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?

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wagonbelleville wagonbelleville · Answer 1 · 2019-10-03T12:42:43+02:00

Answer:

0.69 psi/ft

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) =[tex]\dfrac{1}{10000}sec[/tex]

time taken to travel at 12000 ft/s(t n) =[tex]\dfrac{1}{12000}sec[/tex]

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

normal pore pressure gradient = [tex](\dfrac{P}{D})_n[/tex]= 0.465 psi/ft

using imperical formula

[tex]\dfrac{P}{D} = \dfrac{S}{D} - [\dfrac{S}{D}-(\dfrac{P}{D})_n] (\dfrac{\Delta t_n}{\Delta t})^3[/tex]

= [tex]1 - [ 1- .465](\dfrac{10000}{12000})^3[/tex]

= 0.69 psi/ft

Pore pressure = 0.69 psi/ft