An Experimental Study on Seepage within Shale Fractures due to Confining Pressure and Temperature

Seepage of groundwater within rock fractures is widespread. The seepage conditions in the fractures can be affected by the stress and temperature conditions. Shale seepage conditions are a complicated coupling of stress and temperature. Experiments were carried out on shale samples containing three types of fractures: a single short fracture (type A), a single long fracture (type B), and symmetrical short fractures (type C). Three temperature conditions were set for type A. The coefficient C , which is defined as the ratio between the seepage pressure and the flow rate, is constant when the temperature effects are slight. Linear correlations between the coefficient C and the temperature were simulated. For type B, four confining pressures were applied using the confining pressure pump. As the confining pressure increases, the seepage pressure increases. The seepage pressure distribution is nonlinear when the flow rate increases to 6 ml/min under a confining pressure of 12 MPa. For type C, three temperature conditions with three confining pressure conditions were analyzed to determine the seepage pressure. The effects of the confining pressure on the seepage pressure are different from those of type B. Nonlinear curves occur under confining pressures of 3 MPa and 6 MPa at 50°C. The seepage pressure values at 70°C are smaller than those at 30°C and 50°C. The coefficient C contour is depicted for the experimental ranges of temperature and confining pressures. The small value region of coefficient C occurs at about 6 MPa and 50°C. The nonlinear increase in the seepage pressure in the fractures occurred when the confining pressure was larger for a single fracture and when the confining pressure was lower for double fractures.