Exercise 1 Pore Pressure Profiles
a. The following pore pressure information has been supplied for the well you are about to drill. Plot the following pore pressure/depth information on a P-Z diagram :
|
DEPTH BELOW |
|
|
DRILLFLOOR |
PRESSURE |
|
(ft) |
(psi) |
|
0 |
0 |
|
1000 |
465 |
|
5000 |
2325 |
|
8000 |
3720 |
|
8500 |
6800 |
|
9000 |
6850 |
|
9500 |
6900 |
b. Calculate the pore pressure gradients in the formations from surface; to 8000ft; to 8500ft; and to 9500ft. Plot the overburden gradient (1 psi/ft) on the above plot. Determine the mudweight required to drill the hole section: down to 8000ft; down to 8500ft; and down to 9500ft.
Assume that 200 psi overbalance on the formation pore pressure is required.
c. If the mudweight used to drill down to 8000ft were used to drill into the formation pressures at 8500ft what would be the over/underbalance on the formation pore pressure at this depth?
d. Assuming that the correct mudweight is used for drilling at 8500ft but that the fluid level in the annulus dropped to 500 ft below drillfloor, due to inadequate hole fill up during tripping. What would be the effect on bottom hole pressure at 8500ft?
e. What type of fluid is contained in the formations below 8500ft.