Mechanism of Vortex Disturbance Generated by Microbubbles Affecting Residual Oil: Microscopic Visual Experiments and Numerical Simulations

The water–gas dispersion system, in which gas is stabilized as microsized bubbles within a liquid phase, constitutes a stable two-phase system with a uniform spatial distribution. This method has proven effective for enhancing oil recovery in low-permeability reservoirs, demonstrating notable success in field trials. This study investigated the pore-scale mechanism of microbubble-induced vortex dynamics on residual oil mobilization through integrated microscopic visualization experiments and numerical simulations. Key findings reveal three critical phenomena: (1) Microbubble coalescence generates microscale vortices at merged interfaces through surface energy release; (2) these vortices enhance multiphase transport via three coupled mechanisms, intensifying interfacial energy–momentum transfer to modify oil film flow regimes, amplifying shear stress for oil film detachment, and accelerating mass transfer to reduce crude oil viscosity through oil–water–gas mixing; (3) dynamic pressure fluctuations associated with vortex formation–dissipation cycles exhibit a maximum pressure differential of 29.56 kPa, synergistically mobilizing residual oil trapped in isobaric pore throats and blind-end structures—the primary reservoirs of post waterflood residual oil. The interaction between microscale vortices and pore-scale turbulence promotes mutual amplification, increasing the pressure fluctuation intensity while increasing the fluid sweep efficiency. These insights establish a theoretical foundation for optimizing microbubble systems through controlled vortex dynamics, offering strategic implications for improving capillary-trapped oil recovery in complex porous media.