Decoupling thermo-hydraulic processes from chemical reactions to understand the effect of heat on chemical reactions

Changes in temperature can modify the geochemistry of groundwater. This effect is very relevant not only for natural geothermal phenomena, but also for geothermal energy systems and Underground Thermal Energy Storage (UTES) systems. We propose a novel method that can be used to verify sophisticated numerical models and understand the thermo-hydro-chemical (THC) processes more clearly. The method decouples the chemistry from the thermo-hydraulic (TH) processes. The chemistry is obtained from geochemical batch calculation by PHREEQC and the TH processes from the finite element code CODE_BRIGHT. The method has been applied to a UTES pilot project near Bern, Switzerland, and compared with the THC coupled code RETRASO. The good agreement between the presented method and RETRASO verifies the correct implementation of our method. Moreover, the results provide information about the dominant reactive transport processes, mineral reaction rates and porosity changes.

Acknowledgements: This work was financed by the ERANET project HEATSTORE (170153-4401). This project has been subsidized through the ERANET cofund GEOTHERMICA (Project n. 731117), from the European Commission, RVO (the Netherlands), DETEC (Switzerland), FZJ-PTJ (Germany), ADEME (France), EUDP (Denmark), Rannis (Iceland), VEA (Belgium), FRCT (Portugal), and MINECO (Spain). Also, the first author is supported by a grant from the Department of Research and Universities of the Generalitat de Catalunya (2022 FI_B1 00208).