Analytical Study of Permeability Properties of Loose Sandstone Based on Thermal-Hydraulic-Mechanical (THM) Coupling

Abstract

The permeability of reservoirs is a key factor affecting the exploitation and utilization of geothermal resources. This test used a core flow meter and other advanced experimental devices to investigate the evolution of the permeability characteristics of loose sandstone samples (with a diameter of 25 mm and a length of 50 mm) in the Zijiao Town area under various temperatures, confining pressures, injection rates, and cyclic loading and unloading conditions. The results show that (1) as the temperature increases, the overall trend of rock permeability decreases, which is mainly related to the thermal expansion of rock particles. In addition, the higher the temperature, the greater the gravel outflow. (2) The critical pressure for pore closure in the unconsolidated sandstone in the region is approximately 15 MPa. (3) The permeability change of loose sandstone under low injection rate conditions is relatively small and can be neglected. However, there is reason to believe that under high-flow injection conditions, the permeability of this type of rock mass will undergo significant changes. (4) Under the condition of loading and unloading, the permeability ratio curve of the unloading stage at three temperatures is almost a straight line. The higher the temperature, the smaller the slope, and the permeability at 20 °C with the highest recovery degree is only about 50% of the initial one.