Co-evolution of friction and permeability in a propped fracture under constant shear and implication to induced seismicity

In this study, we explore the evolution of friction and permeability of a propped fracture using shearing-concurrent measurements of permeability during constant velocity shearing experiments. We separately examine the effects of normal stress (1 MPa, 3 MPa and 5 MPa), proppant thickness (mono-, double- and triple-layer), proppant size (40/80 mesh, 30/50 mesh and 20/40 mesh) and rock texture (Green River shale and Westerly granite) on the frictional and transport response of proppant packs confined between planar fracture surfaces. The results indicate that proppant-absent and proppant-filled fractures show different frictional strength. For fractures with proppants, we observed that (1) the frictional response is mainly controlled by the normal stress and proppant thickness, (2) permeability of the propped fracture is mainly controlled by the magnitude of the normal stress, the proppant thickness and the proppant size. Permeability of the propped fracture decreases during shearing, which is plausibly due to proppant particle crushing and related clogging. Proppants become prone to crushing if the shear loading evolves concurrently with the normal loading. Above combined conclusions suggest the use of high-concentration proppants in the field, which not only provides high hydraulic conductivity for hydro-carbon production, but also help to mitigate the risk of induced seismicity.