Hydrochemical simulation of a high-temperature aquifer thermal energy storage (ATES) system

The objective of this study was to investigate the coupled thermal¿geochemical interactions of minerals under Aquifer Thermal Energy Storage (ATES) conditions representative of the Badenian and Sarmatian horizons in the Vienna Basin. Geochemical simulations were per-formed using the Terranta software to reproduce formation-specific hydrochemical condi-tions and mineralogical compositions. A schematic two-dimensional model was developed to represent a complete ATES operational cycle, including alternating winter (discharging) and summer (charging) phases. The simulations evaluated the behaviour of silicate and carbonate minerals under different reaction regimes, with silicate phases modelled using kinetic rate laws and carbonate phases treated under thermodynamic equilibrium conditions. The results indicate a pronounced con-trast between the two mineral groups. Silicate minerals exhibit limited reactivity over the investigated seasonal timescale and therefore have a minor influence on short-term system evolution. In contrast, carbonate minerals dominate the geochemical response and control the short-term mineral¿fluid interactions. The most significant geochemical reactions, primarily mineral dissolution, occur within the hot reservoir zone surrounding the injection well. Additional carbonate precipitation is ob-served in the surface heat-exchanger zone, while the cold reservoir region around the produc-tion well exhibits the lowest overall reactivity, with only minor carbonate precipitation. These spatially variable reactions are governed by temperature changes and advective mass transport and may partially compensate each other over a single operational cycle. This study highlights the importance of carefully defining geochemical boundary conditions and conceptual system schematics, as mineral reactions in ATES systems are not generic and may exhibit opposing behaviour depending on the initial conditions. The presented model-ling approach provides a realistic framework for assessing mineral reactivity under cyclic thermal loading and supports site-specific feasibility evaluations of HT-ATES systems.