Pore-Scale Gas–Liquid Two-Phase Flow and Liquid Retention in Rough Pore Throats

CO2 injection offers multiple potential benefits in subsurface energy systems, including enhanced gas recovery, reservoir-pressure maintenance, mitigation of liquid blockage in water-bearing gas reservoirs, and geological storage. However, CO2–liquid two-phase flow in microscale pore throats is strongly affected by surface roughness, which controls interfacial migration and residual liquid retention. In this study, a CO2–liquid two-phase flow model was established by coupling the Navier–Stokes equations with the phase-field model. Two-dimensional regularly rough throats and three-dimensional randomly rough throats were constructed to investigate the effects of wettability, capillary number, and roughness parameters on interfacial evolution and liquid-film formation. The results show that rough surfaces alter near-wall flow distribution, enhance interfacial deformation, and increase flow resistance. Under liquid-wet conditions, CO2 tends to advance through the main flow region and leaves residual liquid films along the walls, whereas under gas-wet conditions, CO2 can enter rough grooves and mobilize part of the retained liquid. Increasing the capillary number promotes interfacial fingering and liquid-film formation, with the relative interfacial length showing an approximately exponential relationship with capillary number. Roughness height and width influence the critical capillary number for liquid-film formation by regulating the competition among capillary force, viscous force, and wall resistance. Three-dimensional simulations further indicate that stronger wall curvature intensifies local pore-radius variations and promotes liquid retention in wall depressions and pore-throat expansion regions. These findings provide pore-scale insights into CO2–liquid flow and liquid retention in rough pore throats.