Effects of fracture evolution and non-Darcy flow on the thermal performance of enhanced geothermal system in 3D complex fractured rock

Abstract

In fractured geothermal reservoirs, the fracture networks and internal fluid flow behaviors can significantly impact the thermal performance. In this study, we proposed a non-Darcy rough discrete fracture network (NR-DFN) model that can simultaneously consider the fracture evolution and non-Darcy flow dynamics in studying the thermo-hydro-mechanical (THM) coupling processes for heat extraction in geothermal reservoir. We further employed the model on the Habanero enhanced geothermal systems (EGS) project located in Australia. First, our findings illustrate a clear spatial-temporal variation in the thermal stress and pressure perturbations, as well as uneven spatial distribution of shear failure in 3D fracture networks. Activated shear failure is mainly concentrated in the first fracture cluster. Secondly, channeling flow have also been observed in DFNs during heat extraction and are further intensified by the expansion of fractures driven by thermal stresses. Moreover, the combined effect of non-Darcy flow and fracture evolution triggers a rapid decline in the resulting heat rate and temperature. The NR-DFN model framework and the Habanero EGS’s results illustrate the importance of both fracture evolution and non-Darcy flow on the efficiency of EGS production and have the potential to promote the development of more sustainable and efficient EGS operations for stakeholders.

Keywords

• Coupled THM model
• Non-Darcy flow
• Deformable DFN
• Enhanced geothermal systems