Influence of fracture surface roughness on local flow pattern: visualization using a microfluidic field experiment

Abstract

An understanding of the influence of fracture surface roughness on local flow patterns is critical for underground engineering and geological sciences. The flow pattern in a fracture is not only affected by the large-scale waviness of the fracture morphology, but also by the local small-scale roughness of the fracture surface, in particular the local flow pattern. The microfluidic field of flow in two fracture models with and without local small-scale roughness was investigated through a microscopic visualization hydraulic experiment. By quantitatively analyzing the velocity and vorticity in the two fracture models, the results indicate that the characteristics of the fracture microfluidic field are closely related to the local small-scale roughness. First, due to the effect of the local small-scale roughness, it is easier to generate and develop eddies in the original fractures that contain small-scale roughness. Meanwhile, the local small-scale roughness increases the velocity gradient in the vertical section of the fracture flow and further enhances the complexity of the fracture flow field. Moreover, although the small-scale roughness has little impact on the position of the maximum velocity, the area of eddies increases and the effective flow aperture is significantly reduced.