Nurmukanov

Production Casing (9 5/8” @ 10000 ft)

From the Drilling Program it can be seen that the following data is to be used for the design:

Casing Size : 9 5/8"

Setting Depth : 10000 ft

Top of 7” Liner : 9500 ft

Test Perforation Depth : 11250 ft

Pressure at Top of Perforation : 14.0 ppg

Minimum Pore Pressure above 10000 ft : 9.5 ppg

Maximum Pore Pressure above 10000 ft : 11.0 ppg

Mud weight in which the casing is to be run : 14.0 ppg

Density of Completion/Packer fluid : 8.6 ppg

Packer Depth : 11000

Expected gas gradient : 0.15 psi/ft

Design Factors : (Burst) 1.1
(Collapse) 1.0

Solution:

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 9 5/8” 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
= 14 x 0.052 x 11250
= 8190 psi
CITHP (at surface) = Pressure at Top of Perfs - pressure due to column of gas
(0.15 psi/ft)
= 8190 - 0.15 x 11250
= 6503 psi
Pressure at Top of Liner = CITHP plus hydrostatic column of packer fluid
= 6503 + (8.6 x 0.052 x 9500)
= 10751 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 = 9.5 x 0.052 x 9500
= 4693 psi
External pressure at surface = 0 psi

Summary of Burst Loads

Depth
External load
Internal load
Net load
Design Load
(Net Load x 1.1)

Surface
0
6503
6503
7153
TOL (9500 ft)
4693
10751
6058
6664