Waxman-Smits or Dual-Water methods used to calculate Sw for shale-bearing formation require special parameters "Qv" and "m*/n*" or "m0/n0". Usually, they can be obtained by a kind of special core analysis called "multi-salinity resistivity measurement", but the analysis is rarely acquired, especially if it is an old data set.

The reason that multi-salinity measurements are required is that linear regression is used as the method for solving the equation. However, today's computing environment makes it possible to casually use a numerical solver. By using a numerical solver, non-linear expressions can be used to determine the parameters from the ordinary core resistivity measurements.

In this paper, the selection of the solver algorithm suitable for obtaining the parameters for Waxman-Smits and Dual- Water from ordinary core resistivity measurement is reported.

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