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PETE 411 Well Drilling

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PETE 411Well Drilling

Lesson 17Casing Design

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

Read Applied Drilling Engineering, Ch.7

HW #9 Due 10-18-02

Casing Design

What is casing?

Casing

Cement

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 - 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?

Types of Strings of Casing

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

Diameter Example

7 5/8”-13 3/8” 9 5/8”

4 1/2”-9 5/8” 7”

4. Intermediate String

5. Production String (Csg.)

6. Liner(s)

7. Tubing String(s)

Example Hole and String Sizes (in)

Hole Size

Pipe Size

36”

26”

17 1/2

12 1/4

8 3/4

Structural casing

Conductor string

Surface pipe

IntermediateString

Production Liner

30”

20”

13 3/8

9 5/8

7

Example Hole and String Sizes (in)

Hole Size

Pipe Size

36”

26”

17 1/2

12 1/4

8 3/4

Structural casing

Conductor string

Surface pipe

IntermediateString

Production Liner

30”

20”

13 3/8

9 5/8

7

Example Hole and String Sizes (in)

Structural casing

Conductor string

Surface pipe

IntermediateString

Production Liner

Mudline

250’

1,000’

4,000’

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)

s

e

Length of Casing Joints

RANGE 1 16-25 ft

RANGE 2 25-34 ft

RANGE 3 > 34 ft.

Casing Threads and Couplings

API round threads - short { CSG }

API round thread - long { LCSG }

Buttress { BCSG }

Extreme line { XCSG }

Other …

See Halliburton Book...

API Design Factors (typical)

Required

10,000 psi

100,000 lbf

10,000 psi

Design

11,250 psi

180,000 lbf

11,000 psi

Collapse 1.125

Tension 1.8

Burst 1.1

Abnormal

Normal Pore Pressure Abnormal Pore Pressure 0.433 - 0.465 psi/ft gp > normal

Design from bottom

Press. Gauge

X-mas Tree

Wing Valve

Choke Box

Master

Valves

- Wellhead
- Hang Csg. Strings
- Provide Seals
- Control Production from Well

Wellhead

Wellhead

Tension

Casing Design

Tension

Depth

Burst

Collapse

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

Collapse

STRESS

Burst

Casing Design

Collapse(from external pressure)

Yield Strength Collapse

Plastic Collapse

Transition Collapse

Elastic Collapse

Collapse pressure is affected by axial stress

Casing Design - Collapse

Casing Design - Tension

Casing Design - Burst(from internal pressure)

Internal Yield Pressure for pipe

Internal Yield Pressure for couplings

Internal pressure leak resistance

Internal Pressure

p

p

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.

2. Calculate required pipe internal yield

pressure rating

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

23 lb/ft

26 lb/ft

N-80

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

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

Casing Design

Collapse pressure - with axial stress

1.

YPA= yield strength of axial stress equivalent grade, psi

YP= minimum yield strength of pipe, psi

SA= Axial stress, psi (tension is positive)

Casing Design - Collapse

Yield Strength Collapse :

Plastic Collapse:

2. Calculate D/t to determine proper equation to use for calculating the collapse pressure

Casing Design - Collapse, cont’d

Transition

Collapse:

Elastic Collapse:

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 31.02

P-110 12.44 20.41 26.22

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:

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.

Example 2

The plastic collapse is calculated from:

Halliburton Tables rounds off to 3,120 psi

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:

Example 3 cont’d

The axial tension will reduce the collapse pressure rating to:

Here the axial load decreased the J-55 rating to an equivalent “J-38.2” rating

Example 3 - cont’d

…compared to 3,117 psi with no axial stress!