地下热流固耦合对EGS热开采的影响

人工热储的孔隙率及渗透率在增强型地热系统（EGS）地下热开采过程中受温度（T）、水力（H）、应力（M）的综合影响。本文建立了EGS热开采过程THM耦合的三维计算模型，并采用局部非热平衡假设处理液岩对流换热。对一理想的五口井EGS系统采热过程进行了THM模拟计算，分析了岩石温度、孔隙压力对岩石应力场的作用机理，进一步研究了应力场对EGS采热性能的影响。结果表明，开采过程中岩石应力场为热储内孔隙压力和温差综合作用的结果，由孔隙压力造成的岩石应力为压应力，仅集中于注入井附近，由岩石温度变化引起的热应力为拉应力，随着热开采区域的扩展而扩展。液?岩温差是触发工质与岩石热交换的动因，同时也是产生热应力的根本。

The Thermal-Hydraulic-Mechanical Coupling Effects on Heat Extraction of Enhanced Geothermal Systems

During heat extraction in enhanced geothermal systems (EGS), the reservoir porosity and permeability can be greatly affected by the multi-physical coupling of Thermal (T), Hydraulic (H), and Mechanical (M) actions. In the present work we develop a three-dimensional transient model coupling the subsurface THM behaviors during EGS heat extraction process. The local thermal non-equilibrium is assumed when describing the heat exchange between the rock matrix and heat transmission fluid. Case studies with respect to an imaginary quintuplet EGS reveal the involved mechanisms of inter-couplings in-between T-H-M actions, and the results indicate significant mechanical effects on EGS heat extraction performance. The stress of the rock matrix is largely influenced by the pore pressure and the temperature distributions. The stress triggered by fluid pressure is found to be compressive and confined in the very vicinity region of the injection well; the thermal stress is tensile and to some extent also concentrates around the injection well, but its distribution region expands toward the production well with the proceeding of heat extraction process. The temperature difference between rock matrix and heat transmission fluid is not only the driving force of heat extraction from heat reservoir but also significantly affects the formation of thermal stress in the reservoir.