Coupled effects of fracture geometry and fluid properties on two-phase flow in rough fractures

Abstract

Two-phase flow in rough fractures is governed by the coupled effects of geometric heterogeneity and fluid properties, yet the physical mechanisms linking fracture complexity with phase transport remain insufficiently understood. In this study, a fractal-based analytical model is developed to describe two-phase flow in rough fractures by incorporating fracture roughness, aperture distribution, and flow tortuosity. Analytical expressions for permeability and relative permeability are derived. Comparison with multiple independent experimental datasets demonstrates that the model accurately reproduces the nonlinear relative permeability behavior observed in fractured media. The results reveal that fracture geometry regulates fluid transport by modifying the available flow space and resistance along flow pathways. Fracture roughness and aperture heterogeneity restrict effective transport regions and enhance energy dissipation, whereas tortuous pathways increase hydraulic resistance. In two-phase flow, relative permeability is controlled by phase distribution associated with saturation and interfacial momentum transfer induced by viscosity contrast. A lower viscosity ratio strengthens interfacial shear interaction and suppresses the mobility of the nonwetting phase, resulting in a pronounced reduction in its relative permeability. These findings elucidate the coupling between fracture geometry, interfacial dynamics, and phase transport, providing new insights into multiphase flow behavior in complex confined geometries.