SUPERCRITICAL CO2-BRINE-CLAY MINERAL INTERACTIONS AND THEIR IMPACTS ON POROSITY AND PERMEABILITY IN GEOLOGIC CO2 SEQUESTRATION

Understanding the shape, size, location, and phase of secondary minerals during the early period of CO₂ injection in geologic CO₂ sequestration (GCS) is crucial, because they could affect how the permeability and wettability of rocks will change. In this study, we investigated the mechanisms and kinetics of reactions at supercritical CO₂–water(brine)-clay mineral interfaces at molecular scale. Phlogopite and Biotite served as models for clay minerals (Mg and Fe-containing mica) that are present in both formation rocks and caprocks in potential CO₂ sequestration sites. By incorporating aqueous chemistry with synchrotron-based in situ x-ray scattering and high resolution x-ray diffraction, atomic force microscopy, and scanning electron microscopy with energy dispersive X-ray spectroscopy, we monitored in situ and ex situ nanoscale morphological evolutions resulting from dissolution of pre-existing clay minerals and precipitation of new mineral phases. The formation of nanoscale amorphous silica precipitation at phlogopite surface were observed after short reaction times (as short as 5 h), together with the relocation of those particles, suggests that the permeability of the formation rock can be changed by pore clogging. Interestingly, in biotite systems, connected dissolution pits as well as fracture-filling by extensive newly formed iron oxide nanoparticles were observed within several hour reaction time. This study provides important fundamental information for designing a more accurate reactive transport model as well as understanding pore clogging in geo-media and self fracture-filling capability in caprocks under GCS conditions.