ALTERATION OF PHLOGOPITE SURFACES IN SUPERCRITICAL CO2 SATURATED SALINE WATER

To effectively apply geological CO₂ sequestration, a better understanding of the interactions between rock and CO₂ saturated saline water is necessary. While macroscale studies of the long-term reactions between CO₂ and rock samples can provide useful information, knowledge of microscale changes over shorter reaction times is also essential to understand both the evolution of pore sizes and geochemical reactions in CO₂ geologic sequestration. In this work, we sued both chemical analysis and interfacial topographic studies to investigate the dissolution of phlogopite (KMg₃Si₃AlO₁₀(F,OH)₂ ), which served as a model of clay minerals that are present in both formation rocks and caprocks in potential CO₂ sequestration sites. We observed phlogopite dissolution incurred by the introduction of CO₂, as evidenced by the elevated concentration of Al, Mg, Si, and K in 1 M NaCl solution that simulated saline water. Nanoscale precipitation of secondary mineral phases occurred on phlogopite surfaces after 5 hours, based on atomic force microscopy (AFM) images. Ellipse-shaped nanoscale particles first appeared on the edges of dissolution pits and then relocated to other areas. The formation of nanoscale precipitation after short reaction times, together with the relocation of those particles, suggests that although the porosity of rocks (porous media) may not change significantly, the permeability of the rock can be changed by pore throat clogging. Therefore, the transport pathway and fate of CO₂ could be altered. In this presentation, we also discuss the effects of salinity on the interactions of CO₂-water-rock. This research provides new key information on the kinetics and mechanisms of the interfacial reactions between CO₂ and sequestration rocks. This information will aid in designing secure and environmentally acceptable CO₂ sequestration techniques.