Repurposing idle wells in the North German Basin as deep borehole heat exchangers

This study investigates the feasibility to repurpose wells from gas produc-tion for geothermal closed loop application in the North German Basin (NGB). The objective is to extend the value-added chain of idle wells by re-completion as coaxial deep borehole heat exchangers as an efficient way to produce green energy without drilling new wells by saving the carbon emis-sion and costs of building a new geothermal well. With numerical models of two typical geological settings of the North German Basin (NGB) and two different completion schemes, it is possible to simulate the thermal performance over a lifetime of 30 years. The calculated heat extrac-tion rates range from 200 kW to 400 kW, with maximum values of up to 600 kW. The heat extraction is higher compared to installed deep borehole heat exchangers. Sensitivity analyses demonstrate that re-completion depth and injection temperature are the most sensitive parameters of thermal out-put determination. The heat demand around the boreholes is mapped, and heat generation costs are calculated with heating network simulations. The initial production costs for heat are comparable to other renewable energy resources like bio-mass and competitive against gas prices in 2023. This study highlights available geothermal resources’ environmental and economic potential in already installed wells. The application has almost no geological and no drilling risks and may be installed at any idle well location.