Enhanced Geothermal Systems (EGS) have gained great attention since they promise to delivers geographically disperse, carbon-free energy with minimal environmental impact. Natural fracture networks have a major impact on EGS heat extraction. The objective of our model is to evaluate the impact of natural fracture networks on EGS producing temperature profiles. In this work, we apply the thermal embedded discrete fracture model (thermal EDFM) to handle thermal modeling of complex fracture networks. The thermal non-neighbor connections enable us to efficiently simulate temperature behavior within a massive complex fracture network. Our EGS model provides a high-resolution temperature evaluation since we consider the true flow and temperature behavior in each fracture without any upscaling. In this work, we compare EGS with different fracture network connectivities to analyze heat extraction performance.
In recent years, many models have been developed for geothermal applications. TOUGH2 is a general-purpose simulator for multiphase fluid flow and heat transfer in porous media. AD-GPRS (Automatic Differentiation General Purpose Research Simulator) is widely applied to simulate steam heat transfer in the EGS using an automatic difference solution scheme. However, most EGS models cannot handle the realistic features including complex hydraulic and natural fracture networks, massive fracture numbers, and corner points due to the limited model capability and model calculation efficiency. In recent years, a novel model called the embedded discrete fracture model (EDFM) is developed to efficiently model the flow between the matrix and complex fracture network (Lee et al 2001; Li et al. 2008; Hajibeygi et al. 2011; Xu et al. 2017). Moinfar et al. (2014) extended the EDFM method to 3D simulation. Cavalante Filho et al. (2015) adapted the EDFM method to the corner-point grid. Matei et al. (2017) developed a projection-based EDFM method (pEDFM). This method automatically adjusts the matrix transmissibility field in accordance with the conductivity of the neighboring fracture networks, which extends the EDFM method applications to an impermeable flow barrier. Chai (2018) developed a compartmental EDFM (cEDFM) method by splitting the matrix blocks when intersecting fractures. This method largely improved accuracy when simulating flow across instead of along the fracture. Xu et al. (2019) extended the EDFM application to the corner point. Sun et al. (2020) applied the EDFM method to thermal modeling of distributed temperature sensing process. Sun et al. (2021) applied the thermal EDFM method to model the enhanced geothermal system with horizontal wells.