Exploring the influence of different cooling methods on the pore structure of gneiss using MCT-threshold segmentation method

Investigating the damage mechanism of rock micro structure after various heating-cooling treatments is crucial for evaluating the stability of an enhanced geothermal system. However, studies on the macro parameters of gneiss in cyclic heating-water cooling are scarce. This study designs a cyclic heating-water cooling test (25–700 °C). It determines the micro pore structure and related parameters (connected pores, porosity, and others) of the post-gneiss using micro-computer tomography (MCT), X-ray diffraction (XRD), and thin section petrographic analysis. In addition, a comparative test of cyclic heating-natural cooling is conducted to obtain the weakening mechanism of the pore structure of gneiss under cyclic heating-water cooling conditions. The findings indicated that the microstructure of gneisses subjected to the two cooling techniques exhibits similar evolutionary characteristics. When the temperature is between 300 and 500 °C, the parameters of gneisses will decrease slightly under natural cooling and increase slightly under water cooling. Due to rapid cooling, more microcracks and thermal damage will form within gneisses under water cooling. Water-induced weakening promotes physicochemical reactions of the internal mineral composition of the rock mass, resulting in great microstructural deterioration of the gneiss under thermal stress.