Protecting geological carbon dioxide (CO2) storage over the long term requires robust barrier mechanisms to prevent fluid escape and protect sensitive ecosystems. While intact caprock formations serve as the primary containment mechanism, chemical reactivity in the subsurface provides an additional safeguard against CO₂ migration. Within the framework of the GEOSTOR project (Submarine CO2 Storage in Geological Formations of the German North Sea), we investigated the feasibility of reactive geomaterials (CaCO₃, olivine, clay minerals) as mitigation strategies in the event of barrier failure. Our study employed a thermo-hydro-chemical-mechanical (THCM) approach, integrating experimental and modeling techniques to assess barrier performance under realistic storage conditions. Our focus was on reactive barriers at the seafloor, with potential applicability in deeper subsurface environments through microbial carbonate precipitation approaches.
Experimental studies included batch dissolution and flow-through column experiments under controlled in situ conditions (CO₂ partial pressures up to 10 bar). Our results demonstrated that reactive barriers could effectively neutralize CO₂-rich fluids, achieving Ca²⁺ concentrations of ~40–50 mM and alkalinity levels of 80–100 meq L-1, confirming the feasibility of kinetic CO₂ conversion. Observations further revealed dissolution-driven pore water replacement, promoting a sustained exchange of buffered fluids essential for counteracting acidification in benthic ecosystems.
The technical application of reactive barriers is particularly relevant for mitigating CO₂ leakage along abandoned oil and gas wells, which represent potential migration pathways in storage formations. Comparable methane leakage from shallow accumulations in the North Sea has been previously observed, highlighting the need for proactive containment strategies. Our findings suggest that engineered reactive barriers offer a promising approach to stabilizing CO₂ leakage sites, providing an additional safeguard in CO₂ storage projects. Further research is required to optimize material selection and long-term stability, ensuring effective deployment in diverse geological settings.