Insights into mechanism of low salinity water flooding in sandstone reservoir from interfacial features of oil/brine/rock via intermolecular forces

Abstract Low salinity water flooding (LSWF) has gained wide attention due to low-cost accessibility and environmental friendly characteristics of the method. Since now a profound understanding dominantly including wettability alteration, multi ion exchange, and fines migration, for the displacing mechanisms of LSWF in sandstone reservoir, has been proposed. However, any mechanism is closely related to interfacial behavior of oil/brine/rock resulting from their individual material characteristics. This paper aims to give insights into the displacing mechanism of LSWF from understanding interfacial features of crude oil, brine, and rock in sandstone reservoir via intermolecular forces. Interfacial specifics including cation exchange, polar chemical group (—OH), charges, and water-solubility in sandstone, and polar fractions, charges, salting in effect, chemical bonding, and decreased IFT in crude oil play a vital role to determine the behavior of oil film on the surface of sandstone. Crude oil adsorbs onto the surface of sandstone by the main six intermolecular forces including Van der Waals force, hydrogen bond, electrostatic force, structural force, chemical bonding, and born repulsion. Hence, the wettability of sandstone changes into more oil wetness. Ionic effects deriving from low salinity water on the surface of oil/brine/rock are multi ion exchange, pH increased, expansion of electric double layer, increased hydration radius, fine migration, salting in effect, minerals dissolution, and decreased interfacial tension, respectively, which promote desorption of crude oil wettability to alter into more water wet. The main mechanisms for LSWF are concluded to wettability alteration, enlarged sweep efficiency, similar alkaline flooding, salting in effect, and decreased interfacial tension. All these mechanisms have a synergy to enhance oil recovery during LSWF. Finally, this review has also stated the mechanism about organic combination of LSWF and other EOR technologies (CO2, polymer, and surfactant flooding). It is believed that this paper can offer guidance to establish precisely quantitative characterization and conduct extensive application in oilfield in future.