PNNL

Abstract

Basalt reservoirs offer potential for secure and long-term carbon sequestration through mineralization, aiding in reaching net-zero emission goals. Commercial-scale deployment of this technology requires accurate reservoir simulations, necessitating a comprehensive understanding of mineral reactivity with CO2-bearing fluids under reservoir-relevant conditions. However, knowledge gaps persist regarding the microscopic and initiating mechanisms behind carbon mineralization due to limited characterization techniques available at this scale under reservoir-relevant temperature and pressure conditions. Utilizing identical location TEM and cryo-TEM, the nanoscale carbonation processes of forsterite and diopside nanoparticles in water-saturated scCO2 are revealed. Both minerals undergo preferential metal cation dissolution into a thin water film, forming porous, Si-rich amorphous layers. This supports the "leached layer mechanism" as the prominent pathway behind carbon mineralization in silicate minerals. Comparison between the amorphous layer thickness and porosity in reacted forsterite and diopside reveals the potential role of silica network connectivity on the kinetics of carbon mineralization. The crystalline carbonates, nesquehonite and aragonite, form nanocrystals the amorphous layers. These findings on the mineral dissolution and fate of carbonate-forming cations, revealed through IL-TEM methodology, can parameterize simulations utilized in field-scale demonstrations and those for commercial deployment of carbon mineralization in basalt reservoirs.