Sealing Porous Media through Calcium Silicate Reactions with CO₂to Enhance the Security of Geologic Carbon Sequestration

The injection of CO₂ deep underground, e.g., 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. Ways in which reactions of CO₂ with CaSiO₃ can be used for targeted mineral precipitation and permeability control in situ. A one-dimensional reactive transport model was developed for a centimeter-scale system to explore connections between the pore and continuum scale. The model considered four reactions involving CaSiO₃, CaCO₃, SiO_2(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 predicted great permeability drop when reacting the pseudowollastonite CaSiO₃ polymorph at elevated pH to produce CaCO₃, SiO_2(am), and tobermorite. The effect of increasing pH via by NaOH addition, which increased CO₂ solubility, increased CaSiO₃ dissolution, and supports tobermorite supersaturation. In contrast, reaction of the wollastonite polymorph results in CaCO₃ and SiO_2(am) formation, with limited permeability impact. Wollastonite's lower solubility and slower dissolution rate inhibited tobermorite formation. Simulation at the high pressures representative of deep subsurface field conditions (40°C and 7.5 MPa CO₂) suggested that reaction of CaSiO₃ with CO₂ could reduce permeability and seal unwanted leakage pathways.