Permeability evolution of fractured granite after exposure to different high-temperature treatments

A detailed understanding of permeability in fractured granite after exposure to high-temperature treatments under different confining pressures is critical for deep resource exploitation and underground space utilization. Along with the mechanical behaviour deterioration resulting from geologic and engineering effects, thermal stress leads to a permeability variation. In this research, uniaxial compression tests are performed on granite after exposure to a high-temperature treatment, and water flow experiments are then conducted on the fractured granite. A non-Darcy approach is used to analyse the permeability. When the temperature increases from 200 to 600 degrees C, changes in the microstructures are observed using scanning electron microscopy, new cracks generate along with the coalescence of original cracks, and the uniaxial compression strength and Young's modulus decrease rapidly. As the temperature increases, the permeability experiences three stages: decrease slowly, increase rapidly, and increase slowly. An exponential function fits the relationship between temperature and permeability well as the temperature is higher than 400 degrees C. When the confining pressure increases at a certain temperature, the decreasing rate of permeability at a higher confining pressure is smaller than that at a lower confining pressure, and it becomes more difficult for the seepage channels to close. As the confining pressure increases from 2 to 4 MPa at room temperature, the permeability decreases from 1.58 x 10-16 to 4.18 x 10-17 m2, decreasing by 73.54%. The decreasing rate is 16.39% as the confining pressure increases from 6 to 8 MPa.