Question

3. For a reservoir whose pore-wolume compressibiliy is 1Tx10 psi, and where overburden pressure and pore pressure increase by 1 psi and 0.5 psi, respectively, per foot of depth, show that the porosity decreases by 1%(00,-0.99) for every 1000 feet increase in depth.

Answer 1

3) Given: pore-volume compressibility, C_P=17×10^-6 psi^-1

Overdurden pressure and pore pressure are

P₂=0.5 psi and P₁=1 psi

Using the formula for calculating the pore ratio as:

  

φ1

2 17×10-6(05-1)=0.99 φ1

Which means the porosity is decreases by 1% for every 1000 ft increase in depth.