Damage mechanism and heat transfer characteristics of limestone after thermal shock cycle treatments based on geothermal development

Abstract

Since coal and petroleum resources are facing depletion, geothermal resources that can be stably mined for a long time are increasingly valued, especially hot dry rock (HDR). However, thermal shock damage of rock is an unavoidable problem in the development of HDR. The effects of thermal shock fatigue on the physical and mechanical properties and heat conduction of limestone are analyzed in this paper. The limestone is subjected to 1–5 heating and cooling cycles at 100 °C–500 °C. The L* a* b* values, P-wave velocity, thermal conductivity, and tensile strength of the treated limestone are obtained. The experimental results show that the P-wave velocity, thermal conductivity, and tensile strength of limestone decrease with an increase in the temperature for a constant number of thermal cycles. When the temperature is constant, the wave velocity, thermal conductivity, and tensile strength of the limestone decrease with an increase in the number of heating and cooling cycles. In addition, the numerical simulation indicates that the heat treatment temperature, the number of cycles, and the heat transfer time have significant effects on the internal heat transfer of the limestone. Changes in the calcite crystal structure due to fatigue after multiple thermal shocks can lead to cracks between crystals, significantly affecting the physical and mechanical properties of limestone. This study provides insights into the damage characteristics and heat transfer behavior of limestone under thermal shock fatigue, as well as theoretical support for the development of geothermal carbonate reservoirs.