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Dr. Yi Xue is an Associate Professor at the Geotechnical Institute of Xi'an University of Technology, China. He received his BSc and PhD degrees from the State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology. In 2017, he was honored with the Excellent Doctoral Dissertation Award by the Chinese Society for Rock Mechanics and Engineering. He has published more than 100 scientific papers, with research interests covering rock seepage theory, multi-field coupling theory, intelligent rock mechanics, and geothermal resource development. He is a council member of the Shaanxi Society for Rock-Soil Mechanics and Engineering and serves on its Youth Committee. In 2021, he was selected for the Youth Talent Promotion Program of the Xi'an Association for Science and Technology. He has led several research projects funded by the National Natural Science Foundation of China, the Special Support of the China Postdoctoral Science Foundation, and the Special Support of the Shaanxi Postdoctoral Research Project.
Outline
Liquid nitrogen (LN2)-assisted fracturing has emerged as a promising technique to enhance the productivity of hot dry rock (HDR) geothermal reservoirs. To elucidate the progressive mechanical degradation and fracture mechanisms of granite under cyclic thermal shocks, this study integrates ultrasonic testing, acoustic emission (AE) monitoring, three-dimensional profilometry, and uniaxial compression testing. Damage evolution was assessed through velocity attenuation, waveform distortion, and AE characteristics, while microcrack propagation and fracture morphology were analyzed using scanning electron microscopy and surface topography reconstruction. The degradation process exhibits a distinct cycle-dependent transition, evolving from tensile microcrack initiation during early cycles to shear-dominated failure during prolonged cycling. In Phase Ⅰ (1-3 cycles), initial thermal stresses induce axial tensile microcracks, leading to sharp decreases in P-wave velocity (53.45 %) and amplitude (40.55 %). Frequency analysis reveals a narrowing and convergence of secondary bands, whereas the fracture surfaces exhibit low undulation, dominated by tensile failure. In Phase II (3-20 cycles), shear-dominated damage progressively develops, as cyclic cooling enhances crack connectivity. AE activity intensifies sharply, correlating with macroscopic shear crack networks. Fracture surfaces evolve toward step-like morphologies, with roughness parameters increasing by up to 277.43 %, indicative of composite tensile-shear failure. Cyclic LN2 cooling significantly lowers crack initiation stress and fracture energy, while promoting crack density and surface roughness. These findings provide critical insights into the mechanisms of LN2-induced fracture enhancement, highlighting its potential to optimize HDR reservoir stimulation strategies.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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