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

Geothermal energy is a promising emerging technology with the potential to generate energy from an almost unlimited global resource. However, its main challenge is the high cost of drilling required to access resources located at significant depths. Abandoned oil wells are an attractive alternative as they offer the potential to reduce the capital investment associated with drilling significantly. This study aims to demonstrate the feasibility of using an abandoned oil well as a source of geothermal energy. To this end, a three-dimensional numerical model of a U-tube heat exchanger has been developed and simulated based on real data from an abandoned oil well in southeastern Algeria. The objective is to provide an accurate and realistic representation of the heat flow and temperature distribution inside a heat exchanger installed in this abandoned oil well. The effects of mass flow rate, fluid inlet temperature, insulation length, and pipe diameter on the durability and performance of the U-tube heat exchanger were analyzed. In addition, a constant power model was proposed to evaluate a geothermal resource's sustainable heat extraction rate. The obtained results show that Borehole Heat Exchanger (BHE) performance is directly influenced by working fluid inlet conditions and the higher inlet velocities increase heat output and lower outlet temperatures, while higher inlet temperatures decrease heat output despite increasing outlet temperatures. 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.