Pore-Scale Study on the Effect of SO2 on Hydrate-Based CO2 Sequestration in a High-Pressure Microfluidic Chip

Summary To mitigate the effects of greenhouse gases, the sequestration of greenhouse gases such as carbon dioxide (CO2) in seafloor sediments in the form of hydrates has become a safe and efficient method. If sulfur dioxide (SO2), one of the flue gas impurities, is also sequestered, the cost of CO2 purification and sequestration can be effectively reduced. However, there is a lack of in-situ observation of how SO2 affects the nucleation and growth process of CO2 hydrates. In this study, a visual microfluidic chip combined with in-situ Raman spectroscopy was used for the first time to investigate the impact mechanism of SO2 on the nucleation and growth kinetics of CO2 hydrates in porous media. The results indicate that SO2 could promote the nucleation and growth of CO2 hydrate in the following aspects: First, the diffusion of SO2 in solution induces spontaneous convection of the solution in the pores, which could promote the nucleation of mixed hydrates. After nucleation, dissolved SO2 acts as a “seed” for hydrate formation, and the pore solution is covered with hydrate microcrystals, providing heterogeneous nucleation sites for hydrate growth in solution. During the growth stage, SO2 could induce the preferential growth of mixed hydrates within the solution and enhance the growth rate of hydrates, acting as a promoter of hydrate formation. As CO2-SO2 mixed hydrates preferentially grow in solution and grow denser, it could quickly cement the pores, which could significantly improve the stability of the reservoir and form a strong hydrate barrier in the reservoir. These findings have important theoretical value and guiding significance for the synchronous sequestration of CO2-SO2 by hydrates.