Numerical analysis of coupled thermal–hydraulic processes based on the embedded discrete fracture modeling method

Abstract

The enhanced geothermal system (EGS) technology is considered an effective way to extract energy from deep hot dry rock (HDR) geothermal resources, which involves the coupling of complex thermal–hydraulic processes in fractured geological media. In this work, we propose a numerical approach based on the concept of embedded discrete fracture modeling method (EDFM), to estimate heat production performance from the EGS. We validated the method by comparing the outputs of our numerical models with experimental data and analytical solutions. A simplified, idealized two-dimensional model with discrete fractures was applied to gain insights on mass and heat transfer mechanisms expected under field conditions. Simulation results indicated that isolated and dead-end fractures have little influence on the overall performance of EGS, under the initial and boundary conditions of our numerical experiments (e.g., fracture density and permeability differences between fractures and matrix). It emerges that geometry and hydraulic transmissivity of fractures are key factors in controlling the effectiveness of the heat exchange between host rocks and circulating fluids. This work emphasizes the importance of implementing increasingly reliable descriptions of the fluid-dynamic and thermodynamic behavior of fractures, to increase the confidence in the numerical assessment of the performance of EGS installations.