension.
4.Casing tables provide connection strength values with no safety factors.

24. psi
600
,
6
P
1
.
1
*
psi
000
,
6
Factor
Design
*
pressure
pore
P
B
B
=
=
=
severe
less
are
ts
requiremen
collapse
the
hole
the
up
Further
.
bottom
the
at
d
'
req
psi
850
,
5
P
125
.
1
*
000
,
8
*
5
.
12
*
052
.
0
factor
design
*
depth
*
weight
mud
*
052
.
0
P
c
c

=
=
=
Design Burst Pressure: 6,600 psi
Design Collapse Pressure: 5,850 psi
Casing Tables:-
N-80 53.5 Lb./ft Burst = 7930 Psi
Collapse = 6620 Psi
PlainArea = 15.547 Sq in.

25. Design Burst: 6,600 psi
Design Collapse: 5,850 psi
N-80 53.5 Lb./ft satisfy collapse requirements.

26. N-80 47 #/ft
Can be run to depth:
psi
231
,
4
125
.
1
760
,
4
factor
design
pipe
of
pressure
Collapse
Pc =
=
=
ft
509
,
6
5
.
12
*
052
.
0
231
,
4
5
.
12
*
052
.
0
P
h
h
*
5
.
12
*
052
.
0
P
c
1
1
c
=
=
=

=

27. (8,000 - 6,509) = 1,491’ of 53.5 #/ft
The weight of this pipe will reduce the collapse resistance of the 47.0
#/ft pipe!
Weight, W1 = 53.5 #/ft * 1,491 ft = 79,769 lbf
Axial stress in 47 #/ft pipe
psi
877
,
5
in
13.572
lbf
769
,
79
area
end
weight
S
of 2
1 =
=
=
API tables:- stress will reduce the collapse resistance from 4,760 to
somewhere between 4,680 psi (with 5,000 psi stress) and 4,600 psi
(with 10,000 psi stress)
( )
2
1
1
2
1
1
c1
P P
P
S
S
S
S
P −








−
−
−
=

28. Interpolation between these values shows that the collapse resistance at 5,877 psi
axial stress is:
psi
148
,
4
125
.
1
666
,
4
P
psi
666
,
4
)
600
,
4
680
,
4
(
*
)
000
,
5
000
,
10
(
)
000
,
5
877
,
5
(
680
,
4
P
cc1
1
c
=
=
=
−
−
−
−
=
With the design factor,
( )
2
1
1
2
1
1
c1
P P
P
S
S
S
S
P −








−
−
−
=
ft
382
,
6
5
.
12
*
052
.
0
148
,
4
h2 =
=
Which differs considerably from
the initial depth of 6,509 ft, so a
second iteration is required.

29. Run 47 #/ft pipe to 6,382 ft.
psi
378
,
6
in
572
.
13
lbf
563
,
86
S
lbf
563
,
86
5
.
53
*
)
382
,
6
000
,
8
(
W
2
2
2
=
=
=
−
=
( )








−








−
−
−
= 2
1
1
2
1
1
c1
D.F.
1
P P
P
S
S
S
S
P
( ) psi
pcc 140
,
4
600
,
4
680
,
4
*
5000
5000
378
,
6
680
,
4
125
.
1
1
2 =












−
−
−
=
ft
369
,
6
5
.
12
*
052
.
0
140
,
4
h3 =
=
Interpolating
Pressure at depth of:
13 ft short of 6382Ft.

30. psi
429
,
6
572
.
13
259
,
87
S
lbf
259
,
87
5
.
53
*
)
369
,
6
000
,
8
(
W
'
369
,
6
h
3
3
3
=
=
=
−
=
=
Pcc3 = ?
2
3
140
,
4
)
600
,
4
680
,
4
(
*
000
,
5
000
,
5
429
,
6
680
,
4
125
.
1
1
cc
cc
P
psi
P
thus
=
=






−
−
−
=
Run 47 #/ft N-80 to 6,369 ft- Surface.
53.5 #/ft: 6,369 -8,000 ft.
43.5 #/ft pipe?: Do not meet burst requirements.

31. Tension Check
Weight on casing top joint :-
Design factor of 1.8 for tension, a pipe strength of
weight
actual
602
,
386
)
/
#
5
.
53
*
631
,
1
(
)
/
#
0
.
47
*
369
,
6
(
lbs
ft
ft
ft
ft
=
+
required
is
lbf
080
,
695
602
,
386
*
8
.
1 =
surface
to
OK
is
ft
/
#
0
.
47

Casing Tables:-Yield strength of 1,086,000 lbf for pipe body
and a joint strength of 905,000 lbf for LT & C.