Mine water for thermal energy storage – An analysis of hydrogeochemical factors based on in-situ real laboratory stations

Aquifer thermal energy storage (ATES) is a promising technique for the short- to long-term storage of reusable thermal energy in the subsurface. Many ATES projects suffer from operational issues or failures. Main causes are clogging, mineral precipitation and corrosion affecting both the aquifer matrix and technical infrastructure (e.g., pipes, heat exchangers), as well as unfavourable recovery rates due to convective and conductive heat energy losses across natural system boundaries.

While most systems address natural porous aquifers, a range of formerly active underground mines has been considered for ATES as well. The ongoing research project “MineATES” focuses on chances and limitations of such man-made systems.

Specifically, an in-situ real laboratory has been set up at the former silver mine “Reiche Zeche” in Freiberg, Germany, to simulate periodical heat exchange between mine water and surrounding rock. Hydro-/geochemistry changes will be logged simultaneously to the monitoring of heat propagation in both water and rock. In parallel, laboratory-scale flow-through column and batch experiments with multiple combinations of rock types and mine water compositions will be carried out at defined temperatures (~ 5°C to 50°C) to identify scales, types and locations of possible mineralization and further chemical alteration. Reference materials (rocks and mining waters) from the “Reiche Zeche” will be compared to materials from the Saxonian mines “Ehrenfriedersdorf” (former tin ore mine) and “Lugau/Oelsnitz” (former hard coal mine).

The project results are to be compiled into a criteria catalogue, providing guidelines for assessing if and how a mine could be used as an ATES system.