Open-loop geothermal heating by combined extraction–injection one-well systems: A feasibility study

•We investigated the feasibility of one-well systems for geothermal purpose.•We performed a parameter study using a numerical flow and transport model.•Results show that a thermal short-circuit can be avoided in most cases.•One-well systems turned out to be feasible for thermal groundwater utilization.•This technical solution is most attractive in urban settings with limited space.

The feasibility of combined extraction–injection one-well systems for geothermal groundwater utilization was evaluated by means of a numerical parameter study. One-well systems require little space, but it is critically important to avoid circulation flow resulting in a thermal short circuit. Numerical models of groundwater flow and heat transport were performed to check the influence of various hydrogeological and technical parameters. Results show that circulation flow can be avoided in most cases, mainly when hydraulic gradients and conductivities are high and when the distance between the two well screens is sufficient. One-well systems are thus favourable options in urban sand-and-gravel aquifers.