casing-design for drilling engineering-2005.ppt

PETE 203
DRILLING ENGINEERING
CASING DESIGN

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

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” 30”
16”-48” 20”
8 5/8”-20” 13 3/8”

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”

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

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

casing-design for drilling engineering-2005.ppt

CONDUCTOR (1 or 2) (40’ – 300’)
 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' - 5000')
 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.

INTERMEDIATE CSG (1 or 2)
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.

PRODUCTION CSG
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.

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

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)

Length of Casing Joints
RANGE 1 16-25 ft
RANGE 2 25-34 ft
RANGE 3 > 34 ft.

 OUTSIDE DIAMETER (4.5 -20")
 Tolerance 0.75%
 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.

 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.

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.

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

 CSG & LCSG
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.

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.

 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.

 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 0.005 on a
standard test specimen.
 Minimum yield strength = 80% of average yield
strength observed.

Grades of Casing Recognized by the API

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 0.635
in. and a nominal weight
per foot of 133 lbf/ft.
A
*
F s
yield
ten s


Solution:
This pipe has a minimum
yield strength of 55,000 psi
and an ID of:
.
in
730
.
18
)
635
.
0
(
2
00
.
20
d 


K55
A
*
F s
yield
ten s


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:
.
in
.
sq
63
.
38
)
73
.
18
20
(
4
A 2
2
s 



lbf
000
,
125
,
2
)
63
.
38
(
000
,
55
Ften 

A
*
F s
yield
ten s


Pipe Body Yield Strength
where
p
2
2
y Y
)
d
D
(
4
P 


in
pipe,
of
diameter
inside
d
in
pipe,
of
diameter
outside
D
psi
strength,
yield
minimum
specified
Y
lbf
strength,
yield
body
pipe
P
p
y





Pipe Body Yield Strength
Example
What is yield strength of body of 7”, 26 #/ft,
P-110 casing?
p
2
2
y Y
)
d
D
(
4
P 


lbf
402
,
830
000
,
110
)
276
.
6
7
(
4
P 2
2
y 



lbf
000
,
830
Py  (to the nearest 1,000 lbf).
…agrees with Tables

Internal Yield Pressure for Pipe (Burst)
where







D
t
Y
2
875
.
0
P p
in
pipe,
of
O.D.
D
in
thickness,
wall
nominal
t
psi
strength,
yield
minimum
Y
psi
pressure,
yield
internal
P
p




FP = DLP
FT = 2tLYP
DLP = 2tLYP







D
t
2Y
P p
FP
FT

Example
For 7”, 26 #/ft P-110 pipe
9,955
7
*
2
6.276)
-
(7
*
110,000
*
2
*
0.875


psi
960
,
9
P  (to the nearest 10 psi)
…agrees with Tables.







D
t
Y
2
875
.
0
P p

TABLE 7.8 –COMMONLY USED BIT SIZES THAT WILL PASS THROUGH API CASING
Casing
Size
(O.D., in)
Weight
Per Foot
(lbm/ft)
Internal
Diameter
(in.)
Drift
Diameter
(in.)
Commonly
Used
Bit Sizes
(in.)
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
3 7/8

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

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.

Burst Example
1. Calculate probable reservoir pressure.
psi
000
,
5
ft
000
,
10
*
ft
psi
5
.
0
pres 

2. Calculate required pipe internal yield
pressure rating
psi
500
,
5
1
.
1
*
000
,
5
N
*
p
p i
res
i 



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

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

Table 3
Grade D/t Ratio
H40 16.44 and less
J & K55 14.8 and less
C75 13.67 and
N80 13.38 and less
C95 12.83 and less
P105 12.56 and less
P110 12.42 and less
 
   
 
2
/
/
1
/
2 t
D
t
D
Ym
c 

 (4)

casing-design for drilling engineering-2005.ppt

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casing-design for drilling engineering-2005.ppt