Salinity and Saturation Effects on Shaly Sandstone Conductivity

Abstract

ABSTRACT Although a considerable amount of effort has been expended on the subject, the interpretation of shaly sandstone resistivities often proves problematic. Since the amount of high quality experimental data is somewhat limited, a joint research project was conducted to acquire more laboratory data and to evaluate the data in terms of new and existing theoretical models. This project consisted of two sets of experiments: conductivity measurements on fully brine saturated rock samples investigating the effect of changes in salinity and/or type of cations; resistivity index measurements at decreasing water saturation and various salinities achieved by capillary drainage. The second set of experiments will be presented in this paper. Supporting data consist of mercury porosimetry, SEM analysis, and Qv as measured by chemical titration, membrane potential and Co vs Cw intercepts. Our data on resistivity index show that commonly used shaly-sand models such as Waxman-Smits or Dual-Water have difficulty predicting saturation when clay conductivity is dominant. This can occur when clay content is high or when brine conductivity is low. Models that incorporate additional geometrical information about the conducting paths, such as the Schwartz-Sen model or the DC model of Giouse and Argaud, do a better job of predicting the experimental results.