The Influence of Clay Conductivity on Electric Measurements of Glacial Aquifers

Abstract

The conductivities of pore water and clays are important mechanisms in the process of electric-current conduction through porous media. The clay conductivity contributes effectively to the process of electric-current conduction, particularly when the medium is saturated with fresh water. In the present study, the conductivity of clays was investigated in relation to the formation resistivity factor and specific surface area. The formation resistivity factor is an important parameter in defining variations of the formation and pore-water resistivities. The apparent and intrinsic formation resistivity factors, along with other petrophysical and hydrophysical parameters, were determined from surface electric measurements and analyses of sediments and water samples for a glacial aquifer (northern Germany). The aquifer is saturated with fresh water and composed of unconsolidated sediments that consist primarily of silts, sands, and gravels, with a majority of sands and a small amount of clays. The sediments of the aquifer and the overlying layers are characterized by a variety of grain sizes and lateral and vertical heterogeneities. The ratio of the intrinsic formation resistivity factor to the apparent formation resistivity factor is a good measure in interpreting the nature of relationships among several parameters that govern the electric-current conduction and fluid flow through porous media. Empirical equations, with coefficients of correlation ranging from 0.92 to 1.0, were obtained. Also, an equation that can be used to calculate clay resistivity from pure-water resistivity and formation resistivity factor (apparent and intrinsic) was obtained.