Utilization of Discrete Fracture Network (DFN) in Modelling and Simulation of a Horizontal Well-Doublet Enhanced Geothermal System (EGS) with Sensitivity Analysis of Key Production Parameters

Abstract

Projects that feature unconventional geothermal systems are complex and come at great investment risk and high project cost. The purpose of this work is to present a method for modelling an enhanced geothermal system (EGS) that utilizes a horizontal well-doublet setup. The proposed wells’ positioning was to minimize one of the biggest cost factors: the flow rate. As a part of the research, a case study was conducted and a fully coupled EGS model prepared, based on the data from the Utah FORGE site. The model includes a discrete fracture network (DFN) that represents hydraulic fractures and a stimulated reservoir volume (SRV) for controlling the fractures’ properties. The model’s viability was checked by a series of reservoir simulations, which provided the results for sensitivity analysis of the production parameters. Analysis of the results was conducted based on the temperature decline over an EGS system lifetime, which is one of the primary indicators for EGS. The proposed solution allowed for effectively minimising the injection and production flow rate while maintaining reasonable temperature drawdown levels. It was proven that reservoir modelling and simulation tools, used in the oil and gas industry, can be successfully applied for modelling geothermal systems.

Review of discrete fracture network characterization for geothermal energy extraction

“…In fact, in a variety of EGS projects, a DFN is used to estimate the permeability in three dimensions by defining the tensor. Then, this information on the permeability tensor can be transferred to EPM models that will be anisotropic for flow applications in geothermal reservoirs of medium and high enthalpy nature (Janiga et al, 2022;Ma et al, 2022). Some of the techniques described in this research to inform DFN models are common to the rock mechanics sector due to the importance of rock discontinuities on the stability of rock engineering infrastructures (Shang et al, 2016;Schilirò et al, 2022), the excavation of rock caverns for the storage of liquefied natural gas (Xiao et al, 2019), and the mining and oilandgas sectors where fractures play a role in the extraction of fluids (Bauer and Tóth, 2017).…”