ENERGY EVOLUTION MECHANISMS IN GRANITE DEFORMATION AND FAILURE UNDER HIGH-TEMPERATURE AND HIGH-PRESSURE TRUE TRIAXIAL LOADING CONDITIONS

The deep buried hill reservoirs in the Bohai Basin, with burial depths exceeding 4000 m, represent significant targets for exploration and development. However, their exploitation is challenged by extreme geological conditions: formation temperatures can reach 200 ℃, and in-situ stresses range from 90 to 120 MPa. Under such high-temperature and high-pressure environments, the deformation and failure behavior of reservoir rocks differ substantially from that observed at shallower depths. In particular, the energy evolution mechanisms governing rock deformation and failure under true triaxial stress and high-temperature coupling remain inadequately understood. To address this issue, this study employed a self-developed true triaxial testing system capable of simulating deep reservoir conditions (maximum temperature: 200 ℃; maximum confining pressure: 200 MPa) to systematically investigate the effects of temperature and stress on the mechanical properties and energy evolution of granite. Tai-2 gray-black granodiorite was selected as a representative reservoir rock analog. Stress-strain curves were obtained under high-temperature and high-pressure conditions simulating depths of up to 5700 m. Post-experiment samples were scanned using high-energy accelerator CT, with a focus on analyzing energy evolution throughout the rock deformation and failure process. The results indicate that at relatively low stress levels, increasing temperature significantly raises both the input energy and dissipated energy required for rock failure, enhancing ductile behavior. In contrast, under high in-situ stress conditions, elevated temperature reduces the energy required for rock fracture, promoting brittle failure. The total energy required for rock failure increases approximately linearly with rising principal stress levels, exhibiting a notable brittle-ductile transition. Furthermore, increasing the intermediate principal stress enhances rock brittleness, but its effect on energy consumption is depth-dependent: at 4000 m depth, a higher intermediate principal stress slightly increases both input and dissipated energies; however, at 5700 m depth, increasing the intermediate principal stress leads to a decrease in both input and dissipated energies. This study elucidates the complex coupled effects of temperature, stress, and intermediate principal stress on deformation characteristics and energy evolution, providing crucial experimental data and theoretical support for the safe and efficient drilling and development of deep buried hill reservoirs in the Bohai Basin.