The Salinity Dependence of Spectral Induced Polarization Studied with an Extended Model of Membrane Polarization

In order to estimate hydraulic parameters from SIP measurements, it es essential to understand the dependence of the electrical impedance not only on structural parameters describing the pore space, but also on electrochemical properties. Here, we investigate the influence of fluid salinity on the IP parameters based on an analytical model to simulate membrane polarization. The model was originally developed for a one-dimensional pore system, where the membrane effect is postulated to be caused by varying ion mobilities in two different pore types. The model was recently extended to explicitly include finite pore radii and the properties of the electrical double layer, and the membrane effect comes out naturally as a result of varying ion concentration with distance from the pore wall. We carry out simulations to study the influence of salinity on the IP effect and compare the results with experimental observations. While our results are consistent with several trends observed in experiments, such as an increasing imaginary conductivity with fluid salinity, some features, such a decrease of the imaginary conductivity at high salinities, were not yet reproduced.