Mineral surface area evolution during CO2-mineral-brine reactions

Abstract:

Subsurface CO₂ sequestration is one promising means of carbon capture, utilization and storage (CCUS) to mitigate the current atmospheric CO₂ emission problem. Reactive transport modeling can be used to enhance understanding of the complex geochemical reactions induced by geologic CO₂ injection and simulate reaction systems beyond the lab scale. Accurate simulation of mineral reaction rates requires knowledge of mineral reactive surface area and the evolution of reactive surface area. However, the evolution of mineral surface areas during CO₂-mineral-brine reactions is not well understood. Currently, the commonly used theory assumes mineral grains are spherical and mineral surface areas evolve as the size of the sphere changes. However, scanning electron microscopic images reveal that majority of the mineral phases are not spheres and many grains are not entirely accessible due to grain coatings. In this work, we aim to enhance the understanding of mineral surface area evolution during dissolution reactions and to improve modeling abilities for more accurate simulations. Disaggregated Bandera Grey sandstone samples will be reacted with CO₂ saturated brine in a closed-batch system under elevated temperature and pressure. The initial mineral surface areas will be determined based on image perimeter analysis in 2D scanning electron images of thin sections. In addition, BET specific surface areas of each mineral phases will be measured before and after experiments. Effluent samples will be analyzed with ICP-OES to determine the ion concentrations differences before and after experiments. The obtained experimental results will be used to inform simulations to reproduce the observed dissolution rates in batch experiments. The current surface area evolution theory will be evaluated for different mineral phases by comparing their surface areas calculated from simulations and experiments. An improved relationship of mineral surface area, volume fraction and porosity may be developed based on these results. The application of the new relationship on other samples with varying compositions will also be evaluated in the future work.