Complex conductivity of diatomites and chalks

We investigated the underlying mechanisms governing electrolytic current transmission within porous media, focusing on understanding the relationship between interface processes and the resulting complex conductivity signals. Leveraging insights from interface science literature, we aimed to clarify how adsorbed hydrated ions shape surface conduction. To achieve this, we conducted experiments of ionic adsorption on diatomite powders alongside complex conductivity of twenty-six saltwater-saturated diatomite and chalk samples. Our findings highlight a significant shift in current transmission, progressing from bound-water-dominated or slightly bulk-water-dominated conduction to solely bulk-water-dominated conduction with increasing NaCl concentration. At high salinity, ions in the adsorbed ion-water layer solidify, rendering bound-water conduction insignificant. As a result, a universal relationship emerges between sample surface area and Archie’s porosity exponent that allows for the estimation of bulk and bound water volumes from the porosity exponent. Based on these findings, a parallel conduction model using Archie’s equation was proposed as an upgrade to the dual-water model to predict sample conductivity across varying bulk water conductivity. Furthermore, our results show that chargeability peaks when the bound water-driven current transmission is significant but decreases with increasing pore water salinity due to surface ion dehydration and a shift in current transmission towards bulk water. Although the phase shift magnitude varies with pore water salinity, the frequency distribution pattern remains unchanged, reflecting the mineralogical composition of each sample. Additionally, normalized chargeability correlates with the non-conductive porosity fraction and specific surface area per pore volume. These findings hold significant implications for the petrophysical analysis of fine-grained rocks, including permeability modeling.