Sealing Porous Media through Calcium Silicate Reactions with CO2 to Enhance the Security of Geologic Carbon Sequestration

The injection of CO2 deep underground, i.e., geologic carbon sequestration, has attracted considerable attention for climate change mitigation. A reliable caprock for secure containment is essential, alongside strategies for sealing flow paths to prevent leaks. In this study, we explore ways in which reactions of CO2 with CaSiO3 can be used for targeted mineral precipitation and permeability control in situ. Previous work has suggested that certain CaSiO3 polymorphs can produce pore-filling precipitates that successfully inhibit flow, whereas others produce precipitates with little impact. In this work, a one-dimensional reactive transport model was developed for a centimeter-scale system to explore connections between the pore and continuum scale. The model considers four reactions involving CaSiO3, CaCO3, SiO2(am), and the crystalline calcium silicate hydrate (CCSH) tobermorite. A key feature is incorporation of microporosity, with an attempt to represent favorable volume expanding changes from CCSH precipitation in porous media. At 150°C and 1.1 MPa CO2, representing typical laboratory conditions, the model predicts significant permeability drop when reacting the pseudowollastonite CaSiO3 polymorph at elevated pH to produce CaCO3, SiO2(am), and tobermorite. The effect of increasing pH via by NaOH addition, which increases CO2 solubility, increases CaSiO3 dissolution, and supports tobermorite supersaturation. In contrast, reaction of the wollastonite polymorph results in CaCO3 and SiO2(am) formation, with limited permeability impact. Wollastonite's lower solubility and slower dissolution rate inhibits tobermorite formation. Simulation at the high pressures representative of deep subsurface field conditions (40°C and 7.5 MPa CO2) suggests that reaction of CaSiO3 with CO2 could reduce permeability and seal unwanted leakage pathways.