Download - 10 Casing Design
-
7/30/2019 10 Casing Design
1/78
1
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
-
7/30/2019 10 Casing Design
2/78
2
Casing
Cement
What is casing?
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
Casing Design
-
7/30/2019 10 Casing Design
3/78
3
Why run casing?
4. To confine production to the wellbore
5. To control pressures during drilling
6. To provide an acceptable environment for subsurfaceequipment in producing wells
7. To enhance the probability of drilling to total depth(TD)
-
7/30/2019 10 Casing Design
4/78
4
Example Hole and String Sizes (in)
Structural casing
Conductor string
Surface pipe
Intermediate String
Production Liner
Hole Size
30
20
133/8
9 5/8
7
Pipe Size
36
26
171/2
121/4
e.g., you need 14 ppg to control a lower zone, but an upper zonewill fracture at 12 lb/gal.
What do you do?
-
7/30/2019 10 Casing Design
5/78
5
Diameter Example
16-60 30
16-48 20
8 5/8-20 13 3/8
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
(BML)
Types of Strings of Casing
-
7/30/2019 10 Casing Design
6/78
6
Types of Strings of Casing
4. Intermediate String
5. Production String (Csg.)
6. Liner(s)
7. Tubing String(s)
Diameter Example
4. Intermediate String
5. Production String (Csg.)
6. Liner(s)
7. Tubing String(s)
7 5/8-13 3/8 9 5/8
4 1/2-9 5/8 7
-
7/30/2019 10 Casing Design
7/78
7
Example Hole and String Sizes (in)
Structural casing
Conductor string
Surface pipe
Intermediate String
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
-
7/30/2019 10 Casing Design
8/78
8
Example Hole and String Sizes (in)
Structural casing
Conductor string
Surface pipe
Intermediate String
Production Liner
250
1,000
4,000
Mudline
-
7/30/2019 10 Casing Design
9/78
9
Classification of Casing
1. Outside diameter of pipe (e.g. 9 5/8)
2. Grade of material (e.g. N-80)
3. Nominal weight (Avg. wt/ft incl. Wt. Coupling)
(e.g. 47 lb/ft)
4. Type to threads and couplings (e.g. API LCSG)5. Length of each joint (RANGE) (e.g. Range 3)
-
7/30/2019 10 Casing Design
10/78
10
se
-
7/30/2019 10 Casing Design
11/78
11
Length of Casing Joints
RANGE 1 16-25 ft
RANGE 2 25-34 ft
RANGE 3 > 34 ft.
-
7/30/2019 10 Casing Design
12/78
12
Casing Threads and Couplings
API round threads - short { CSG }
API round thread - long { LCSG }
Buttress { BCSG }
Extreme line { XCSG } Other
See Halliburton Book...
-
7/30/2019 10 Casing Design
13/78
13
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
-
7/30/2019 10 Casing Design
14/78
14
Normal Pore Pressure Abnormal Pore Pressure
0.433 - 0.465 psi/ft gp > normal
Abnormal
-
7/30/2019 10 Casing Design
15/78
15Design from bottom
-
7/30/2019 10 Casing Design
16/78
16
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
Casing Design
STRESS
Tension
Burst
Collapse
Collapse
Tension
Depth
Burst
-
7/30/2019 10 Casing Design
17/78
17
Casing Design
Collapse (from external pressure)
Yield Strength Collapse
Plastic Collapse
Transition Collapse
Elastic Collapse
Collapse pressure is affected by axial stress
-
7/30/2019 10 Casing Design
18/78
18
Casing Design - Collapse
-
7/30/2019 10 Casing Design
19/78
19
Casing Design - Tension
-
7/30/2019 10 Casing Design
20/78
20
Casing Design - Burst
p pInternalPressure
Internal Yield Pressure for pipe
Internal Yield Pressure for couplings
Internal pressure leak resistance
-
7/30/2019 10 Casing Design
21/78
21
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.
-
7/30/2019 10 Casing Design
22/78
22
Burst Example
1. Calculate probable reservoir pressure.
2. Calculate required pipe internal yield pressure rating
-
7/30/2019 10 Casing Design
23/78
23
Burst Example
3. Select the appropriate csg. grade and wt. from theHalliburton 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 psi7, N-80, 26 lb/ft has BURST Rating of 7,249 psi
Use N-80 Csg., 23 lb/ft
-
7/30/2019 10 Casing Design
24/78
24
-
7/30/2019 10 Casing Design
25/78
25
23 lb/ft
26 lb/ft
N-80
-
7/30/2019 10 Casing Design
26/78
26
Collapse Pressure
The following factors are important:
The collapse pressure resistance of apipe depends on the axial stress
There are different types of collapsefailure
-
7/30/2019 10 Casing Design
27/78
27
Collapse Pressure
There are four different types of collapsepressure, each with its own equation for
calculating the collapse resistance:
Yield strength collapse
Plastic collapse
Transition collapse
Elastic collapse
-
7/30/2019 10 Casing Design
28/78
28
Casing Design
YPA = yield strength of axial stress
equivalent grade, psiYP = minimum yield strength of pipe, psi
SA = Axial stress, psi (tension is positive)
Collapse pressure - with axial stress
1.
P
A
P
A
PPA Y
S
Y
SYY 5.075.01
2/12
-
7/30/2019 10 Casing Design
29/78
29
Casing Design2. Calculate D/t to determine proper equation
to use for calculating the collapse pressure
Yield StrengthCollapse :
Plastic Collapse:
2
1
2
t
D
t
D
YP pYP
CB
t
D
AYP pp
-
7/30/2019 10 Casing Design
30/78
30
Casing Design
Transition
Collapse:
ElasticCollapse:
G
tD
FYP pT
2
6
E
1t
D
t
D
10X95.46P
-
7/30/2019 10 Casing Design
31/78
31
Casing Design - Collapse
If Axial Tension is Zero:
Yield Strength Plastic Transition Elastic
J-55 14.81 25.01 37.31
N-80 13.38 22.47 31.02P-110 12.44 20.41 26.22
-
7/30/2019 10 Casing Design
32/78
32
Example 2
Determine the collapse strength of 5 1/2O.D., 14.00 #/ft J-55 casing under zero axialload.
1. Calculate
the D/t ratio:
-
7/30/2019 10 Casing Design
33/78
33
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
-
7/30/2019 10 Casing Design
34/78
34
Example 2
The plastic collapse is calculated from:
psi117,3Pp Halliburton Tablesrounds off to 3,120 psi
-
7/30/2019 10 Casing Design
35/78
35
Example 3
Determine the collapse strength for a 5 1/2 O.D.,14.00 #/ft, J-55 casing under axial load of 100,000lbs
The axial tension will reduce the collapse pressure asfollows:
P
p
A
2
p
APA Y
Y
S5.0
Y
S75.01Y
-
7/30/2019 10 Casing Design
36/78
36
Example 3
Here the axial load decreased the J-55 ratingto an equivalent J-38.2 rating
P
p
A
p
APA Y
Y
S
Y
SY
5.075.01
2
The axial tension will reduce the collapse pressure rating to:
-
7/30/2019 10 Casing Design
37/78
37
Example 3
psi550,2Pp
compared to 3,117 psi with no axial stress!
-
7/30/2019 10 Casing Design
38/78
38
Casing Design Example
Example Problem
API Design Factors
Worst Possible Conditions
Effect of Axial Tension on Collapse Strength
Iteration and Interpolation
Design for Burst, Collapse and Tension
-
7/30/2019 10 Casing Design
39/78
39
Casing Design Example
Design a 9 5/8-in., 8,000-ft combinationcasing string for a well where the mud wt.will be 12.5 ppg and the formation porepressure is expected to be 6,000 psi.
Only the grades and weights shown areavailable (N-80, all weights). Use APIdesign factors.
Design for worst possible conditions.
-
7/30/2019 10 Casing Design
40/78
40
Casing Design
Before solving this problem is it necessary tounderstand what we mean by DesignFactors and worst possible conditions.
API Design Factors
Design factors are essentially safety factorsthat allow us to design safe, reliable casing
strings. Each operator may have his own setof design factors, based on his experience,and the condition of the pipe.
-
7/30/2019 10 Casing Design
41/78
41
Casing Design
Well use the design factors recommended by theAPI unless otherwise specified.
These are the API design Factors:
Tension and Joint Strength: NT
= 1.8
Collapse (from external pressure): Nc= 1.125
Burst (from internal pressure): Ni = 1.1
-
7/30/2019 10 Casing Design
42/78
42
Casing Design
What this means is that, for example, if weneed to design a string where the maximumtensile force is expected to be 100,000 lbf,
we select pipe that can handle 100,000 * 1.8 =180,000 lbf in tension.
Note that the Halliburton Cementing Tables listactual pipe strengths, without safety factorsbuilt in.
-
7/30/2019 10 Casing Design
43/78
43
Casing Design
Unless otherwise specified in a particularproblem, we shall also assume the following:
Worst Possible Conditions1. For Collapse design, assume that the casing is
empty on the inside (p = 0 psig)
2. For Burst design, assume no backup fluid onthe outside of the casing (p = 0 psig)
-
7/30/2019 10 Casing Design
44/78
44
Casing DesignWorst Possible Conditions, contd
3. For Tension design,assume no buoyancy effect
4. For Collapse design,assume no buoyancy effect
The casing string must be designed to stand up to theexpected conditions in burst, collapse and tension.Above conditions are quite conservative. They are alsosimplified for easier understanding of the basic
concepts.
-
7/30/2019 10 Casing Design
45/78
45
Casing Design
Burst Requirements (based on the expected pore pressure)
The whole casing string must be capable of withstanding thisinternal pressure without failing in burst.
Dep
th
Pressure
-
7/30/2019 10 Casing Design
46/78
46
Casing Design
Collapse Requirements
For collapse design, we start at the bottom ofthe string and work our way up.
Our design criteria will be based on hydrostaticpressure resulting from the 12.5 ppg mud that
will be in the hole when the casing string isrun, prior to cementing.
-
7/30/2019 10 Casing Design
47/78
47
Casing Design
Collapse Requirements, contd
severelessare
tsrequiremencollapsetheholetheupFurther
bottomtheatdreqpsiP
factordesigndepthweightmudP
c
c
.'850,5
125.1*000,8*5.12*052.0***052.0
Depth
Pressure
-
7/30/2019 10 Casing Design
48/78
48
Casing Design Reqd: Burst: 6,600 psi Collapse: 5,850 psi
-
7/30/2019 10 Casing Design
49/78
49
Casing Design
Note that two of the weights of N-80 casingmeet the burst requirements, but only the53.5 #/ft pipe can handle the collapse
requirement at the bottom of the hole (5,850psi).
The 53.5 #/ft pipe could probably run all theway to the surface (would still have to checktension), but there may be a lower costalternative.
-
7/30/2019 10 Casing Design
50/78
50
Casing Design
To what depth might we be ableto run N-80, 47 #/ft? The
maximum annular pressurethat this pipe may be exposedto, is:
Depth
Pressure
-
7/30/2019 10 Casing Design
51/78
51
Casing Design
First Iteration
At what depth do we see this pressure (4,231 psig)in a column of 12.5 ppg mud?
-
7/30/2019 10 Casing Design
52/78
52
Casing Design
This is the depth to which the pipecould be run if there were
no axial stress in the pipe
But at 6,509 we have (8,000 - 6,509) = 1,491 of 53.5#/ft pipe below us.
The weight of this pipe will reduce the collapseresistance of the 47.0 #/ft pipe!
8,000
6,509
-
7/30/2019 10 Casing Design
53/78
53
Casing Design
Weight, W1 = 53.5 #/ft * 1,491 ft= 79,769 lbf
This weight results in an axial stress inthe 47 #/ft pipe
-
7/30/2019 10 Casing Design
54/78
54
Casing Design
The API tables show that the above stresswill 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)
-
7/30/2019 10 Casing Design
55/78
55
Casing DesignInterpolation between these values shows that the
collapse resistance at 5,877 psi axial stress is:
With the design factor,
2112
11c1P PPSS
SS
P
-
7/30/2019 10 Casing Design
56/78
56
Casing Design
This (4,148 psig) is the pressure at a depth
Which differs considerably from the initialdepth of 6,509 ft, so a second iteration is
required.
-
7/30/2019 10 Casing Design
57/78
57
-
7/30/2019 10 Casing Design
58/78
58
-
7/30/2019 10 Casing Design
59/78
59
Casing Design
Second Iteration
Now consider running the 47 #/ftpipe to the new depth of 6,382 ft.
-
7/30/2019 10 Casing Design
60/78
60
Casing DesignInterpolating again,
This is the pressure at a depth of
21
12
11c1
D.F.
1P PP
SS
SSP
-
7/30/2019 10 Casing Design
61/78
61
Casing Design
This is within 13 ft of the assumed value. If moreaccuracy is desired (generally not needed), proceedwith the:
Third Iteration
Pcc3 = ?
-
7/30/2019 10 Casing Design
62/78
62
Casing Design
Third Iteration, contd
-
7/30/2019 10 Casing Design
63/78
63
Casing Design
Third Iteration, contd
This is the answer we are looking for, i.e., we canrun 47 #/ft N-80 pipe to a depth of 6,369 ft,
and 53.5 #/ft pipe between 6,369 and 8,000 ft.
Perhaps this string will run all the way to the
surface (check tension), or perhaps an even moreeconomical string would include some 43.5 #/ftpipe?
-
7/30/2019 10 Casing Design
64/78
64
Casing Design
At some depth the 43.5 #/ft pipe would beable to handle the collapse requirements,but we have already determined that it willnot meet burst requirements.
-
7/30/2019 10 Casing Design
65/78
65
N-8053.5 #/ft
N-8047.0 #/ft
N-8043.5 #/ft?
Depth = 5,057?5,066?5,210?
Depth = 6,369
6,3696,3826,509
8,000
Burst?
Casing Design
-
7/30/2019 10 Casing Design
66/78
66
Tension Check
The weight on the top joint of casing would be
With a design factor of 1.8 for tension, a pipestrength of
-
7/30/2019 10 Casing Design
67/78
67
Tension Check
The Halliburton cementing tables give a yieldstrength of 1,086,000 lbf for the pipe body
and a joint strength of 905,000 lbf for LT & C.
-
7/30/2019 10 Casing Design
68/78
68
Casing DesignReviewWe have 4 different weights of casing available to
us in this case:
1. Two of the four weights are unacceptable
to us everywhere in the string becausethey do not satisfy the burstrequirements.
2. Only the N-80, 53.5 #/ft pipe is capable ofwithstanding the collapserequirementsat the bottom of the string
-
7/30/2019 10 Casing Design
69/78
69
Casing DesignReview3. Since the 53.5 #/ft pipe is the most
expensive, we want to use as little of itas possible, so we want to use as
much 47.0 #/ft pipe as possible.
4. Dont forget to check to make sure the
tension requirements are met; both forpipe body, and for threads andcouplings (T&C).
-
7/30/2019 10 Casing Design
70/78
70
Casing DesignReviewThe collapse resistance of N-80, 47 #/ft will
determine to what depth it can be run. Twofactors will reduce this depth:
Design Factor Axial Stress (tension)
Halliburton collapse resistance: 4,760 psi Apply design factor:
-
7/30/2019 10 Casing Design
71/78
71
Casing DesignReviewTo determine the effect of axial stress
requires an iterative process:
1. Determine the depth capability withoutaxial stress
2. Determine axial stress at this point
-
7/30/2019 10 Casing Design
72/78
72
Casing DesignReview3. Determine corresponding collapse resistance
4. Determine depth where this pressure exists
5. Compare with previous depth estimate6. Repeat steps 2-6 using the new depth estimate
7. When depths agree, accept answer(typically 2-4 iterations) (agreement towithin 30 ft will be satisfactory)
-
7/30/2019 10 Casing Design
73/78
73
Linear Interpolation
-
7/30/2019 10 Casing Design
74/78
74
Linear Interpolation
-
7/30/2019 10 Casing Design
75/78
75
Linear Interpolation
With design factor:
21
12
1
1ccPP
SS
SSP
.F.D
1P
-
7/30/2019 10 Casing Design
76/78
76
-
7/30/2019 10 Casing Design
77/78
77
-
7/30/2019 10 Casing Design
78/78
Question
A combination production casing string is toconsider of 15.5 #/ft and 17 #/ft, J-55casing to a total depth of 6300 and is to
be run in 12 ppg mud. Determine the depthat which the casing weight per foot shouldchange because of collapse-pressureconsiderations with a design factor of1.125, assuming that the fluid level couldfall down as low as 6300 in subsequentdrilling operations.