(465a) Characterizing Anionic surfactant Retention on Berea Sandstone
In this study, we investigate the retention of an anionic surfactant, AOS1416, on Berea sandstone cores under different wettability states and surface redox potentials. Typically anionic surfactant adsorption on sandstone is thought to be low due to electrostatic repulsion between the surfactant and the mineral surface. We demonstrate that changing the surface wettability from water-wet to neutral-wet increases the surfactant adsorption significantly. Surfactant adsorption levels are determined by analyzing the effluent history data with a dynamic adsorption model assuming Langmuir isotherm. It is further illustrated that surfactant breakthrough in the neutral-wet core takes place in parallel with the extraction of the adsorbed crude oil components from the rock surface, as a sign of wettability alteration. We also show that, under water-wet conditions, changing the surface redox potential from an oxidized to a reduced state decreases the adsorption levels to some extent. This is attributed to the removal of ferric ions, as a potential surfactant adsorption sites, from sandstone surface during core reduction. Findings from this study suggest that laboratory surfactant adsorption tests need to be conducted with the consideration of surface wettability and redox state. This is crucial for obtaining adsorption levels that are representative of reservoir conditions.