Crack propagation in high-temperature granite after cooling shock: experiment and numerical simulation.

Achieving crack propagation and rapid deterioration of high-temperature rock masses by using cooling shocks is important for improving the efficiency of low-permeability oil and gas production, geothermal well pumping, and other engineering facilities. In this study, the temperatures of four groups of granite samples with holes were set as 150, 350, 550, and 750 °C. To study the crack propagation in high-temperature granite suffering from different cooling shocks, the cooling shock temperatures were set as −20, 0, 20, and 25 °C in experiments and an RFPA2D-Thermal numerical simulation. The results indicated that in the range of 350–550 °C, there is a critical temperature for the sudden change of the crack macroscopic shape. Numerous open cracks appeared on the rock surface, and the thermal damage caused by the cooling shocks was significantly enhanced within the temperature range. Additionally, under the action of the cooling shocks, cracks were initiated in the high-temperature granite at the boundary of the cooling shock hole and the sample and extended radially to the interior of the sample. Moreover, in the process of crack propagation, there was always an annular heat-balance zone inside the rock. Thus, the cracks generated at the boundary of the cube are not connected to the cracks formed at the center hole. A larger temperature gradient in the rock led to a higher crack propagation rate, larger penetration depth, and higher density of cooling-induced cracks. The results of this study can not only improve the permeability of reservoir rocks but also have important reference value for rock engineering in high-temperature environments. [ABSTRACT FROM AUTHOR]