Techno-Economic Analysis of Repurposing Depleted Oil and Gas Wells for Geothermal Energy

Abstract Addressing the growing global energy demand requires innovative utilization of existing resources to enhance energy supply sustainably. Depleted oil and gas reservoirs in conventional and unconventional formations offer a promising opportunity for geothermal energy extraction due to their accessibility and existing well infrastructure. This study presents a comprehensive techno-economic analysis to evaluate the feasibility, efficiency, and economic impact of repurposing abandoned wells for geothermal energy production through integrating geological characterization, thermal-hydraulic modeling, and economic assessment. This study investigated the common practices for geothermal coaxial closed-loop configurations in conventional and unconventional formations. The conduced investigation provides a comprehensive parametric sensitivity analysis that evaluates the impact of key reservoir and operational parameters on outlet temperature and thermal power output. The analysis focused on five critical variables: injection rate, injection temperature, formation thermal conductivity, lateral well extension, and the bottom-hole temperature. Additionally, economic analysis of direct-use applications under varying operational and reservoir conditions was employed. The findings of this study confirm that both vertical and horizontal repurposed hydrocarbon wells can be technically and economically viable for direct-use geothermal applications. The analysis highlights several critical factors influencing the thermal and economic performance of these systems: flow rate, injection temperature, and formation thermal conductivity. The study demonstrates that flow rate is a primary control on thermal output, but its effect is heavily dependent on well geometry. The vertical well shows an operational sweet spot around 23 kg/s, after which thermal breakthrough causes a decline in performance. In contrast, the horizontal well exhibits continuous thermal power growth, achieving more than three times the peak output of the vertical well due to the larger heat exchange surface. This geometric advantage translates directly into enhanced economic performance, with the horizontal configuration maintaining a significantly lower Levelized Cost of Heat (LCOH) of approximately $40/MWh compared to the vertical system with $95/MWh at its optimum. The results also underscore the importance of maintaining an optimal injection temperature and targeting formations with high thermal conductivity. An increase in injection temperature was found to reduce the value of the project, particularly in the less efficient vertical system, where LCOH rose by over $40/MWh. Conversely, higher formation thermal conductivity proved to be a powerful screening criterion, as it substantially reduced LCOH in both systems—by approximately $50–60/MWh in the vertical case and $25/MWh in the horizontal case. The final analysis compellingly shows that while a higher bottom-hole temperature contributes a moderate 27–30% to thermal performance, the lateral extension of a horizontal well is the dominant factor, yielding a remarkable 121–127% improvement in thermal output. This finding provides crucial guidance for the future selection and design of geothermal projects from repurposed oil and gas wells, underscoring the superior potential of horizontal drilling infrastructure. This study contributes valuable insights for optimizing geothermal energy recovery and underscores the horizontal well configuration as a highly effective model for future applications.