Estimation of permeability from well logs using resistivity and saturation data

The interpretation of brine saturation, S_w, and corresponding rock resistivity, R_t, can determine the permeability of the rock. To eliminate the brine resistivity effect, an apparent formation factor, F_a, would represent the rock resistivity. F_a represents the ratio of the partially saturated rock resistivity, R_t, to the brine resistivity, R_w. It was observed that the apparent formation factor versus water saturation curves for samples of different permeabilities behaved similarly to capillary pressure curves where each permeability is represented by a unique curve. Therefore, permeability becomes a function of F_a and S_w. When fractional brine saturation reaches 1.0, permeability becomes a function of F_a only.