Modelling and simulation of miscible fingering instability in a two-phase system with gravity: Application to oil recovery enhancement

Enhanced oil recovery (EOR) processes rely heavily on understanding the complex behaviour of miscible and immiscible fingering, particularly under the influence of gravity, as fingering instability can significantly affect fluid displacement in two-phase systems. This study used COMSOL Multiphysics to investigate miscible fingering instability in a two-phase system affected by gravity, and included the gravitational effects in the computational model in order to take account of their influence on fluid flow dynamics. The dynamic interaction between miscible fluids was studied in order to clarify the mechanisms responsible for fingering instability and its effect on displacement efficiency. Moreover, the spatiotemporal evolution of species concentration and miscible fluid saturation was recorded in order to assess the displacement behaviour of the different injected fluids. The results highlight key benefits of miscible EOR, including improved sweep efficiency, reduced mobility ratio sensitivity, and enhanced displacement efficiency. Findings were consistent with previous investigations, and the simulations showed that nano-brines achieved higher oil recovery than carbonated water. Among the nano-agents tested, aluminium oxide performed most effectively, followed by silicon dioxide and magnesium oxide. Oil production is highly dependent on both the inclination angle and the dip direction, while this study concluded that gravity plays a significant role in inclined reservoirs, strongly influencing fluid flow behaviour.