Assessment of hydrogeochemical processes in two potential HT-ATES reservoirs in Berlin using core analysis, laboratory experiments and geochemical modelling

While the share of renewable energy in the electricity sector is steadily increasing, it has stagnated in the heat supply, despite the fact that in Berlin, for example, more than 40 % of the CO2 emissions are caused by the heating sector. Due to its ability to store large volumes in the underground while at the same time taking up little space on the surface, HT-ATES is particularly well suited for use in urban areas and can therefore contribute to the reduction of CO2 emissions. However, clogging of aquifer pores thus reducing the permeability, corrosion and mobilization of trace elements may be undesirable effects of HT-ATES.
Here, the Triassic limestones and the Jurassic sandstones were investigated as part of two Berlin ATES studies with the aim of (a) simulating the effect of HT-ATES operation on the carbonate aquifer by geochemical modelling, (b) identifying reactive mineral phases by systematic elemental analysis using a handheld XRF and (c) estimating the permeability and mobilization processes by column and batch experiments at elevated temperatures.
The results show that rapid analysis of drill cores at the drilling site provides important information on the presence of reactive mineral phases such as iron minerals, clay and carbonate content, and can therefore assist in filter placement. The mobilization of organic matter and trace elements has been observed in laboratory tests with siliciclastic sediments. The simulation of the HT-ATES operation in the saline carbonate aquifer, on the other hand, indicated carbonate precipitation due to temperature increase and degassing.