Macroscopic and microscopic experimental research on granite properties after high-temperature and water-cooling cycles

Abstract

During drilling, reservoir fracturing and hot dry rock development, high-temperature rock is subjected to cyclic water cooling. The mechanical properties and microscopic characteristics of granite exposed to high-temperature and water-cooling cycles were investigated experimentally. The results show that the uniaxial compressive strength and elasticity modulus decrease with increasing temperature and cycles, especially above 400 °C and after 1 cycle. In addition, the P-wave velocity decreases continuously and rapidly with temperature and it drops dramatically after 1 cycle and then more slowly with increasing cycles. The inhomogeneous expansion of minerals and cyclic thermal shock are the essential reasons for rock deterioration. The decay of elasticity modulus and enlargement of void space stops the damage to granite from being aggravated after a certain number of cycles. There is a good correlation between the P-wave velocity and mechanical parameters, and the damage factor based on the uniaxial compressive strength and elastic modulus has a positive correlation with the damage factor obtained by the ultrasonic method, illustrating that the ultrasonic method can be utilized to reflect the changes in mechanical characteristics.