Insights into geothermal utilization of abandoned oil and gas wells

Abandoned oil and gas wells (AOGW) with high bottom-hole temperature contain abundant geothermal energy, which can be retrofitted to a novel geothermal system for different utilizations without high-cost drilling. Thus, at recently, some researchers concentrate on evaluation of the performance of thermal energy extraction from AOGW and geothermal power generation using AOGW with Organic Rankine cycle (ORC) systems. The aim of this paper is not only to review advanced geothermal utilizations for AOGW, but also make insights into the thermal simulation methods and power generation as well as working fluids selection for AOGW geothermal system. Due to heat extraction from AOGW dominating the geothermal utilizations; firstly, this paper performed to summarize and discuss the heat transfer models of AOGW geothermal system, which involve wellbore heat transfer and transient heat conduction in surrounding formation. Then, for evaluating the performance of power generation systems using AOGW, three different power plants were compared and the influence factors were examined. In addition, the optimum selection criteria of working fluids were also summarized, and the optimal fluids for different wells were determined. At last, the summary of key problems of the AOGW geothermal utilizations were proposed, and the future development and applications of AOGW were suggested for improving the geothermal utilizations.