Experimental study on flow and heat transfer characteristics of water flowing through a rock fracture induced by hydraulic fracturing for an enhanced geothermal system

•Rock fracture used in this experiment was induced by hydraulic fracturing.•The hydraulic conductivity of a fracture in granite after hydraulic fracturing were calculated.•The effects of confining pressure on the heat transfer coefficient were discussed.•The flow and heat transfer characteristics during unloading process were discussed. An experimental study was conducted to improve the understanding of the flow and heat transfer characteristics of water flowing through a fracture induced by hydraulic fracturing for geothermal energy extraction in an enhanced geothermal system. The hydraulic conductivity, average fracture aperture and heat transfer coefficient were experimentally investigated by varying injection flow rates, confining pressures under high temperature during loading and unloading processes. The results show that the fracture aperture and hydraulic conductivity were highly stress-dependent and the hydraulic aperture cannot recover completely during unloading. In addition, the effects of flow rate and confining pressure on the heat transfer coefficient were discussed. It is found that the convection heat transfer coefficient increases slightly with the increase of confining pressure during loading.