Pore-doublet computational fluid dynamic simulation of the effects of dynamic contact angle and interfacial tension alterations on the displacement mechanisms of oil by low salinity water

Abstract

Using our recently developed model, for the first time in the literature, the effect of fluid/fluid and rock/fluid interactions on the performance of Low Salinity Waterflooding (LSWF, as an Enhanced Oil Recovery process) at pore-doublet scale is investigated. The model is incorporated into OpenFOAM and both the Navier-Stokes equation for oil/water two-phase flow and the advection-diffusion equation for ion transport (at both fluid/fluid and rock/fluid interface) are solved via direct numerical simulation (DNS).The model is validated against imbibition and drainage pore-doublet experiments reported in the literature, and then applied to investigate the sole effect of wettability alteration as well as its coupled effect with interfacial tension (IFT) variations on the redistribution and transport of phases within the model. Different degrees of contact angle alteration, different trends of IFT variations reported in the literature, as well as different injection scenarios (secondary or tertiary) are considered.Simulation results show that in the case of high salinity water flooding (HSWF), IFT (within the range of 30 to 5 mN.m−1) has very limited effect on the residual oil saturation of the investigated model. For the case of HSWF in the oil-wet pore-doublet model (contact angle = 140°), significant amount of oil will be trapped in the small pores of the model. This residual oil cannot be produced in the absence of wettability alteration, no matter how much the IFT be reduced during LSWF (even as low as 0.1 mN.m−1). However in the absence of any IFT variation (IFT = 10 mN.m−1), the residual oil ganglia can be displaced with the sufficient degree of wettability alteration (contact angles below or equal to 30°). Nevertheless, in the presence of adequate contact angle reduction, fluid/fluid interactions (different IFT variation) can affect the outcome of the enhanced oil recovery. The LSWF performance boosts under appropriate degree of fluid/fluid and rock/fluid interactions as it leads to the coalescence of the detached or partially detached residual oil blobs and progress of chasing water front in both small and large pores of the doublets towards the downstream of the model. The results confirm the importance of fluid/fluid interactions such as IFT variation on such coalescence and dynamic LSWF, especially in the case of secondary LSWF.