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

High-temperature aquifer thermal energy storage (HT-ATES), with its high storage capacity and energy efficiency and its compatibilities with renewable energy sources, arouses broad interest. The density-driven buoyancy flow becomes more significant for HT-ATES, which may lead to a lower thermal recovery efficiency than the conventional low-temperature ATES. Thus, understanding the displacement and thermal transport processes during HT-ATES is essential for predicting and assessing the performance of HT-ATES. In this study, the governing equations for HT-ATES considering the buoyancy flow are nondimensionalized, and five key dimensionless parameters regarding the thermal recovery efficiency are determined. Then, numerical simulations are implemented to study the recovery efficiency for a sweep of the key dimensionless groups for multiple circulations and storage volumes. It is found that the displacement processes can be classified into three regimes: a buoyancy-dominated regime, a conduction-dominated regime, and a transition regime. In the buoyancy-dominated regime, recovery efficiency is mainly correlated to the ratio between the Rayleigh number and the Peclet number. In the conduction-dominated regime, the recovery efficiency is mainly correlated to the product of a material-related parameter and the Peclet number. Then, multivariable regression functions are provided to estimate the recovery efficiency using the dimensionless parameters. The recovery efficiency estimated by the regression function shows good agreement with the simulation results. Finally, well screen designs for optimizing recovery efficiency at various intensities of buoyancy flow are investigated.