The Nanoscale Basis of CO₂ Trapping for Geologic Storage

Carbon capture and storage (CCS) is likely to be a critical technology to achieve large reductions in global carbon emissions over the next century. Research on the subsurface storage of CO₂ is aimed at reducing uncertainties in the efficacy of CO₂ storage in sedimentary rock formations. Three key parameters that have a nanoscale basis and that contribute uncertainty to predictions of CO₂ trapping are the vertical permeability k_v of seals, the residual CO₂ saturation S_g,r in reservoir rocks, and the reactive surface area a_r of silicate minerals. This review summarizes recent progress and identifies outstanding research needs in these areas. Available data suggest that the permeability of shale and mudstone seals is heavily dependent on clay fraction and can be extremely low even in the presence of fractures. Investigations of residual CO₂ trapping indicate that CO₂-induced alteration in the wettability of mineral surfaces may significantly influence S_g,r. Ultimately, the rate and extent of CO₂ conversion to mineral phases are uncertain due to a poor understanding of the kinetics of slow reactions between minerals and fluids. Rapidly improving characterization techniques using X-rays and neutrons, and computing capability for simulating chemical interactions, provide promise for important advances. (Figure Presented).