The effect of supercritical CO₂ on failure mechanisms of hot dry rock

Hot dry rock is a clean, renewable resource of geothermal energy with good stability and a high utilization rate. Supercritical CO₂ has shown promising results for improving the permeability and heat exchange of hot dry rock. In order to demonstrate the effect of supercritical CO₂ on the failure mechanism of granite, the acoustic emission of granite during its failure process were studied in addition to X-ray diffraction, scanning electron microscopy, and optical electron microscopy investigations. The experimental results showed that for granite without supercritical CO₂ treatment, as it approached failure, there were many acoustic emission events with a waiting time less than 0.0001 s, and that the power law exponent of the acoustic emission energy distribution decreased. The failure mechanisms were a combination of fracture and friction, with fracturing dominant. After immersion in supercritical CO₂, new cracks and pores appeared in the granite due to the dissolution of minerals, but friction was also a factor evidenced in particle crumbing. Generally, the acoustic emission statistical distributions of granite before and after supercritical CO₂ soaking conformed to the seismic statistical distribution law. This study is conducive to increasing the understanding of artificial earthquakes induced by the development of hot dry rock.