Parametric study of coaxial deep borehole heat exchangers to determine peak performance and zone of influence

Pap, József and Baracza, Mátyás Krisztián (2024) Parametric study of coaxial deep borehole heat exchangers to determine peak performance and zone of influence. GRADUS, 11 (3). ISSN 2064-8014

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Abstract

Heat production from abandoned oilfield wells retrofitted into coaxial deep borehole heat exchangers (DBHEs) have become a hot topic in the past decade, since the utilization of geothermal energy drew increased attention due to the volatility of the energy prices. Numerous studies investigate performance enhancement possibilities of such systems, all agreeing that the circulation rate is one of the strongest driving factors which influences total thermal output and sustainability. While these wells have several stages of cemented casings in the wellbore, each having size limitations on the production string, the annular and string cross-sectional flow areas, thus velocities of the countercurrent fluid streams could greatly influence the total heat output of the selected arrangement. Moreover, with each setup, heat contact surface between the formation and the parallel fluid columns changes, furtherly influencing the performance. This paper introduces a numerical model, where the authors have investigated several well structures under various circulation rates to determine optimal flow rate under continuous operation.

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