Casing Design.pdf

7/25/2019 Casing Design.pdf

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Casing Design

Vamegh Rasouli

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Casing Design - Introduction

What is casing?

Why run casing?1. To prevent the hole from

caving in,

2. Onshore: to preventcontamination of freshwater sands,

3. To prevent watermigration to producingformation,

Casing

Cement


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Casing Design - Why run casing - contd

4. To confine production to the wellbore,

5. To control pressures during drilling,

6. To provide an acceptable environment forsubsurface equipment in producing wells,

7. To enhance the probability of drilling to totaldepth (TD).

e.g., you need 14 ppg to control a lower zone, but anupper zone will fracture at 12 lb/gal.

What to do?

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Typical Sequence of

Csg. Strings


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Functions of Casing Individually

Drive pipe Driven & cemented to

shallow depth in pre-

drilled or pre-dug holes

Provides a mud return

path to surface,

Prevents erosion of

ground below rig.

Conductor pipe Same as Drive pipe,

Supports the weight of next

casing strings,

Isolates very weak

formations.

Diverter installed to shale

shaker Corrosion barrier

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Functions of Casing Individually

Surface casing

Provides a means of

nippling up BOP,

Provides a casing seat

strong enough to safely

close in a well after a

kick,

Provides protection of

fresh water sands,

Provides wellbore

stabilization.

Intermediate casing

Usually set in the first

abnormally pressured

zone,

Provides isolation of

potentially troublesome

zones,

Provides integrity to

withstand the high mud

weights necessary to

reach TD or the next csg.

Seat.


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Functions of Casing Individuallycontd

Production casing Provides zonal isolation

(prevents migration ofwater to producing zonesand isolates differentproduction zones)

Confines production towellbore

Provides the environmentto install subsurfacecompletion equipment

Liners Drilling liners

Same as Intermediatecasing

Production liners Same as production casing

Tieback liners Tie back drilling or

production liner to thesurface. Converts liner tofull string of casing

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Types of Strings of Casing

Diameter Example

1. Drive Pipe or Structural Pile

(Gulf Coast and offshoreonly)

150-300 BML

16-60 30

2. Conductor String

100 - 1,600 BML16-48 20

3. Surface Pipe

2,000 - 4,000 BML85/8-20 13

3/8


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Types of Strings of Casingcontd

Diameter Example

4. Intermediate String 75/8-133/8 9

5/8

5. Production String 4-95/8 7

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Casing Programs


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Casing Programscontd

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Casing Selection

Chart


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Hole Size Pipe Size

36 Conductor casing 30

26 Surface string 20

17 Intermediate pipe 133/8

12 Intermediate String 95/8

77/8 Production Liner 51/2

Example Hole and StringSizes (in)

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Classification of CSG.

Outside diameter of pipe (e.g. 95/8)

Wall thickness (e.g. )

Grade of material (e.g. N-80) Type to threads and couplings (e.g. API LCSG)

Length of each joint (e.g. Range III)

Nominal weight (e.g. 47 lb/ft)


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Most Common Grades Minimum Yield

Strength (KPSI)

Ultimate Tensile

Strength (KPSI)

H-40 40 60

J-55 55 75

K-55 55 95

C-75 75 95

L-80 80 95

N-80 80 100

C-90 90 100

C-95 95 105

P-110 110 125

V-150 150 160

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Length of Casing Joints

RANGELENGTH

(ft)

I 16 - 25

II 25 - 34

III > 34


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Casing Threads and Couplings

API round threadsshort ( CSG )

API round thread - long ( LCSG )

Buttress ( BCSG )

Extreme line ( XCSG )

Other

See Halliburton Book...

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Casing Threads and Couplingscontd

Rounded Threads8 threads per inch4 to 20

Square ThreadsLongerStronger 4 to 20

Integral JointSmaller ID, ODCosts moreStrong 5 to 103/4


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Wellhead & Christmas Tree

Wellhead

Hang Casing Strings

Provide Seals

Christmas Tree

Control Production

from Well

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Wellhead & Christmas Treecontd


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Casing Performance - Uniaxial

Loadings

Axial Tension (couplings & body)

Burst Pressure

Collapse Pressure

Bending Buckling

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Tension Strength/Failure


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Tension Strength

Tension Strength Couplings: API Tables

for various couplings

Body (perm. deform.)

Fy

= pipe body yield strength

D = external diameter (nominal)

d = internal diameter

YP = yield stress

Fy

=

4

D

2 d2

YP

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Tension StrengthExample 1

Compute the body-yield strength for a 7, N-80,

23 lb/ft casing.

Solution:

From API Table (1& 2)D = 7 in

d = 6:366 in

YP

= 80; 000 p si

Fy

=

4

72 6:366

2 80; 00 0 = 532 ksi


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Tension Strength Formula

Uses Nominal Diameter

API minimum Thickness 87.5% of original

(nominal) thickness

Yield Strength

Rupture much larger

May deform plastically

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Burst (Internal Pressure)

Yield the body

Yield the coupling Leak the coupling

P


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Burst (Internal Pressure)

Barlow (API allows 87.5% of thickness)

Thin Wall Assumption

Pbr = pipe body burst pressure

D = nominal diameter

YP = yield stress

Pbr

= 0:8 75

2 Y

Pt

D

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Burst (Internal Pressure)Example 2

Compute the body burst pressure for a 7, N-

80, 23 lb/ft casing.

Solution:

From API TableD = 7 in

d = 6:366 in ! t =7 6:366

2= 0:317 in

YP

= 80; 000 psi

Pbr

= 0:875

2 80; 000 0:317

7

= 6; 340 psi


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Collapse (External Pressure)

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Collapse (External Pressure)contd

The following factors are important:

The collapse pressure resistance of a pipe

depends on the axial stress (biaxial stress) There are different regimes of collapse failure

(depends on ratio D/t) Yield Strength Collapse (thick wall)

Plastic Collapse

Transition Collapse

Elastic Collapse

(Empirical Formulation from API)


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Yield Stress Collapse Pressure (thick wall)

r(r) =

pi

r2i

r2

o

r2

+ po

r2o

r2 r2

i

r2 (r2o r

2i )

t(r) =

pi

r2i

r2

o+ r2

p

or2

o

r2 + r2i

r2 (r2

o r2

i)

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Yield Strength Collapse Pressure

PYp = pipe body collapse pressure


t = wall thickness

YP = yield stress (effective for biaxial stress)

PYP = 2 YP (D =t) 1

(D =t)2


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Plastic Collapse Pressure

PP

= pipe body collapse pressure


t = wall thickness

YP= yield stress (effective for biaxial stress)

A, B, C, F, G,Material (and stress) dependent coefficients

PP

= YP

A

D =t B

C

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Coef.s Formulas (API Bull. 5C3)


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Transition Collapse Pressure

PP

= pipe body collapse pressure


t = wall thickness

YP= yield stress (effective for biaxial stress)

A, B, C, F, G, Material (and stress) dependent coefficients

PT

= YP

F

D =t G

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Elastic Collapse Pressure

PE = pipe body collapse pressure


t = wall thickness

PE =

46:95 106

(D =t) [(D =t) 1]2


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A, B, C, F, G

These values are for the

uniaxial stress

Different values for

effective yield stress

For Biaxial calculate the

effective Yield Stress

and interpolate thecoefficients

(Coef.s depend on Yield Stress)

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(D=t)Y P

=

p(A 2)2 + 8(B + C = Y

P) + (A 2)

2 (B + C = Y P)


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Upper Limit for Plastic Collapse

(D=t)P T

=Y

P(A F )

C + Y P(B G)

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Upper Limit for Transition Collapse

(D=t)T E

=2 + B=A

3 B=A


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Boundaries for Axial Stress = 0

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Collapse (External Pressure)Example 3

Calculate the Collapse pressure rating for a 7 in, N-80, 23

lb/ft casing.

Solution: 7 in, N-80, 23 lb/ft t = 0.317 in

Grade A B C F G

N-80 3.071 0.0667 1,955 1.988 0.0434

(D= t) =7

0:317= 2 2:08 ! Pl as tic collaps e for N80


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Collapse (External Pressure)Example 3

PP

= YP

A

D= t B

C

PP

= 80; 000

3:071

22:08 0:0667

1; 955 = 3; 836 psi

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Effect of Axial Stress in the Collapse

ResistanceEffective Yield Stress

Von Mises Criteria (Distortion Energy) Material fails (ductileyield failure) when totaldistortion energy equals uniaxial test distortion

energy

Triaxial Collapse

(a

t)2 + (

t

r)2 + (

r

a)2

= 2 Y2

P


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Triaxial

Biaxial

Triaxial Collapsecontd

Ye = effective yield stress

YP = uniaxial stresstsa =axial stress

pi = internal pressure (pi


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Coef.s Formulas (API Bull. 5C3)

A = 2:8762 + 0:10679 105 YP

+ 0:21301 1010 Y 2P 0:5 3132 1016 Y 3

P

B = 0:0 2623 3 + 0:506 09 106 YP

C = 465:93 + 0:030867 YP 0:10483 107 Y 2

P+ 0:36989 1013 Y 3

P

F =

46:95 106 h3 B =A

2 + B =A i3

YP

h3B =A

2 + B =A

B =Ai h

13B =A

2 + B =A

i2

G = F B =A

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Triaxial CollapseExample 4

For the casing of Example 3, calculate the

corrected critical collapse pressure if a section of

2,000 ft, 7 in, N-80, 23 lbm/ft casing is

suspended below it (assume linear weight of 23

lbf/ft and empty borehole - no buoyancy effect).

What is the corrected collapse pressure if the

internal pressure is 1,000 psi?


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Solution:

Weight of Casing Below Point in Question

Cross Section Area

Axial Stress

F = 2; 000 23 = 46; 000 lbf

Ac

=

4

72 6:3 6 6

2= 6:6 55 5 i n2

a

=46; 000

6:6555= 6; 9 1 2 psi

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Effective Yield Stress (biaxial)

(an equivalent N-76.32)

Ye

= rY 2P 3

a

2 2 a

2

Ye

=

s80; 0 00

2 3

6; 9 12

2

2 6; 912

2= 76; 3 20 p si


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Interpolated Coef.s

API Fs Formulas (MsExcel Spreadsheet)

Grade A B C F G

C-75 3.054 0.0642 1,806 1.990 0.0418

N-76.32 3.059 0.0649 1,845 1.992 0.0422

N-80 3.071 0.0667 1,955 1.998 0.0434

Yp 76320

A B C F G

3.058 0.0649 1845 1.992 0.0422

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Collapse Regime

Yield Regime U-Limit:

q(3:0 58 2)2 + 8 (0:0649 + 1;8 45

7 6;3 2 0) + (3:058 2 )

2 ( 0:064 9 + 1;8457 6;320

)= 13:5 4 < 22:08

(D = t) =7

0:3 1 7= 2 2:0 8

(D = t)Y P

=

p(A 2)2 + 8(B + C = Y

P) + (A 2)

2 (B + C = YP

)


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Plastic Regime U-Limit:

Collapse occurs in the Plastic Regime


(D= t)P T

=Y

P(A F )

C + YP

(B G)

22:0 8 8,000 ft)

pp= 11,000 x 0.650 = 7,150 psi(1-0,4)xDnc= 6,600 ft

p6600= 7,150-0.052x10.5x6,600=3,546 psi

pi= 3,546 psi


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Casing Design Example contd

Burst Pressurecontd:

F.S. = 1.1

pab= (pi-po)

pab

= 3,5460.52D

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Collapse Loading

External Pressure:

po= 0.52 x D

Internal pressure = 0 psi

F.S. = 1.0

pac= 0.52 x D


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Design for Burst Start at bottom (minimum burst pressure)

pab,4000= 3,5460.52 x 4000 = 1,466 psi

Cheapest casing: (p.320-321)

K-55, 40.50 lb/ft, Burst Strength 3,130 psi

Minimum depth that can go:pab,D= 3,5460.52 x D = 3130 psi / 1.1

Dmin= 1347 ft

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Continue with next cheapest CasingK-55, 45.50 lb/ft, Burst Strength 3,580 psi

Minimum depth that can go:

pab,D= 3,5460.52 x D = 3,580 psi / 1.1

Dmin= 561 ft


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Continue with next cheapest CasingK-55, 51.00 lb/ft, Burst Strength 4,030 psi

Minimum depth that can go:

pab,D= 3,5460.52 x D = 4,030 psi / 1.1

Dmin= -226 ft (above surface)

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0 ft

561 ft

1347 ft

4000 ft

103/4K-55 51.00 lb/ft

103/4K-55 45.50 lb/ft

103/4K-55 40.50 lb/ft

Burst Diagram


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Design for Collapse (uniaxial)

Start at top (minimum collapse pressure)

pac= 0.52 x D

Cheapest casing:

K-55, 40.50 lb/ft, Collapse Strength 1,580 psi

Maximum depth that can go:pac,D= 0.52 x D = 1,580 psi / 1.0

Dmax= 3,038 ft

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Continue with next cheapest CasingK-55, 45.50 lb/ft, Collapse Strength 2,090 psi

Maximum depth that can go:

pac,D= 0.52 x D = 2,090 psi / 1.0

Dmax= 4.019 ft


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0 ft

3038 ft

4000 ft

103/4K-55 45.50 lb/ft

103/4K-55 40.50 lb/ft

Collapse Diagram

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Combine Two Diagrams

0 ft

561 ft

1347 ft

4000 ft

3038 ft

+ =

103/4K-55 51.00 lb/ft

103/4K-55 45.50 lb/ft

103/4K-55 40.50 lb/ft

103/4K-55 45.50 lb/ft

collapse

burst

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