Wettability Alteration during Low-Salinity Waterflooding and the Relevance of Divalent Ions in This Process

Abstract

From laboratory and field test results, it is now largely agreed that reducing the overall salinity, especially the concentration of divalent ions of the injected water, can markedly improve the oil recovery. However, as a result of the complexity of the crude oil–brine–rock (COBR) system, there is no clear explanation of why the divalent cations (Ca2+) are of major significance in a low-salinity water effect (LSWE). In the present paper, spontaneous imbibition, ζ-potential measurements, static adsorption/desorption of benzoic acid (BA) onto crushed Berea, and BA self-assembled layers on silica wafer have been performed to correlate macroscopic wettability alteration during low-saline water flood with the microscopic release of the hydrophobic layers (organic acid layers) on mineral surfaces and explain the relevance of active cations (Ca2+) in this process, thereby providing a better understanding of the underlying mechanisms of a LSWE. Spontaneous imbibition results show that initial wettability of the ...