增强型地热系统（EGS）开发中耦合作用下注水压裂剪切裂纹形成机制及造缝机理研究

深入研究干热岩储层剪切裂纹形成及造缝机制，是突破干热岩增强型地热系统（EGS）开发技术瓶颈且亟需解决关键难题。课题以EGS地热开发中耦合作用下注水压裂造缝机理为研究目标，首先研发真三轴直剪试验盒，进行不同温度、液压和应力条件下真三轴直剪试验，揭示剪切裂纹动态演化特征和滑移破坏机制；其次对含预制裂纹类岩石试件进行耦合注水压裂剪切试验，得出类岩石突变失稳诱发裂纹起裂的力学和能量触发条件，分析岩石耦合环境下裂纹传播和贯通规律；再次研究干热岩储层原生裂隙空间分布特征及扩展演化规律，建立干热岩剪切裂纹发育扩展造缝机理数学模型，揭示注水压裂剪切造缝机理；最后开发完善FRACOD软件中裂隙-力-热-液（FMTH）耦合模块，建立岩体地热开采的力学模型，研究不同深度、不同力学参数和注水参数变化对岩体破坏的影响，为靶区注水井和生产井位置选择提供指导。课题对我国发展清洁可再生能源具有重要的理论价值和指导意义。

In-depth study on the formation of shear cracks and the mechanism of fracture formation in hot dry rock reservoirs is the key to overcome the technology bottleneck of the Enhanced Geothermal Systems (EGS) and needs to be addressed urgently. In order to understand the fracture initiation mechanism during hydraulic fracturing under coupled effect of EGS geothermal development, we will first develop the true triaxial direct shear box, carry out the shear test of natural rock specimens under different temperature, hydraulic pressure and stress conditions, and reveal the dynamic evolution process of shear crack. Secondly, we will carry out the coupled hydraulic injection / fracture shear test on the rock specimens with prefabricated cracks, obtain the mechanical and energy thresholds of crack initiation for sudden instability, and analyze the characteristics of crack propagation and coalescence under coupled loading. Thirdly, we will study the spatial distribution and propagation process of primary fractures in hot dry rock reservoirs, and establish the mathematical model of shear crack formation and fracture initiation in hot dry rock, and further reveal the mechanism of hydraulic fracturing and shear fracture-formation. Finally, the study will develop and improve the coupled module of Fracture-Mechanics-Thermal-Hydraulic (FMTH) in FRACOD software, establish the mechanical model of rock fracturing during hydraulic fracturing, and study the influence of depth, mechanical parameters and water injection parameters on rock mass failure, which will help locating injection wells and production wells in the target area. The project has important theoretical and practical value for the development of clean and renewable energy in China.