On the application of silica gel for mitigating CO2 leakage in CCS projects: Rheological properties and chemical stability

Silica sol gels have the potential to act as sealing agents to reduce leakage risks associated with long-term CO2 storage. This study considers the effects of brines of varying chemical composition on the formation of sol gels, their viscosity, and their long term stability. The gelation times of sol-gel solutions were measured for different concentrations of SiO2 , Na+, K+, Ca2+, and Mg2+ as well as pH levels. Individually, increased concentrations of SiO2, Na+, K+, Ca2+, and Mg2+ reduced gelation time. However, the combined effects of Nat, HCl, and Ca2+ or Mg2+ were found to delay gelation, compared to when only Ca2+ or Mg2+ is added. Gelation times were similarly found to be a complex function of the pH of the system. Empirical fits were obtained describing the gelation times and the precursor sol viscosities from the start of activation until gelation. Expressions are presented that relate the changes in the fitting parameters in response to variations in gel composition. There is good agreement between the experimental measurements and the models, which could be used to predict gelation rates in field-scale applications. The durability of the gel was also investigated through experiments in which the gels were exposed to different solutions of varying salinity and pH. These results showed that silica gels were stable after 45 days of brine exposure, with the most significant change being a slight expansion of the gel. Additional experiments revealed that the gels remained thermally stable for expended periods at a temperature of 60 degrees C.

Automated summary

This study investigated the effects of varying chemical compositions on the formation, viscosity, and stability of silica sol gels. It found that factors such as concentrations of SiO2, Na+, K+, Ca2+, Mg2+, and pH levels all play a role in gelation times, with complex interplay between these variables influencing the process. Additionally, empirical fits were obtained to describe the gelation times and precursor sol viscosities, showing good agreement between experimental measurements and models for predicting gelation rates in real-world applications.