Interfacial Electrochemistry of Oxide Surfaces in Oil Bearing Sands and Sandstones

It is shown that the detrital grains present in a consolidated sandstone formation and in unconsolidated sands behave as mixtures of oxides. Potentiometric titration results are presented for Ottawa sand and for unbaked and baked Berea sandstone samples. Generalized equations are presented for the site-binding model of J. A. Davis, R. O. James, and J. O. Leckie (J. Colloid Interface Sci.63, 480;65, 331;67, 90 (1978)). Such a model is used to estimate the adsorption equilibrium constants for the potential determining ions and the supporting electrolyte ions. Using these constants as input parameters the model equations are solved to yield the surface charge and surface potential distributions in the solution phase. A simplistic statistical mechanical model is developed to show that an independent estimation of the surface charges using the equilibrium constants determined from Davis' model yields values in good agreement with experiment. The potential applications of such a detailed electrochemical description of the sand and sandstone detrital grains are discussed.