Investigation on Heat Extraction Performance of Fractured Geothermal Reservoir Using Coupled Thermal-Hydraulic-Mechanical Model Based on Equivalent Continuum Method

Abstract

Natural fractures and artificial fractures in a tight rock matrix of an enhanced geothermal system make flow and heat transfer become seriously anisotropic. In this paper, a field-scale fractured heterogeneous geothermal reservoir model is built to study the heat transfer process. Based on an equivalent continuum method and local thermal non-equilibrium model, an equivalent permeability tensor is mapped from discrete fractures and a coupled thermal-hydraulic-mechanical mathematical model is adopted in which logarithmic stress sensitivity model is used to couple effective stress and permeability. From numerical simulation results at different injection rates, the contour results show the heterogeneity of flow, heat transfer and stress sensitivity are dominated by fractures distribution. Temperature contours reveal that the heat convection between water and rock in a fracture is more intense than the heat conduction between rock under different temperatures. The predicted power generation of a geothermal plant reveals the adverse effect on heat conversion efficiency, which is caused by the temperature drop at high injection rates.