Extended DLVO-based estimates of surface force in low salinity water flooding

Abstract

Low salinity water flooding (LSWF) has been in the center of attention as a cost-effective technique to improve oil recovery in the last decade. While wettability alternation is considered as the main mechanism behind low salinity effect (LSE), the understanding what factors control the wettability variation is incomplete. Detailed understanding of the interaction of the system of Crude Oil/Brine/Rock in a molecular level is an essential step to pinpoint the mechanism(s) of wettability alternation, thus screening the potential reservoir candidates for low salinity water flooding, also guiding industry to design injected brine chemistry to maximize the oil recovery. We therefore used extended DLVO theory to model a suit of disjoining pressure on clays and Berea sandstone with two oils and aqueous ionic solutions, based on experimental data from a literature [1].We estimated the effect of cation types (NaCl, MgCl2 and CaCl2), concentrations (0.2, 1, and 5wt.%) on disjoining pressure with the presence of various clays, two different oils and Berea sandstones. We also compared the disjoining pressure results with core-flooding experiments in the literature [1]. Our results show that disjoining pressure is extremely sensitive to cation types rather than salinity level. Divalent cations (0.2wt.%, CaCl2 and MgCl2) exhibits negative disjoining pressure with oils, clays and Berea sandstone, but monovalent cations (0.2, 1wt.%) shows positive disjoining pressure, suggesting that removing divalent cations from the injected brine is essential to alter the wettability, in line with results of core-flooding experiments in the literature [1]. While we did not explicitly investigate the influence of multi-component ion exchange on low salinity effect, DLVO-based model allows us to put boundaries on injected water chemistry, and deeply understand the interaction of Crude Oil/Brine/Rock system. Further, we argue that extended DLVO theory could be applied to screen candidate reservoirs for low salinity water flooding, providing industry with a guideline to manipulate water chemistry to maximize oil recovery. We also proposed a workflow to preliminarily evaluate the potential of LSE to constrain the intrinsic uncertainty of low salinity water flooding in fields.