It can be assessed from laboratory stress tests on cores.

There is also a number of popular correlations on initial formation porosity summarized in the table below:

Corrrelation

Name/Author

Scope

c_\phi = 2.71 \cdot \phi_i^{-0.415} \cdot 10^{-7} \ \textrm{kpa}^{-1}

Hall

Consolidated sandstone under typical formation pressure

c_\phi = 1.45 \cdot \exp \big[ 4.026 - 23.07 \ \phi_i + 44.28 \ \phi_i^2   \big] \cdot 10^{-7} \ \textrm{kpa}^{-1}

Newman

Consolidated limestone,

c_\phi = 1.45 \cdot \exp \big[ 5.118 - 32.26 \ \phi_i + 63.98 \ \phi_i^2   \big] \cdot 10^{-7} \ \textrm{kpa}^{-1}

Newman

Consolidated sandstone,

c_\phi = 1.45 \cdot \exp \big[ 34.012 \cdot ( \phi_i - 0.2)  \big] \cdot 10^{-7} \ \textrm{kpa}^{-1}

Newman

Unconsolidated sandstone,

Reference