Three-dimensional explicit fracture representation to better understand thermo-hydro-mechanical effects in enhanced geothermal reservoirs
Abstract
The United States and countries around the world face an increasing demand for energy at the same time that carbon emissions and other environmental issues are facing greater scrutiny. Geothermal energy, generating electricity using the temperature difference between the surface and the sub-surface, is an active topic of research by the US Department of Energy and other agencies around the world. Much of the existing geothermal power generation is based on existing natural hydrothermal system. These hydrothermal schemes rely on abnormally high heat flow and an existing ground water system. The concept of enhanced geothermal systems (EGS) allows geothermal energy to be produced in nearly any land location. EGS reservoirs are often below 3 km in depth and rely on some engineered permeability enhancement to be economical. This paper describes a numerical modeling capability to help better understand the interactive thermal, hydrological, and mechanical effects that control the behavior of an EGS system. A 3D discrete fracture network is explicitly represented and a combination of specialized meshing and explicit solution techniques is used make predictions of the stimulation and production of EGS reservoirs. A comparison is made between a fully-coupled model using the 3DEC software and a complimentary approach using the DFN.lab software.