Abstract: To compare the differences in flow and heat transfer properties between tensile and shear fractures, this study used a custom-built flow and heat transfer testing device to conduct flow and heat transfer experiments on granite samples containing either a single tensile fracture or a single shear fracture. The experiments were respectively performed under constant temperatures of 50, 100, 150, and 200  ℃, while the confining pressure in each test was gradually increased from 5 MPa to 20 MPa. The results show that, in terms of flow properties, both the hydraulic aperture and permeability of the tensile and shear fractures decrease with increasing confining pressure. However, the hydraulic aperture and permeability of shear fractures are higher than those of tensile fractures, with the hydraulic aperture being approximately 20%-24% higher and the permeability about 44%-56% higher. In terms of heat transfer, both the heat extraction rate and overall heat transfer coefficient decrease with increasing confining pressure, but shear fractures exhibit higher values at all tested temperatures. Specifically, the heat extraction rate and heat transfer coefficient of shear fractures are about 140% higher at 50  ℃ and about 80%-84% higher in the range of 100-200  ℃. These results demonstrate that shear fractures show better flow and heat transfer properties than tensile fractures. These findings on the flow and heat transfer properties of tensile and shear fractures under different temperature and confining pressure conditions are of great importance for understanding fluid flow and heat transfer behavior in real enhanced geothermal reservoirs.

Key words: geothermal energy, high temperature granite, tensile fracture, shear fracture, flow and heat transfer