Influence of electrical surface charges on thermodynamics of wettability during low salinity water flooding on limestone reservoirs

Abstract

Wettability is an important factor in controlling the displacement efficiency and ultimate oil recovery in oil-wet naturally fractured reservoirs. The scope of this study extends from the experimental investigation to analytical approach based on the DLVO theory to thin film stability evaluation. The zeta potentials on limestone rock/brine and oil/brine interfaces, and also, the electrical double layer, the London–van der Waals, and the structural forces are measured to model the disjoining pressure isotherms with the brine solutions containing monovalent and divalent ions. Then, the stability of the wetting film on the limestone surface is compared with IFT measurements, contact angle and core flooding experiments. Based on results, strong negative charges at rock/brine and oil/brine interfaces were occurred during sea water injection and increase the repulsive forces at the rock/oil interface to release the oil film from the limestone surface. Also, the oil recovery in case of Na+ in the presence of SO42− is 50% higher than it for both cases of Na+/K+ and Cl−. From the disjoining pressure isotherms, a more stable water film observes from the low salinity brine containing the Mg2+ in the presence of Cl− compared to Mg2+ in the presence of SO42−.