Effect of Electrokinetics and Thermodynamic Equilibrium on Low-Salinity Water Flooding for Enhanced Oil Recovery in Sandstone Reservoirs

Wettability alteration (from oil-wet to mixed- or water-wet condition) is the most prominent mechanism in low-salinity water flooding (LSWF) for enhanced oil recovery (EOR) in sandstone reservoirs. Although several factors influence the wettability alteration, many efforts have been made to find the main controlling factor. In this study, the influence of interface properties of sandstone/brine and thermodynamic equilibrium of sandstone minerals were evaluated to understand the wettability alteration during LSWF. A triple-layer surface complexation model built-in PHREEQC was applied to a quartz/brine interface, and the modeling results were verified with zeta potential experimental data. This model was combined with that of kaolinite/brine to predict sandstone/brine interface properties. The measured and predicted sandstone zeta potentials were between those obtained for quartz and kaolinite in the diluted seawater. The predicted surface potential of sandstone together with that of crude oil was used in extended Derjaguin-Landau-Verwey-Overbeek theory to estimate the attractive or repulsive force. Consideration of thermodynamic equilibrium between minerals and solution significantly increased the pH and hence resulted in an increase in negative surface potential in the surface complexation. This provided a strong repulsive force between crude oil and sandstone, thus resulting in a more water-wet condition.