Effects of corner-bridge flow on capillary pressure-saturation curve in porous media

The capillary pressure curve is a fundamental constitutive relationship for simulating unsaturated flow and water-gas multiphase flow in porous media. As the wetting-phase saturation approaches the residual saturation, corner films and liquid bridges formed between solid grains become the dominant pathways governing fluid displacement processes. At present, the mechanisms by which corner films and liquid bridges influence capillary pressure curves remain insufficiently understood. In this study, a microfluidic visualization experimental platform was developed, and quasi-static drainage experiments were conducted in six sets of microfluidic models with different pore structures and surface roughness. The corner film-liquid bridge flow was directly observed, and its influence on capillary pressure curves was quantitatively evaluated. The results indicate that corner film-liquid bridge flow mainly occurs at low wetting-phase saturations and leads to a reduction in the residual wetting-phase saturation by 0.21-0.32. The occurrence of corner film-liquid bridge flow is closely related to the wettability of the porous medium; rough solid surfaces reduce the contact angle of the wetting phase, thereby facilitating the formation of corner films and liquid bridges. Moreover, the impact of corner film-liquid bridges is positively correlated with the number of liquid bridges, and their effect becomes more pronounced with decreasing porosity and heterogeneity of the porous medium.