Pore geometry of Permo-Triassic sandstone from measurements of electrical spectroscopy

Abstract

AbstractIn order to provide an indirect method of estimating the hydraulic properties of sandstone aquifer rocks, electrical spectroscopy measurements were made on Permo-Triassic Sandstone over the frequency range 0.0001–1000 Hz. Samples from several boreholes across Britain are shown to exhibit a phenomenon called electrical relaxation, which we have modelled using a generalized Cole-Cole equation. The Cole-Cole parameters correlate well with other hydrogeologically important parameters determined using mercury injection capillary pressure and nitrogen adsorption techniques. Of greatest importance is that the relaxation time, τ, is strongly related to the dominant pore-throat size from which intergranular permeability may be estimated. A normalized version of the chargeability appears to be related to the surface conductivity and this gives the possibility of estimating the pore surface area to volume ratio, a value that is important in determining both permeability and sorption. The potential uses of electrical spectroscopy in hydrogeology and many other fields, including geology and petroleum petrophysics, are only now becoming apparent, and further advances are certain.