超临界CO2在高温裂隙岩体中的热交换研究

近年来,由于超临界CO₂(Supercritical CO₂,简称scCO₂)额外的地质封存效益,将scCO₂替代水,作为深部地热开采的工作流体的设想,正受到越来越多的关注。因此,开展高温裂隙岩体中流体运动和热交换过程的模拟研究,对于理解深部地热开采机理具有重要意义。本文在充分考虑scCO₂热物理性质随压力和温度变化的基础上,建立了基于三维裂隙网络显式描述的复杂高温裂隙岩体scCO₂热-流耦合模型。通过与热流耦合作用下的二维单裂隙模型的解析解进行对比,验证了数值模型的正确性,然后对scCO₂在复杂三维随机裂隙岩体的渗流和热交换过程进行了模拟。研究发现:贯通的裂隙网络通道是scCO₂的主要流动路径,在贯通的裂隙簇中会出现明显的优势流,突破现象最早在贯通裂隙簇中产生,scCO₂流体对压力非常敏感,选择合适的注入压力能显著增加热交换效率和降低流动难度。模拟结果表明,本模型可以很好地展现裂隙岩体换热过程的非均质特性和结构面控制特性,可作为评价scCO₂采热过程的有效工具。

Study on the Heat Exchange of Supercritical CO2 in High Temperature Fractured Rock Mass

In recent years, due to the additional geological storage efficiency of supercritical CO₂ (scCO₂), the idea of replacing scCO₂ with water as a working fluid for deep geothermal mining is receiving more and more attention. Therefore, the simulation study of fluid motion and heat exchange process in high temperature fractured rock mass is of great significance for understanding the mechanism of deep geothermal mining. Based on the consideration of the thermophysical properties of scCO₂ with pressure and temperature changes, the scCO₂ heat-flow coupling model of complex high temperature fractured rock mass based on three-dimensional fracture network was established. Firstly, the correctness of the numerical model was verified by comparing the analytical solutions of the two-dimensional single-fracture model under the coupling of heat flow. Then, the seepage and heat exchange process of scCO₂ in complex three-dimensional random fractured rock mass was simulated. It is found that the through-fracture network channel is the main flow path of scCO₂, and there is obvious dominant flow in the through-fracture cluster. The breakthrough phenomenon first appears on the through-fracture cluster. ScCO₂ fluid is very sensitive to pressure, and selecting the right injection pressure can significantly increase the heat exchange efficiency and reduce the flow difficulty. The simulation results show that the model can well show the heterogeneity and structural surface control characteristics of the heat transfer process of fractured rock mass, and it can be used as an effective tool to evaluate the heating process of scCO₂.