Experimental Study on the Effect of Temperature and Cooling Method on the Mechanical Properties of Granite

During the drilling process in hot dry rock formations, the action of drilling fluid may lead to the cooling effect on the rocks at different temperatures in the bottom hole, causing the changes in the mechanical properties and failure modes of rocks. To investigate the effects of temperature and cooling method on the mechanical properties of hot dry rock, granite was used instead of hot dry rock to conduct acoustic and compressive mechanical experiments on rock samples after natural cooling and water cooling at different heated temperatures, ranging from 100 ℃ to 800 ℃. The influence of temperature and cooling method on the mechanical parameters of rock were studied such as acoustic wave velocity, compressive strength, elastic modulus, Poisson's ratio and so on. Also, the macroscopic failure mechanism of rock under different treatment methods was analyzed. The experimental results indicate that the mechanical parameters of granite gradually decrease when the temperature exceeds the critical threshold, with the most significant decrease by 23% occurring at 400 ℃. The increase in temperature causes granite to exhibit ductile failure characteristics, resulting in a decrease in uniaxial compressive strength. The compressive strength of granite decreases more significantly from 400 ℃ to 700 ℃. The strength of granite decreases by about 13% after being cooled by water compared to natural cooling. The study could provide reference for the influence of drilling fluid cooling effect on rock mechanics and the calculation and analysis of formation parameters by acoustic logging in the process of hot dry rock drilling.