How temperature-induced density and viscosity differences affect the flow distribution through well screens and may influence heat recovery of HT-ATES systems

High Temperature Aquifer Thermal Energy Storage (HT-ATES) allows the large scale seasonal storage of sustainable heat available in summer, enabling its utilization in winter, hence reducing GHG emissions. The feasibility and potential of HT-ATES systems is largely determined by its recovery efficiency. The stored groundwater, at 40 to 80 °C higher temperature than the ambient groundwater, has a relatively low density and viscosity. The differences in density and viscosity between the stored and ambient groundwater create the potential for buoyancy-driven flow to the top of the aquifer during storage, which may lead to increased heat losses during recovery as commonly observed in earlier HT-ATES studies. Conventionally, these studies assume an uniform in- and outflow distribution of water through the well screen during injection and extraction. However, as density and viscosity changes also affect the pressure state in the well and influence the flow resistance of the aquifer, the flow distribution through the well screen is potentially impacted by these changes of density an viscosity, especially at higher storage temperatures. Therefore, this study addresses the effect of density and viscosity differences on the flow distribution through HT-ATES screens during injection and extraction for relevant storage conditions, and further assesses its impact on heat recovery compared to simulations including uniform well flow distribution. Results show that, due to both density and viscosity changes at high storage temperature, the flow distribution through the well screen may be significantly changed depending on mainly the hydrogeological and well operating conditions. Compared to HT-ATES simulations with uniform flow distribution, increased thermal recovery efficiencies are observed ranging from 0 – 8% in the 5^th year of operation for the varied conditions in this study.