Biogeochemical processes in saline siliciclastic aquifers due to Aquifer thermal energy storage

Aquifer Thermal Energy Storage (ATES) is a highly promising technology for storing excess energy due to its high storage capacity and small surface footprint. Despite its numerous advantages, planning, approval, and application are not yet widespread in Germany. Mineral precipitation and biofilm formation can lead to clogging of wells and aquifers. In addition, changes in the physico-chemical conditions may trigger the mobilization of toxic trace elements such as arsenic. The BMBF-funded joint project UnClog-ATES aims to investigate biogeochemical processes in the subsurface that may reduce the efficiency and long-term performance of ATES systems.

Sterile and non-sterile flow-through experiments are conducted under anoxic conditions, using both siliciclastic sediments and groundwater from a potentially ATES-suitable saline aquifer in Berlin. Through laboratory studies, the project investigates the effects of temperature changes, variations, and temporary oxygen input, and analyzes changes in the chemistry, mineralogy, and microbial community of both the groundwater and aquifer. Numerical models, including reactive transport and batch models, are developed using PHREEQC. Sensitivity analyses aid in the calibration and validation of models. They provide valuable insights into the geochemical behavior of the aquifer system and its response to different scenarios or conditions, by identifying the most influential parameters. Another key objective is to determine biogeochemical indicators that can be used to forecast clogging and define practical countermeasures to prevent or mitigate adverse effects in the aquifer.

Here we present our experimental setup and first modeling results for an ATES-suitable formation located in Berlin, Germany.