The Characteristics and Laws of Fracture Damage in the Long-Term Production Process of High-Temperature Geothermal Resources

Geothermal energy is an important renewable energy source, among which hot dry rocks (HDRs) are abundant and potential. The HDRs mass is dense, so the fractures become the only flow and heat transfer channel for fluids. It is of great engineering significance to reveal the fractures damage characteristics and laws in the long-term production process. Therefore, we carried out the real triaxial injection experiments and the water impact fracture experiments. The fracture damage characteristics and laws were analyzed by computed tomography scanning, sonic wave testing, scanning electron microscopy, and morphological scanning. To analyze the stress distribution and potential damage area, we established a thermo-hydro-mechanical coupling model based on experiments. The results obtained are as follows: the fracture morphology and volume increase significantly with the increase of temperature and stress difference, and the temperature effect is more obvious. The weak cementation in the original fracture is destroyed, accompanied by the germination of microcracks and the expansion of fractures along the tip. The maximum increase of fracture length and aperture can increase about 50 mm and 0.2 mm, and the maximum increase of fracture volume can reach 100 times. The variation of coarse-grained granite is more pronounced than that of fine-grained granite. More, there are intergranular fractures and transgranular fractures in fracture expansion. The simulation results strongly confirmed the experimental results. The fractures are the main potential damage areas, mainly shear damage in the early stage and tension damage in the later stage. The research results are expected to guide optimizing the scheme and enhancing the heat extraction.

Automated summary

This study investigated the fracture damage characteristics and laws of hot dry rocks (HDRs) in geothermal energy through experiments and simulations. The results showed that the morphology and volume of fractures significantly increased with temperature and stress difference. The findings provide guidance for optimizing schemes and enhancing heat extraction.