3D Pore-Scale Study of Dynamic Interfacial Interactions Effects in Natural Porous Rocks with Various Pore Structures

Summary Dynamic fluid-fluid and fluid-rock interactions commonly take place during subsurface reservoir exploitation, such as low-salinity waterflooding (LSWF) and carbon dioxide (CO2) enhanced oil recovery (EOR). A fundamental understanding of the two-phase flow behavior under conditions of dynamic interfacial interactions is essential to address these engineering issues. However, the multiphase flow with dynamic interfacial properties in different 3D realistic porous media remains insufficiently understood. For this study, we used a pore-scale LSWF model that integrates wettability alteration kinetics and dynamic interfacial tension (IFT) change to perform direct numerical simulations (DNSs) through the reconstructed digital rock model of sandstones. The sole impact of wettability alteration, IFT reduction, and their coupled influence on interfacial dynamics and displacement efficiency during tertiary LSWF is investigated, while pore structure measurements are incorporated to analyze their correlations with residual fluid saturation. Simulation results demonstrate that pore structure heterogeneity significantly influences trapped fluid redistribution and saturation. A lower wettability alteration degree is adequate for low-salinity water (LSW) to invade the vast majority of pores in samples with high porosity and large pore throat size. Increasing the wettability alteration degree promotes rich pore-filling dynamics, enabling LSW to penetrate more oil-saturated small pores. Concurrently, oil backflow and corner film flow become dominant, while pore systems with narrow throats and poor connectivity experience frequent fluid reentrapment events, resulting in a lower oil recovery factor. The residual oil saturation exhibits a positive correlation with tortuosity but only a weak linear correlation with aspect ratio. The high coordination number, reflecting global connectivity, effectively suppresses the negative effects of high aspect ratio under strong wettability alteration, reducing the residual trapping of nonwetting fluid. The IFT reduction enlarges the LSW swept region by decreasing the capillary resistance of narrow pores, which has a synergistic effect with low wettability alteration degree. However, this synergy progressively diminishes as the degree of alteration increases, due to weakened corner flow in swept pores. There exists an optimal combination between the IFT reduction and the wettability alteration degree that can optimize the benefits of LSWF.