s_w = \left[ \frac{\sqrt{\frac{1}{R_t}}}{ \frac{1}{\sqrt{R_{sh}}} + \sqrt{ \frac{\phi_e^m}{A \, R_w}}} \right]^{\, (2/n)} |
---------
\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} |
where constant is defined by formation shaliness
:
\frac{1}{A} = 1 + \Big( \frac{V_{sh}^{2-V_{sh}}}{\phi_e} \, \frac{R_w}{R_{sh}} \Big)^{1/2} |
where
| formation water saturation | ||
| effective porosity | ||
| shaliness | ||
| specific electrical resistivity from OH logs | ||
| specific electrical resistivity of formation water | ||
| specific electrical resistivity of wet shales | ||
| formation matrix cementation exponent | 1.5 ÷ 2.5, default value is 2 | |
| formation matrix water-saturation exponent | 1.5 ÷ 2.5, default value is 2 |