Corner-driven mobilization of trapped oil in a square microchannel: Synergistic roles of corner water channels and water film

This study employs three-dimensional numerical simulations based on the Volume of Fluid (VOF) method to investigate the migration mechanism of a discontinuous oil phase during water flooding in square cross-section microchannels. The effects of critical parameters—capillary number, contact angle, interfacial tension, oil saturation, and viscosity—on the pressure drop, velocity, and solid–oil contact area are systematically analyzed. The results demonstrate that the migration process can be divided into four distinct stages: static stage, contact line development stage, wall detachment stage, and stable flow stage. The formation and evolution of corner water channels of the microchannel are identified as the key factor driving droplet detachment from the wall and significantly reducing flow resistance. Under high capillary numbers and low contact angles, corner water channels form and connect more readily, serving as the primary driving force for droplet detachment. Low interfacial tension or high viscosity tends to induce droplet breakup, which compromises the stability of the corner water channels. At high oil saturations, the lubricating effect of the water film is enhanced. Collectively, these parameters govern the detachment process and the evolution of flow resistance by modulating the synergistic interaction between the corner water channels and the water film. The study clarifies the synergistic role of corner water channels in promoting oil phase detachment and migration, providing a theoretical foundation for understanding pore-scale residual oil mobilization and optimizing water-flooding strategies to enhance oil recovery.