Pore-scale investigation of immiscible displacement in rough fractures

Immiscible displacement in geological fractures is crucial for various subsurface processes. This paper aims to study the microscopic interaction between fluid and complex rough wall, and how roughness controls the immiscible displacement in fractures. The geometry model of rough surfaces is reconstructed embodying grooves with deviation depths following a Gaussian distribution. The immiscible flow and interface morphology are simulated by the Navier-Stokes equation coupled with a phase-field method. The effects of surface roughness, wall wettability and capillary number on immiscible displacement are systematically investigated through a series of displacement simulations. The results show that the pinning behavior of contact line appears at the rough surface, impelling the growth of interface length and finger formation. The surface roughness contributes to strengthening the wettability effect on interface deformation. The increasing surface roughness promotes the occurrence of contact line jumping, which causes fluid trapping in the grooves of rough surface. The amount of trapped fluid increases with capillary number in rough fractures and the critical capillary number of finger formation decreases with the increase of rough degree. The presented results can significantly improve our fundamental understanding on microscopic displacement process in geological fractures and assist to optimize the displacement scheme for enhanced oil recovery.