A three-dimensional coupled thermo-hydro model for geothermal development in discrete fracture networks of hot dry rock reservoirs

Three-dimensional (3D) fluid flow and thermal transport modeling in discrete fracture networks (DFNs) is critical for geothermal energy recovery from enhanced geothermal systems (EGSs). Considering nonlinear fluid flow models, a 3D coupled thermo-hydro (T-H) model based on the Galerkin finite element method was developed for DFNs. Forchheimer flow was considered in this fluid flow model, and a simplified thermal transport model was adopted based on the local thermal non-equilibrium theory. Finite element spatial discretization of fluid flow and thermal transport models in DFNs was formulated. A sim-ple upwind scheme was adopted as the numerical strategy of the thermal transport model, avoiding its solution oscillation. In addition, the proposed numerical method for the fluid flow and thermal transport was verified by comparing the model results with experimental, analytical, and numerical solutions. This approach was further applied to the modeling of heat extraction in a Habanero EGS reservoir for a period of 40 years under different injection pressures. The results demonstrated that the proposed approach was effective for simulating coupled T-H processes in 3D DFNs. With increasing the injection pressure, the power generation of reservoir increased, but its life span decreased. Injection temperature had positive effect on life span for power generation.(c) 2022 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Automated summary

Three-dimensional fluid flow and thermal transport modeling in discrete fracture networks (DFNs) is crucial for enhanced geothermal systems (EGSs). A coupled thermo-hydro (T-H) model based on the Galerkin finite element method was developed, considering nonlinear fluid flow models and a simplified thermal transport model. The proposed method was validated using experimental, analytical, and numerical solutions, and applied to simulate heat extraction in a Habanero EGS reservoir. The results showed that injection pressure and temperature had different effects on power generation and reservoir lifespan.