Estimation of recovery efficiency in high-temperature aquifer thermal energy storage

High-temperature aquifer thermal energy storage (HT-ATES), with its high storage capacity and energy efficiency and its compatibilities with renewable energy sources, has generated widespread interest. One main criterion for a feasible HT-ATES is the thermal recovery efficiency, i.e., how much of the invested heat can be recovered. The heat lost during the HT-ATES is mainly due to the heat conduction and the density-driven buoyancy flow, which are more significant with HT-ATES compared to the conventional low-temperature ATES. Thus, understanding the fluid displacement and thermal transport processes during HT-ATES is essential for assessing the performance of HT-ATES. A group of key dimensionless parameters regarding the thermal recovery efficiency for HT-ATES are identified in this study. The numerical model is set for a typical HT-ATES based on the geological in the Burgwedel region and the designed operational parameters. Over one thousand cases are simulated for a sweep of the key parameters for multiple cycles and storage volumes, and the resulting recovery efficiency for each case is obtained. The hot water injection and displacement processes and the correlation between the recovery efficiency and the key parameters are investigated. The correlation functions are built to estimate the thermal recovery efficiency, which can be used for a quick assessment of potential HT-ATES sites when the properties of the aquifer are known.