Simandoux (total shale) equation

Input(s)

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

$R_{t}$: Rock Resistivity (dimensionless)

$R_{w}$: 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)

$$ S_{w}=\left(0.4 * \frac{R_{w}}{\Phi_{e}^{2}}\right) *\left(-\frac{V_{s h}}{R_{s h}}+\left(\left(\frac{V_{s h}}{R_{s h}}\right)^{2}+\left(\frac{5 *\left(\Phi_{e}\right)^{2}}{R_{w} * R_{t}}\right)\right)^{0.5}\right) $$

Reference(s)

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