Extraction of geothermal energy resources associated with abandoned oil and gas wells: benefits and limits

Abandoned oil and gas wells (AOGWs) in mature oilfields with adequate bottomhole temperature are associated with geothermal energy resources which can be used for various utilizations. In recent years, the majority of researches has been focused on the extraction of geothermal energy from AOGWs using downhole heat exchangers (DHEs), a closed-loop type of system potentially applied to harness geothermal energy from deep wells. ??In this study, we investigated selected AOGWs with the aim to evaluate the feasibility of power generation by using a DHEs. A thermodynamic model is developed by using Engineering Equation Solver (EES) software. In addition, the impacts of rock properties, geothermal gradient, geometry of downhole heat exchanger, insulation thickness, mass flow rate of working fluid, selection of working fluid on the rate of the heat extraction are investigated in the parametric study proposed. Moreover, the future performance of the system depending on rock properties is also analysed. ??The fluid of R134a has been selected as a working fluid regarding the simulations done by EES. The simulation’s results indicated the importance to take changing fluid properties along exchanger into account. Additionally, the results lead to conclude that the generation of power from AOGWs by using DHEs is strongly dependent on the geothermal gradient through the well, the length of the heat exchanger and rock conductivity.