The Effects of Roughness and Mechanical Property of Rough Fracture Surface on Hydraulic Fracture Conductivity

Fracture surface features and proppant are the two essential factors controlling hydraulic fracture conductivity. In this work, we measured the effect of fracture surface and proppant parameters on fracture conductivity based on duplicated rough fracture surfaces. To simulate the real hydraulic fracture, large number of artificially split rock samples were collected from shale outcrops. Rough fracture surface was scanned and carving technique was utilized to duplicate rough fracture surfaces on flat rock samples. After that, unpropped and propped fracture conductivity was tested. Experimental results indicated that shale samples perpendicular to bedding exhibited higher strength and rougher fracture surface, resulting in higher unpropped fracture conductivity than samples parallel to bedding. There was not a strong positive relationship between displacement and unpropped conductivity. Partial-monolayer proppant placement could bring high conductivity under low closure stress, while multilayer proppant placement sustained enough conductivity under high closure stress. Optimal proppant parameters were changed with fracture surface roughness and closure stress. Taking initial roughness of fracture surface into account, experimental results can allow us to understand the collation of rough fracture surface and proppant, and help field engineers to make rational choices for the selection of proppant parameters in shale gas fracturing.