基于管道网络模型的干热岩多场耦合地热开采机理研究

The research of mechanism of multi-physical coupling in the process of geothermal exploitation in Hot Dry Rocks (HDRs) is important for our country to ensure energy supply and to solve environmental problems. It is also a cutting-edge research area among the international community of rock mechanics, which involves several key scientific problems, such as the coupling mechanism of temperature fields and seepage fields of DHRs, the characteristics of multi-phase fluid, the chemical corrosion and crystallization etc. Most of current research is based on continuum models or simplified fracture models, which cannot reflect the complex discontinuities of HDRs and has limited our understanding of the mechanism in heat exploitation. Therefore, this research program will conduct studies based on principles of discontinuum mechanics, seepage mechanics, thermodynamics and chemistry. With the multi-phase fluid flow in fractured rocks as a main thread to string together other processes, and by applying a pipe network method that is developed for fractured rocks to build discontinuously and multi-physically coupled models, this project conducts theoretical studies of the multi-phase fluid flow in complexly fractured networks of HDRs with supercritical CO2 as working fluid; elucidates the interaction between permeability and its temperature variation; reveals the coupling mechanism between multi-phase fluid flow and deformation of HDRs; obtains the patterns of temporal and spatial evolution of permeability and thermal exploitation ratio with the consideration of the effects of chemical corrosion and crystallization; develops a numerical simulation code, which is capable of doing THMC coupled analyses in hot and complexly fractured HDRs; and finally proposes optimized design scheme and operational parameters for efficient geothermal exploitation in HDRs by using supercritical CO2 as working fluid and provides theoretical and technical supports for the geothermal energy exploitation in the future.

干热岩地热开采机理研究是国家保障能源供给，解决环境问题的重要课题，也是国际岩石力学的研究前沿，涉及高温裂隙岩体的多场耦合机理、多相渗流特性、溶蚀与结晶反应等关键科学问题。目前的研究多基于连续介质模型或简化裂隙模型，无法反映干热岩的复杂不连续性，限制了对开采机理的认识。据此，本项目以不连续介质力学、渗流力学、热力学、化学原理为基础，以多相渗流为主线，采用为裂隙岩体开发的管道网络方法建立不连续的多场耦合模型，开展以超临界CO2为工作液的干热岩复杂裂隙系统多相渗流特性的理论研究；阐明干热岩温度变化与渗透性演化特征；揭示多相渗流特性及其与变形的耦合机制；得出岩体化学反应与干热岩渗透性及热开采效率的演化规律；建立干热岩复杂裂隙岩体的热-流-固-化多物理场多相流动偶合模型与数值分析方法；提出利用超临界CO2进行开采的优化设计方案及运行参数，为我国开采干热岩地热资源提供理论和技术支持。

干热岩地热开采机理研究是国家保障能源供给，解决环境问题的重要课题，也是国际岩石力学的研究前沿，涉及高温裂隙岩体的多场耦合机理、多相渗流特性、溶蚀与结晶反应等关键科学问题。本项目建立了流动-温度-力学以及化学反应的耦合模型，并开发了基于统一管网法的复杂裂隙孔隙材料中水力多场耦合数值分析程序，研究了酸化溶蚀对突破曲线及溶蚀形态的影响。研究了裂隙空间几何形态以及水力开度对酸化的影响。研究了支撑剂的使用以及储层弹性模量和最小水平应力对热开采效率的影响。研究结果为我国开采干热岩地热资源提供理论和技术支持。