(1)	$\begin{array}{l}\displaystyle s_w = \left[ \frac{\sqrt{\frac{1}{R_t}}}{ 1 + \sqrt{ \frac{\phi_e^m}{A \, R_w}}} \right]^{\, (2/n)}\end{array}$

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(2)	$\begin{array}{l}\displaystyle \frac{1}{R_t} = \frac{\phi_e^m \, s_w^n }{A R_w} \quad \Rightarrow \quad s_w = \Big ( \frac{A}{\phi_e^m} \; \frac{R_w}{R_t} \Big) ^{1/n}\end{array}$

where constant $\begin{array}{l}A\end{array}$ is defined by formation shaliness $\begin{array}{l}V_{sh}\end{array}$ :

$\begin{array}{l}\displaystyle \frac{1}{A} = 1 + \Big( \frac{V_{sh}^{2-V_{sh}}}{\phi_e} \, \frac{R_w}{R_{sh}} \Big)^{1/2}\end{array}$

where

$\begin{array}{l}s_w\end{array}$	formation water saturation
$\begin{array}{l}\phi_e\end{array}$	effective porosity
$\begin{array}{l}V_{sh}\end{array}$	shaliness
$\begin{array}{l}R_t\end{array}$	specific electrical resistivity from OH logs
$\begin{array}{l}R_w\end{array}$	specific electrical resistivity of formation water
$\begin{array}{l}R_{sh}\end{array}$	specific electrical resistivity of wet shales
$\begin{array}{l}m\end{array}$	formation matrix cementation exponent	1.5 ÷ 2.5, default value is 2
$\begin{array}{l}n\end{array}$	formation matrix water-saturation exponent	1.5 ÷ 2.5, default value is 2

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