Thermo-economic performance of a leaky downhole coaxial geothermal system for maximizing geothermal energy production: Numerical investigation

The low heat extraction rate is one of the crucial bottlenecks of hydrothermal geothermal recirculating wells. The leaky downhole coaxial geothermal system has recently been considered a promising heat extraction approach with the advantages of a high heat extraction rate and low investment cost, especially suitable for medium-low hydrothermal geothermal reservoirs. To assess the heat extraction improvement of the leaky downhole coaxial geothermal system over the traditional single aquifer open loop geothermal systems. This study evaluates the leaky downhole coaxial geothermal system (LDCGS), highlighting its potential for higher heat extraction rates and cost efficiency in medium-low hydrothermal geothermal reservoirs. We developed a comprehensive thermo-economic model to assess the LDCGS, enhanced with a packer, against traditional open loop system and a checkboard pattern doublet system, over a 30-year operational period. Additionally, a sensitivity analysis is also conducted to figure out the system parameters including; permeability ratio, reinjection layer thickness, aquitard layer thickness, reinjection temperature, and flow rate on the heat transfer extraction rate. Findings reveal optimal conditions for reservoir design to be a permeability ratio ≥20, flow rate of 50 m3/h, and reinjection temperature of 15 °C, for heat extraction maximization. Conclusively, LDCGS with a packer demonstrates superior thermal performance and economic feasibility, with a calculated payback period of 14.26 years, positioning it as an advantageous approach for hydrothermal geothermal applications.