A measure of formation porosity change due to pressure
variation:
c_r = \frac{1}{\phi} \frac{\partial \phi}{\partial p} |
There is a statistical correlation between initial formation compressibility and formation porosity which can be picked by various compressibility-porosity models.
Pore compressibility stays constant for small pressure variations but in a wide range of pressure variations the dependence on ambient pressure can not be neglected and should be tabulated from laboratory core tests or estimated from compressibility-pressure correlations.
The typical values are:
c_r = 0.5 \div 1.5 \cdot 10^{-6} \, {\rm kPa}^{-1} |
but may go higher for poorly consolidated rocks.
Petroleum Industry / Upstream / Subsurface E&P Disciplines / Petrophysics / Geomechanical Rock Modelling