CO2-brine interactions in anhydrite-rich rock: Implications for carbon mineralization and geo-storage

The utilization of subsurface geologic media for carbon capture and storage through mineralization has been recognized as a reliable approach. However, less attention has been given to anhydrite rock type for CO₂ mineralization and storage. Anhydrite-rich rock formations, commonly found in various geological settings, have the potential to serve as natural carbon sinks through the mineralization of CO₂. Therefore, this study aims to investigate the mechanisms and potential of anhydrite-CO₂-brine interactions for carbon storage. The experimental approach involved exposing anhydrite-rich rock to supercritical CO₂-brine environments under varying conditions of fluid composition. Mineral transformation of an outcrop anhydrite-rich rock sample in static reactor under subsurface conditions of elevated temperature (60 °C) and pressure (104 bar), in the absence and the presence of SrCl₂ was conduct for a one-month period. Mineralogical and geochemical analyses, including, solution analyses, X-ray fluorescence, X-ray diffraction, micro-computed tomography, and mechanical properties were conducted to examine the changes in the composition and rock structure resulting from the interactions. The experimental reactions revealed that anhydrite undergoes mineral transformation upon exposure to supercritical CO₂-saturated brine to form stable minerals including calcite, dolomite, magnesite, and strontianite, which contributes to the potential for long-term storage of CO₂ in the subsurface geologic media. The efficiency and extent of carbon mineralization were found to be influenced by brine composition. These findings contribute to the understanding of the potential of these formations for carbon storage, opening avenues for further research and the development of effective carbon capture and storage strategies.