Question

In a Gulf Coast well, the speed of sound is 10,000 ft/sec at a depth of 13,500 ft. The normal speed of sound at this depth, based on extrapolated trends, would be 12,000 ft/sec. What is the pore pressure at this depth?

Answer 1

0.69 psi/ft

Step-by-step explanation:

speed of sound at depth of 13500 ft = 10000 ft/sec

normal speed of sound at 13500 ft = 12000 ft/sec

time taken to travel at 10000 ft/s (t) =
`(1)/(10000)sec`

time taken to travel at 12000 ft/s(t n) =
`(1)/(12000)sec`

assume overburden stress gradient = S/D = 1 psi/ft

normal pore pressure gradient =
`((P)/(D))_n`= 0.465 psi/ft

using imperical formula

`(P)/(D) = (S)/(D) - [(S)/(D)-((P)/(D))_n] ((\Delta t_n)/(\Delta t))^3`

=
`1 - [ 1- .465]((10000)/(12000))^3`

= 0.69 psi/ft

Pore pressure = 0.69 psi/ft