Predicting the electrokinetic properties of the crude oil/brine interface for enhanced oil recovery in low salinity water flooding

Abstract The low-salinity waterflooding (LSWF) technique during enhanced oil recoveryhas received increasing attention over the last decade. Several studies have attempted to understand the effects of LSWF through both experiments and modelling, but their results are inconsistent due to a lack of understanding of the crude oil/ brineand brine/rock interfaces. In this paper, the crude oil/ brineinterface was studied by developing a triple-layer surface complexation model. The carboxyl groups (–COOH) were attributed to the surface charge and electrical triple-layer development of the crude oil in LSWF. The zeta potentialsof the emulsion at various pH levels and the calcium and magnesium concentrations were measured to examine the interface. These data were then directly fitted to the simulated zeta potentialsto determine the surface site density of –COOH and the associated equilibrium constantsfor the dissociation and adsorption of calcium and magnesium. The –COOH site density was determined by fitting the pH-independent zeta potential, while the equilibrium constantvalues were estimated from the variations in the zeta potentialwith the changes in pH and the concentrations of calcium and magnesium. The determined surface complexation parameters were validated by comparing the experimental zeta potentialdata from different ionic solutions. The developed surfacecomplexation model was used along with the estimated parameters to predict the interface of crude oil in seawater, formation water, and their dilutions. The simulated zeta potentialresults agreed well with the experimental data, demonstrating that the model is applicable to understand the crude oil/ brineinterface in LSWF. Finally, the importance of the prediction of the surface and zeta potentialsin the evaluation of the interface and the estimation of electrostatic forces, and thus the wettability alteration, was discussed.