@wikipedia
A measure of formation porosity
change due to
pressure variation:
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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.
It stays constant for small pressure variations but for a wide range pressure variations the dependence on ambient pressure
can not be neglected and should be tabulated from experimental data or estimated from
compressibility-pressure correlations.
The typical values are in
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body | 0.5 \div 1.5 \cdot 10^{-6} \, {\rm kPa}^{-1} |
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but may go higher for poorly consolidated rocks.