Fertl and Hammack equation

Input(s)

F: Formation Resistivity Factor (dimensionless)

$\Phi_{e}$: Effective Porosity (fraction)

$R_{t}$: Rock Resistivity (ohm m)

$R_{w}$: Formation Water Resistivity (ohm m)

$V_{s h}$: Bulk Volume Fraction of Shale (fraction)

$R_{s h}$: Shale Resistivity (ohm m)

Output(s)

$S_{w}$: Water Saturation (fraction)

Formula(s)

$$ S_{w}=\left(\frac{F * R_{w}}{R_{t}}\right)^{0.5}-\frac{V_{s h} * R_{w}}{0.4 * \Phi_{e} *\left(R_{s h}\right)} $$

Reference(s)

Bassiouni, Z., 1994, Theory, Measurement, and Interpretation of Well Logs. SPE Textbook Series Vol. 4. Chapter 1, Page: 16.