There are many oil and gas wells globally which are not used for production, injection or other purposes. By converting abandoned or non-activated oil and gas wells to geothermal wells, it would be possible to defer plug and abandonment costs and produce geothermal energy. As a crucial stage for the claim verification and eval-uation of feasibility or efficiency of this conversion, it is important to be aware of the practical and simulation studies in the literature. Therefore, this work presents a comprehensive overview and analysis of 20 case studies published from different countries, followed by analysis of formations, important downhole and surface parameters. In terms of downhole, production scenarios either open-loop or closed-loop, optimization of open-loop systems, borehole heat exchangers with their different types and dimensions, insulations, positive hydraulic and thermal advan-tages of installing bottomhole curvature, are covered. Next, organic Rankine cycle (ORCs), selection of circu-lation fluids, circulation rates, and working fluids are covered, followed by the produced and net energies coefficient of performance (COP) and thermal efficiency. Finally, a recommended idea applicable to super-highly pressured aquifers is presented in an example case study. This investigation shows there is good potential for using geothermal energy from abandoned and old petroleum wells.
