Carbonate aquifers for thermal energy storage: A critical analysis of clogging and scaling using temperature-controlled batch and column experiments

Throughout the past two decades, aquifer thermal energy storage (ATES) has grown increasingly into focus as a suitable geo-energy storage method. In this context, many carbonate aquifers are useable for storing and later retrieval of thermal energy due to their potential natural porosity and adequate permeability. However, numerous ATES projects suffer from operational and maintenance issues or failures. For instance, a reduction in reservoir permeability and clogging (caused by scaling, sintering, flocculation, and microbial growth) belong to the main threats to sustainable and reliable functioning.

In the BMBF-funded research project “UnClog-ATES”, both the aforementioned threats and their practical countermeasures (e.g., adding scaling inhibitors, acids, CO₂) are thoroughly investigated using a combination of flow-through column and batch experiments. These experiments are temperature-controlled to simulate realistic ATES cycles of alternating heating and cooling while monitoring them continuously.

A critical point when assessing ATES systems specifically for carbonate aquifers is that significant inconsistencies exist regarding the kinetics and intensities of mineral dissolution/precipitation processes observed in the laboratory (using pure/synthetic minerals) and those observed in reality. This is because factors such as specific surface, dislodgement from equilibrium, presence of inhibitors as well as the rock’s chemical purity play important roles. For that reason, i.e., to represent natural ATES materials and to gain realistic reaction data, limestone from the Malm (Upper Jurassic), Germany (“Treuchtlinger Marmor”), is used for our experiments.

The overall project results aim towards gaining a variety of insights that are essential for planning, effective implementation, and sustainable operation of ATES in carbonate aquifers.