Analysis of the Performance of Abandoned Oil Wells Converted To Geothermal Heat Exchangers for Energy Production

Geothermal energy is a promising technology that can harness an abundant and sustainable resource for large-scale energy generation. This study investigates the thermal behavior of a deep borehole heat exchanger (DBHE) with a depth of 3030 m, located in Algeria. The analysis is based on a numerical model developed using ANSYS-CFX to simulate fluid–soil heat transfer over long operating periods. The borehole is modeled as a U-tube heat exchanger inserted into a stratified geological formation with distinct thermophysical properties. Simulation results reveal that the soil temperature decreases gradually during the first years of operation, and the system reaches quasi-steady-state conditions after approximately five years, as the rate of temperature decline becomes negligible. The influence of flow velocity and inlet temperature on the thermal performance of the system is also investigated. Results demonstrate that increasing the flow velocity enhances heat extraction, while lower inlet temperatures significantly improve the long-term stability of the exchanger. A simulation with a 3030 m depth, 0.01 m diameter, 303.15 K inlet temperature, and 0.5 m/s inlet velocity predicted a 366 K outlet temperature after five years. This work highlights the potential of deep abandoned oil wells in Algeria to be repurposed for geothermal applications, contributing to the diversification of sustainable energy resources.