270984243 Casing Design Calculation PDF

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casing design...

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Casing Design Example The table below is a data set from a real land well. As a drilling engineer you are required to calculate the burst and collapse loads that would be used to select an appropriate weight and grade of casing for the Surface, Intermediate and Production strings in this land well:

Assumptions:

Production test data:

Gas density above 10000ft

: 0.1 psi/ft

Well test completion fluid density

:

8.60 ppg.

Design factor (Burst)

: 1.1

Test packer depth

:

11000 ft TVD RKB

Design factor (Collapse)

: 1.0

Test perforation depth

:

11250 ft TVD RKB

Pressure at top of perforation

:

14.0 ppg.

Well test shut-in fluid gradient

:

10.15 psi/ft

Gas lift may be required

Surface Casing (20" @ 3000 ft) From the Drilling Program it can be seen that the following data is to be used for the design: Casing size Setting depth

: :

20" 3000

Pore pressure above 3000 

:

8.6

ppg.

Mud Weight in w hich the casing is to be run

:

9.0

ppg.

Depth of next 17 7½" hole

:

6000

Max. pore pressu ure at bottom of 17½" hole

:

9.5

ppg.

Frac. pressure gradient at the 20" shoe

:

13

ppg.

0.1

psi/

Expected gas graadient





Design Factors: Burst

:

1.1

Collapse

:

1.0

Burst Design - Drilling Internal Load: Assuming that an influx of gas has occurred and the well is full of gas to surface.

Pore pressure at bottom of 17½" hole

= =

Pressure at surface = Pressure at bottom of 17½" = hole - pressure due to column of gas = Pressure at 20" casing shoe

LOT pressure at 20" casing shoe

9.5 x 6000 2964 psi

2964 - (0.1 x 6000) 2364

psi

=

2961 - (0.1 x 3000)

=

2664

= =

psi

13 x 0.052 x 3000 2028

psi

The formation at the casing shoe will breakdown at 2028 psi and therefore it will breakdown if the pressure of 2664 psi is applied to it. The maximum pressure inside the surface casing at the shoe will therefore be 2028 psi. The maximum pressure at surface will be equal to the pressure at the shoe minus a column of gas to surface: =

2028 - (0.1 x 3000)

=

1728

psi

External Load: Assuming that the pore pressure is acting at the casing shoe and zero pressure at surface. Pore pressure at the casing shoe

External pressure at surface Line up against equals Summary of burst loads

=

8.6 x 0.052 x 3000

=

1342

psi

=

0

psi

Collapse Design - Drilling Internal Load: Assuming that the casing is totally evacuated due to losses of drilling fluid.

Internal pressure at surface

=

0

psi

Internal pressure at shoe

=

0

psi

External Load: Assuming that the pore pressure is acting at the casing shoe and zero pressure at surface.

Summary of collapse loads

Intermediate Casing (13⅜" @ 6000 ft) From the Drilling Program it can be seen that the following data is to be used for the design: Casing size

:

13⅜"

Setting depth

:

6000

Minimum pore p ressure above 6000 

:

8.6

ppg.

Maximum pore pressure above 6000  Mud Weight in w hich the casing is to be run

: :

9.5 11.0

ppg. ppg.

Depth of next 12 2¼" hole

:

10000

Max. pore pressu ure at bottom of 12¼" hole

:

11.0

ppg.

Frac. pressure gradient at the 13⅜" shoe

:

16

ppg.

0.1

psi/

Expected gas graadient





Design Factors: Burst

:

1.1

Collapse

:

1.0

Burst Design - Drilling Internal Load: Assuming that an influx of gas has occurred and the well is full of gas to surface.

Pore pressure at bottom of 12¼" hole

= =

Pressure at surface = Pressure at bottom of 12¼" = hole - pressure due to column of gas = Pressure at 13⅜" casing shoe

LOT pressure at 13⅜" casing shoe

11 x 0.052 x 10000 5720 psi

5720 - (0.1 x 10000) 4720

psi

=

5720 - (0.1 x 4000)

=

5320

= =

psi

16 x 0.052 x 6000 4992

psi

The formation at the casing shoe will therefore breakdown when the well is closed in after the gas has flowed to surface. The maximum pressure inside the casing at the shoe will be 4992 psi. The maximum pressure at surface will be equal to the pressure at the shoe minus a column of gas to surface: =

4992 - (0.1 x 6000)

=

4392

psi

External Load: Assuming that the minimum pore pressure is acting at the casing shoe and zero pressure at surface. Pore pressure at the casing shoe

= =

External pressure at surface

=

Summary of burst load

8.6 x 0.052 x 6000 2684 psi 0

psi

Collapse Design - Drilling Internal Load: Assuming that the casing is totally evacuated due to losses of drilling fluid.

Internal pressure at surface

=

0

psi

Internal pressure at shoe

=

0

psi

External Load: Assuming that the maximum pore pressure is acting at the casing shoe and zero pressure at surface. Pore pressure at the casing shoe

= =

External pressure at surface

=

Summary of collapse loads

9.5 x 0.052 x 6000 2964 psi 0

psi

Production Casing (9⅝" @ 10000 ft) From the Drilling Program it can be seen that the following data is to be used for the design: Casing size

:

9⅝"

Setting depth

:

10000



Top of 7" liner

:

9500



Test perforation depth Pressure at top of perforation

: :

11250 14.0

 ppg.

Minimum pore p ressure above 10000  Maximum pore pressure above 10000 

: :

9.5 11.0

ppg. ppg.

Mud Weight in w hich the casing is to be run

:

14.0

ppg.

Density of completion/packer fluid Packer depth

: :

8.6 11000

ppg. 

0.15

psi/

Expected gas graadient Design Factors: Burst

:

1.1

Collapse

:

1.0

Burst Design - Production Internal Load: Assuming that a leak occurs in the tubing at surface and that the Closed In Tubing Head Pressure (CITHP) is acting on the inside of the top of the casing. This pressure will then act on the column of packer fluid. The 9⅝" casing is only exposed to these pressure down to the Top Of Liner (TOL). The 7" liner protects the remainder of the casing.

Max. pore pressure at the top of the production = zone = CITHP (at surface) - Pressure at top of prefs pressure due to column of gas (0.15 psi/)

14 x 0.052 x 11250 8190

psi

=

8190 - 0.15 x 11250

=

6503

psi

External Load: Assuming that the minimum pore pressure is acting at the liner depth and zero pressure at surface. Pore pressure at the top of liner

External pressure at surface

Summary of burst loads

=

9.5 x 0.052 x 9500

=

4693

psi

=

0

psi

Collapse Design - Drilling Internal Load: Assuming that the casing is totally evacuated due to gaslifting operations.

Internal pressure at surface

=

0

psi

Internal pressure at top of liner (TOL)

=

0

psi

External Load: Assuming that the maximum pore pressure is acting on the outside of the casing at the TOL. Pore pressure at the TOL = 11 x 0.52 x 9500 =

Summary of collapse loads

5434

psi...