Consider a fomation rock of volume equal to 150 cc with a porosity of 0.18. compressibility of this sample is 12x104 psi". You are asked to calculate the percent change in the pore volume and to calculate the new porosity if the fluid pressure in the rock is reduced from 10000 psia to 1000 psia. The formation For your calculations a. use the approximate compressibility equation for small er values b. use exact compressibility equation