Effect of the Temperature on Nonlinear Behaviors within a single Sandstone Fracture under various normal stresses

In deep underground environments, rock fractures are subjected to combined hydro-mechanical and thermal effects from rising temperatures. This makes the internal fluid flow behavior more complex. It is crucial to comprehensively consider these coupled effects. For this purpose, a series of flow tests were conducted on artificially fractured sandstone samples. The tests were performed under various normal stresses (1-10 MPa) and temperatures ranging from 25 to 70°C. The experimental results show that flow behavior within sandstone fractures is closely related to thermal effects. Increased temperature enhances both the volumetric flow rate and the transmissivity of the fractures. Forchheimer's law remains effective in describing the nonlinear flow behavior of water under thermal effects. Higher temperatures lead to more pronounced nonlinear effects, indicating stronger inertial forces. These temperature-related phenomena may originate from two mechanisms. First, reduced water viscosity decreases flow resistance. Second, thermally induced fracture closure occurs in the rock. Within the temperature range of this study, the influence of the first mechanism on flow behavior is significantly greater than that of the second. These findings will help deepen the understanding of water flow behavior in deep underground fracture networks. They also provide practical guidance for relevant engineering practices.