Electrical impedance variation with water saturation in rock

We measured the electrical impedances of 22 sandstone samples during oil-dr iving-water tests using the two-electrode method. Experiments show that the imaginary part X of the impedance (R + iX) of rock may respond well to wat er saturation in the frequency range 100 Hz-15 MHz. We found that the maxim um -X values and their corresponding interfacial polarization frequencies a re linear with water saturation. The lower critical frequency is found to v ary with water saturation, in an unclear relationship with the characterist ic length of rock. The dissipation factor at the interfacial polarization f requency remains quite stable and may be an indicator of the pore structure of rock. We used an equivalent circuit to explain the dispersive behavior of rock. More than one interfacial polarization frequency in the impedance Argand plot is predicted and can be observed if the measurement frequency r ange is wide enough.