Design optimization of Deep Borehole Heat Exchangers (DBHEs) for well retrofitting

This study demonstrates the potential of Deep Borehole Heat Exchangers (DBHEs) technology to unlock low-risk, cost-effective geothermal energy in Groß Schönebeck by repurposing existing wells. The well doublet features approximately 1.5 km of the Zechstein formation, a thermally conductive and impermeable formation ideal for DBHE applications. A numerical simulation using CMG STARS was used to optimize the installation of a DBHE to a depth of 3800 m MD. At this completion depth, both wells achieved thermal power ranging from 500–750 kilowatts (kW) and outlet temperatures in the range of 49–67 °C with the flow rates ranging from 10 to 25 m 3 h −1 and inlet temperatures between 10–25 °C. With the model, we explored the relationship between tubing dimensions and materials, as well as the impact of varying operational parameters on the performance of the DBHEs. Our analysis confirms direct heating is the most suitable application, with a Levelized Cost of Heat (LCOH) of 7-14 ct €/kWh within the given operational parameters. While electricity generation is not feasible, the study highlights a cost-effective, low-risk geothermal heating solution by repurposing existing wells as DBHEs. Key requirements include deployment of minimum 2.88”/2.44” (OD/ID) vacuum-insulated tubing (or equivalent) with low thermal conductivity ( ≤ 0.06 W m −1 K −1 ), and subsequent field validation of heat transfer parameters. This approach minimizes investment and risk by utilizing existing infrastructure, but requires close proximity between the heat source and the consumer. Future research and feasibility studies should prioritize well integrity and seamless integration with surface infrastructure and district heating networks. • The first closed-loop system modeling for Groß Schönebeck. • Review of the latest DBHEs technology development. • Well design optimization for the existing well doublet. • Workflow and economic assessment of DBHEs technology implementation.