Impact of Wettability Alteration on the Front Instability of Immiscible Displacement in Porous Media

Wettability alteration that occurs as a result of changing the brine composition or using chemicals that lower the interfacial tension can significantly alter the mobility of nonaqueous liquid (NAPL)/water phases. Here, we show that including dynamic wettability alternation (moving from non-water-wet to water-wet) or interpolating between two sets of relative permeability curves may create an unstable displacement of the residence-fluid by the injected fluid. The instability occurs due to not only the viscosity ratio but also the new shape of relative permeability curves and their end-point values. We perform a full factorial design on Corey relative permeability parameters to determine the most destabilizing factors when the viscosity ratio is one. The observations indicate that instability proliferates when the end-point relative permeability to the NAPL phase of modified salinity brine increases, and their corresponding exponents decrease compared with high salinity brine (seawater or formation water). Besides, numerical simulations of such a displacement demonstrate that modified salinity water's breakthrough is accelerated by wettability change towards water-wet compared with a non-fingering analytical solution. This may result in a delayed mobilization of the NAPL phase in porous media. We also discuss the role of capillary pressure, heterogeneity, and secondary and tertiary injection of modified salinity water in stabilizing the shock front.