De-Risking Geochemical/-Mechanical Impacts of the Injection and Storage of Impure CO2 in a Carbonate Reservoir

Before a CO2-storage project can be initiated, any potential geochemical impacts of CO2-injection and storage need to be evaluated and de-risked. This is particularly relevant for alternative lithologies, such as carbonates, which may be more reactive with both CO2 and impurities. In this study, we carried out a first geochemical risk assessment for CO2-injection and -storage in two carbonate-hosted saline aquifers. First, we considered the main potential impacts on the reservoir of CO2 itself, such as mineral dissolution, and salt precipitation due to brine evaporation. Next, we assessed the key potential impacts of impurities, including (further) enhanced mineral dissolution and enhanced precipitation. Enhanced precipitation may result from interactions between injected impurities and reservoir minerals, e.g., when impurities such as SOx cause enhanced dissolution of calcite, followed by the precipitation of CaSO4. In addition, precipitation can also be enhanced by scale formation through direct interactions between the injected impurities and dissolved components in the reservoir brine. Based on this assessment, we identified salt precipitation and scale formation as the key challenges to efficient CO2-injection and storage, requiring further study to de-risk.