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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 Example
3
Read Applied Drilling Engineering, Ch.7
HW #9 Due 10-18-02
4
Casing Design
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
What is casing? Casing
Cement
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
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’ (BML)
Diameter Example
16”-60” 30”
16”-48” 20”
8 5/8”-20” 13 3/8”
7
Types of Strings of Casing
4. Intermediate String
5. Production String (Csg.)
6. Liner(s)
7. Tubing String(s)
7 5/8”-13 3/8” 9 5/8”
Diameter Example
4 1/2”-9 5/8” 7”
8
Example Hole and String Sizes (in)
Structural casing
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
9
Example Hole and String Sizes (in)
Structural casing
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
10
Example Hole and String Sizes (in)
Structural casing
Conductor string
Surface pipe
IntermediateString
Production Liner
250’
1,000’
4,000’
Mudline
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
13
Length of Casing Joints
RANGE 1 16-25 ft
RANGE 2 25-34 ft
RANGE 3 > 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)
Collapse 1.125
Tension 1.8
Burst 1.1
Required
10,000 psi
100,000 lbf
10,000 psi
Design
11,250 psi
180,000 lbf
11,000 psi
16
Normal Pore Pressure Abnormal Pore Pressure 0.433 - 0.465 psi/ft gp > normal
Abnormal
17Design from bottom
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X-mas TreeWing Valve
Choke Box
MasterValves
Wellhead
• Hang Csg. Strings• Provide Seals• Control Production
from Well
Press. Gauge
19
Wellhead
20
Wellhead
21
Casing Design
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
STRESS
Tension
Burst
Collapse
Collapse
Tension
Depth
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
p pInternal Pressure
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
Burst Example
1. Calculate probable reservoir pressure.
psi 000,5 ft000,10*ft
psi5.0pres
2. Calculate required pipe internal yield pressure rating
psi 500,51.1 *000,5N *pp iresi
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
29
30
23 lb/ft26 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
Casing Design
Collapse pressure - with axial stress
1.
P
A
2/12
P
APPA Y
S5.0
Y
S75.01YY
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:
2pYP
tD
1tD
Y2P
CB
tDA
YP pp
35
Transition
Collapse:
Elastic Collapse:
G
tDF
YP pT
2
6
E
1tD
tD
10X95.46P
Casing Design - Collapse, cont’d
36
If Axial Tension is Zero:
Yield Strength Plastic Transition Elastic
)t/D(
J-55 14.81 25.01 37.31
N-80 13.38 22.47 31.02
P-110 12.44 20.41 26.22
Casing Design - Collapse
37
Example 2
Determine the collapse strength of 5 1/2” O.D., 14.00 #/ft J-55 casing under zero axial load.
1. Calculate
the D/t ratio:
book nHalliburto From
54.22012.5500.5
21
500.5
t
D
38
Example 2
2. Check the mode of collapse
Table on p.35 (above) shows that,
for J-55 pipe,
with 14.81 < D/t < 25.01
the mode of failure is plastic collapse.
54.22t
D
39
Example 2
The plastic collapse is calculated from:
206,10541.054.22
991.2000,55
CBt/D
AYP pp
psi117,3Pp Halliburton Tables rounds off to 3,120 psi
40
Example 3
Determine the collapse strength for a 5 1/2” O.D., 14.00 #/ft, J-55 casing under axial load of 100,000 lbs
The axial tension will reduce the collapse pressure as follows:
Pp
A
2
p
APA Y
Y
S5.0
Y
S75.01Y
psi
Area
FS A
A 820,24012.55.5
4
000,100
22
41
Example 3 cont’d
The axial tension will reduce the collapse pressure rating to:
psi 216,38
000,55000,55
820,245.0
000,55
820,2475.01Y
2
PA
Here the axial load decreased the J-55 rating to an equivalent “J-38.2” rating
Pp
A
p
APA Y
Y
S
Y
SY
5.075.01
2
42
Example 3 - cont’d
551,243.70010x557.454.22
945.2216,38
CBt/D
AYP
2
PAp
psi 550,2Pp
…compared to 3,117 psi with no axial stress!
43
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