The dynamics of immiscible two-phase flow in geological fractured formations are fundamental to a wide range of subsurface processes, including the development of unconventional reservoirs such as shale and coalbed reservoirs. This study aims to explore the combined effects of wall surface roughness and wettability on immiscible displacement control within fractures and complex fractured porous media. The geometric models with rough surfaces are reconstructed to incorporate grooves with deviation depths that conform to a Gaussian distribution. The fracture networks are extracted from coal samples. The volume-of-fluid method based on Navier–Stokes equations is adopted to simulate two-phase flow. A systematic series of simulations is conducted to explore the impact of surface roughness and wall wettability on displacement dynamics. The results from single-fracture models demonstrate that higher roughness intensifies more pore-scale pinning events, resulting in unstable fingering flow and higher residual saturation. This effect is further exacerbated when combined with strong water-wet or oil-wet conditions, whereas intermediate wetting conditions mitigate fluid entrapment. Pore-scale observations reveal that this phenomenon arises from the dynamic interface reversal effect of the fluid–fluid interface under intermediate wetting conditions, which enables trapped fluids to be displaced from the grooves of rough surfaces. The interplay between surface roughness and wall wettability leads to a more complex and localized distribution of residual fluids in fracture networks. These insights contribute to a deeper understanding of pore-scale displacement dynamics in geological fractures and provide critical insights for optimizing hydraulic fracturing and displacement and surface gathering strategies in the development of unconventional reservoirs.
Yang et al. (Mon,) studied this question.