| (1) | \phi_z = \frac{\phi_e-\phi_0}{1-\phi_e+\phi_0} |
where
\phi_e | effective porosity |
\phi_0 | porosity cut-off |
The usual range is 0 \leq \phi_r \leq 0.65.
See also
Petroleum Industry / Upstream / Subsurface E&P Disciplines / Petrophysics (PP) / Volumetric Rock Model / Effective porosity