Delineation of the thermal plume associated with a standing column well system in a fractured aquifer using numerical modeling

Abstract

Standing column wells mostly recirculate groundwater in uncased wells. To enhance their thermal performance, a fraction of the flow can be diverted into one or more nearby injection well, which promotes advective heat transfer and can lead to the development of a thermal plume. The thermal plume may affect the capacity of the ground to supply heat and thereby impact the sustainability of a ground-source heat pump system. The effect of fractures on a thermal plume, as well as the potential conflicts of use arising from the operation of a standing column well system, were assessed for a fractured geological environment. A 3D finite-element model was used to simulate the thermal plume of a real ground-source heat pump system consisting of five standing column wells and one injection well at an elementary school located in Mirabel, Canada. The horizontal extent of the thermal plume is approximately 40 m by 45 m over a surface area of 1600 m${}^2$ and the temperature anomalies are more prominent between the standing column wells and the injection well. The study also reveals that permeable fractures are associated with the maximum horizontal extent of the thermal plume and are therefore particularly important to consider in dense and urban areas, where the risk of interference is higher. Moreover, it is shown that productive fractures control thermal feedback and ground temperature recovery and, hence, need to be taken into account to properly design and evaluate the actual performance and sustainability of a standing column well system.