Quantifying the Impacts of Subsurface Geochemical Processes During Geothermal Operations

Understanding the geochemical effects of fluid injection and extraction on reservoir properties is critical for the success of geothermal operations, as induced water-rock interactions - such as mineral dissolution and precipitation - can significantly influence system’s performance and long-term sustainability. 

This research, developed within the frame of the THC-Prognos project, aims to investigate and validate advanced reservoir engineering concepts for geothermal utilization and management. Under the prospective of future geothermal development in the Berlin’s urban area, particularly at the TU Berlin campus in Berlin-Charlottenburg (Fig. 1), this study primarily addresses site-specific geochemical issues triggered by water circulation within a porous, unconsolidated reservoir currently investigated for Aquifer Thermal Energy Storage (ATES) porpoises. According to Regenspurg et al. (2018), these processes are likely linked to the oxidation of pyrite, leading to the release of sulfuric acid and iron (Fe) ions. The resulting acidification of the reservoir promotes the dissolution of aluminum-silicates, which in turn releases substantial amounts of aluminum (Al)—a compound that is poorly soluble under the nearly neutral pH conditions typical of the target reservoir in its undisturbed state.

These processes are of high relevance from an operational point of view, as the mobilization of Al and Fe ions pose the risk of pore clogging due to their reprecipitation in the shape of alteration minerals, which may negatively affect the site-specific ATES performance over time. Integrating flow-through experiments and fully coupled THC modelling - using the newly developed GOLEM-PHREEQC interface for 3D multiphysics reactive transport in heterogeneous, complex reservoirs (Fig. 2) – this research seeks to assess and quantify such impacts in terms of alteration of reservoir parameters (e.g., porosity and permeability) and overall system’s performance.