(see Compressibility @ Wikipedia)@wikipedia

Synonym: Pore Compressibility = CPHI

A measure of formation porosity porosity 

c_r\phi = \frac{1}{\phi} \frac{\partial \phi}{\partial p}

The above correlation assumes constant  which holds true in many practical applications.

There is a statistical correlation between initial formation compressibility It stays constant for small pressure variations (

Pore compressibility stays constant for small pressure variations but in ) but for a wide range of pressure variations  variations the dependence on ambient pressure  pressure 

The typical values are: 

c_ϕ = 0.5 ÷ 1.5  GPa^-1

but may go higher for poorly consolidated rocks.

In many practical cases the pore compressibility can be considered as poorly dependent on reservoir pressure variation:

In this case porosity dependence on reservoir pressure can be simulated as:

\phi(p) = \phi_i \cdot \left[  1 + c_\phi \, (p-p_i)  + 0.5 \, c^2_\phi \, (p-p_i)^2 \right]

But in case the reservoir pressure is changing substantially one may need to account for the effect it takes on pore compressibility (see Pore compressibility @model) and then  reservoir pressure - porosity model is going to take the following form:

\phi(p) = \phi_i \cdot \exp \left[ \int_{p_i}^p c_\phi\, dp  \right]

See Also

...

Petroleum Industry / Upstream / Subsurface E&P Disciplines / Petrophysics / Geomechanical Rock Modelling

[Compressibility][ initial pore compressibility ]

[ Compressibility (rock) ]

[ Pore compressibility @model ]