Unlocking Enhanced Geothermal Systems using Three-dimensional Fracture Network Modeling

ABSTRACT: This study aims to develop a streamlined workflow for evaluating the feasibility of repurposing late-phase or aban-doned oil and gas sites for geothermal energy production. The scope includes assessing three heat extraction methods— Discrete Fracture Networks (DFN), Engineered Geothermal Systems (EGS), and Advanced Geothermal Systems (AGS)—by integrating geological, operational, and economic data. The analysis focuses on quantifying technical viability (e.g., reservoir temperatures, fracture networks) and economic metrics such as the Levelized Cost of Electricity (LCOE). Case studies from South Texas, se-lected for their distinct lithologies and heat flow conditions, provide a practical framework for comparing these methods and guiding infrastructure repurposing decisions. The methodology combines subsurface geological, geomechanical, and thermal data from two South Texas sites to establish baseline reservoir models. For DFN systems, natural fracture networks were simulated to optimize hydrothermal fluid flow. EGS scenarios employed stochastic modeling to represent hydraulic stimulation and perfora-tion clusters, bypassing computationally intensive fracture propagation simulations. AGS systems were evaluated for conductive heat transfer in low-permeability formations. The workflow integrated structural and stratigraphic geomodeling, finite-element hydrostructural DFN simulations, and dynamic reservoir modeling to generate predictive 3D resource assessments. Economic feasibility was quantified through LCOE calculations, incorporating drilling, stimulation, and operational costs. Technical analysis revealed DFN systems as the most sustainable, achieving consistent energy production over a 30-year period under optimal fracture configurations. EGS scenarios exhibited variability in thermal output due to fracture density and cooling effects, with wider cluster spacing improving short-term efficiency but struggling with long-term thermal depletion. AGS systems, reliant solely on conductive heat transfer, demonstrated the lowest efficiency. Economically, DFN emerged as the most cost-effective (lowest LCOE), followed by EGS and AGS. The study concludes that repurposing oil/gas sites for geothermal energy is viable in regions with high heat flow (>150°C) and natural fracture networks, with DFN-based systems offering the strongest technical and economic case for prioritization. This work introduces an integrated workflow that uniquely combines reservoir modeling, fracture network simulation, and economic analysis to assess geothermal potential at oil/gas sites—a novel contribution to both geothermal and petroleum literature. By providing comparative LCOE metrics for DFN, EGS, and AGS, it offers actionable benchmarks for industry decision-makers. The stochastic EGS modeling approach simplifies fracture simulation, reducing com-putational demands while maintaining predictive accuracy. Additionally, the findings highlight the superiority of natural fracture networks (DFN) over engineered systems in long-term geothermal projects, aligning with petroleum industry expertise in fracture management and infrastructure reuse. These insights bridge geothermal energy research with practical applications in fossil fuel site repurposing.