Perspective Chapter: Repurposing Wells for Geothermal Use – The Role of Geological Conditions on Wellbore Heat Exchanger Performance

Repurposing wells in Italian oilfields presents a significant opportunity for renewable energy production. This chapter investigates the thermal performance of coaxial and U-shaped wellbore heat exchangers (WBHEs) for geothermal energy recovery in decommissioned wells. Three sites with distinct geological characteristics—Villafortuna 1, Tempa Rossa, and Gela 38—were selected to assess the influence of site-specific factors, well depth, and exchanger design on the heat transfer process. Semi-analytical models are implemented in Python codes to evaluate the thermal profiles of the working fluid in both configurations. Results indicate that the geothermal gradient and well depth are key parameters affecting heat exchange performance, with Villafortuna 1 exhibiting the highest outlet temperature due to its elevated geothermal gradient. For specific working fluid’s flowrate values, the U-shaped WBHE consistently outperformed the coaxial system, achieving higher outlet temperatures due to an increased heat exchange surface and the inclusion of a horizontal section at maximum depth. While fluid properties and thermal conductivity were confirmed as critical parameters, pressure drop effects were not explicitly considered and warrant further investigation. The approach proposed serves as a useful methodological tool for the preliminary assessment of the feasibility of converting selected hydrocarbon wells; the described insights offer valuable guidance for improving WBHEs design and advancing geothermal energy recovery technologies, supporting the transition toward sustainable energy solutions.