Thermal deterioration of high-temperature granite after cooling shock: multiple-identification and damage mechanism

Cooling shock has a significant thermal deterioration (TD) on the physical and mechanical properties of rocks in high-temperature conditions, which is a critical concern for the engineering application of the cyclic hydraulic fracturing technique in an enhanced geothermal system (EGS). In this work, cooling shock tests were carried out on granite samples to evaluate the actual TD of high-temperature rocks by cooling shocks, and multiple test methods were used to explore the effect of TD on the corresponding physical and mechanical properties of high-temperature granite. Some core conclusions from the study are as follows: (1) The wave velocity and apparent resistivity (AR) can reflect the thermal damage effect of cooling shocks on high-temperature granite. Notably, the higher the temperature of granite, the more significant change in wave velocity and AR. (2) The stress-strain curve tends to be smooth with the granite temperature increases and the cooling shocks intensify, the quiet period of acoustic emission (AE) events is lengthened, and the number is gradually reduced. (3) The TD effect of the cooling shock tends to be more significant for the samples at temperatures above 550 °C, and the peak stress continues to decrease with cooling shock strengthen. Furthermore, thermal stress is the main cause of TD to high-temperature granite. This study has the potential to guide the use of the cooling shock effect in extraction applications of geothermal engineering.