title: Low-frequency complex conductivity of sandy and clayey materials.
abstract: Low-frequency polarization of sands and sandstones seems to be dominated by the polarization of the Stern layer, the inner part of the electrical double layer coating the surface of the silica grains and clay particles. We investigate a simple model of Stern layer polarization combined with a simple complexation model of the surface of the grains immersed in a 1:1 electrolyte like NaCl. In isothermal conditions, the resulting model can be used to predict the complex conductivity of clayey materials as a function of the porosity, the cation exchange capacity of the clay fraction (alternatively the specific surface area of the material), and the salinity of the pore water. A new set of experimental data is presented. This dataset comprises low-frequency (1 mHz-45 kHz) complex conductivity measurements of saprolites and sandstones that are well characterized in terms of their petrophysical properties (porosity, permeability, specific surface area or CEC, and pore size). This dataset, together with incorporating additional data from the literature, is used to test the Stern layer polarization model. We find an excellent agreement between the predictions of this model and this experimental dataset indicating that the new model can be used to predict the complex conductivity of natural clayey materials and clay-free silica sands.
authors.affiliation: Colorado School of Mines, Department of Geophysics, Golden, CO 80401, USA. arevil@mines.edu
authors.forename: A
authors.initials: A
authors.lastname: Revil
authors.forename: J D
authors.initials: JD
authors.lastname: Eppehimer
authors.forename: M
authors.initials: M
authors.lastname: Skold
authors.forename: M
authors.initials: M
authors.lastname: Karaoulis
authors.forename: L
authors.initials: L
authors.lastname: Godinez
authors.forename: M
authors.initials: M
authors.lastname: Prasad