SILICATE CARBONATION IN WATER-BEARING SUPERCRITICAL CO2: NEW HINTS FOR CONNECTING LABORATORY RESULTS TO FIELD SITES

The performance of geologic CO₂ sequestration (GCS) can be affected by chemical alternations induced by supercritical (sc) CO₂–water–mineral interactions. Silicates can react with water-bearing scCO₂, forming carbonates and amorphous silica, which could in turn change the porosity and wettability of formation rocks. This study investigated the effects of particle sizes, water, temperature, and pressure on the carbonation of wollastonite (CaSiO₃) in water-bearing scCO₂. We conducted experiments under conditions relevant to GCS sites: 35-93 ^oC, 25-100 bar, and 0-14000 % (more than 140 times more than needed for saturation) water saturation percentage. We found that silicate dissolution by water-saturated scCO₂ was limited by a surface coverage of amorphous silica. The thickness of the reacted layer was found to be independent of particle sizes. In addition, at smaller water saturation percentages, higher temperature, and lower pressure, the extents of reaction were smaller owing to inhibition by the amorphous silica layer. These new findings can help us address the knowledge gap between the micrometer and nanometer size particles used in laboratory studies and mineral interactions at larger scales in field sites. They also improve our understanding of the chemical alternations induced by silicate carbonation in water-bearing scCO₂ under other energy-related subsurface operation conditions.