Experimental Research on the Permeability of Granite Under Different Temperature Cycles

In this paper, through the permeability test of granite under different temperature cycles, the change law of porosity and permeability of rock samples after different temperature cycles was studied, and the relationship between the P-wave velocity and porosity and permeability was established by regression analysis. The results show that the porosity and permeability of the granite samples decreased significantly in one to three high-temperature cycles, showing a logarithmic change, and with the increase of the number of cycles, the decreasing rate gradually decreased after five to 10 thermal cycles, which is beneficial to the long-term development of deep geothermal resources. Under thermal cycles at different temperatures, the P-wave velocity of granite has a logarithmic correlation with permeability and porosity. As the number of cycles increases, the relationship between permeability, porosity, and P-wave velocity changes from a logarithmic relationship between one to three cycles to a linear relationship between five to 10 cycles. After thermal cycle treatment at different temperatures, there is an excellent logarithmic relationship between the P-wave velocity and porosity and permeability, and it has a high correlation. The porosity and permeability of granite can be estimated nondestructively by measuring the wave velocity. Using a scanning electron microscope (SEM) to observe the granite at 450℃, trivial particles appeared between the pore structure, and the internal structure of the rock sample was destroyed under the action of the thermal cycle. The change mechanism of physical property deterioration in deep geothermal energy mining is revealed, guiding deep geothermal energy mining.