Effect of Water and Sand Content on Carbon Dioxide Hydrate Formation in the Clay Minerals

Carbon storage is an essential approach to mitigating global warming and realizing the negative emissions of greenhouse gases. A practical strategy is to immobilize CO2 in marine sediments in the form of hydrates. Clay, as one of the most significant components of marine sediments, has a critical impact on CO2 storage and hydrate formation. In this study, montmorillonite was selected as the clay mineral medium, and the effects of the water content, pressure, and clay content on CO2 storage were investigated. As the water content increased, the form of the CO2 storage transformed from clay adsorption to hydrate formation, resulting in a significant increase in the final amount of the CO2 storage. The activity of the bound water was positively correlated with the distance of water molecules from the clay surface. As the pressure increased from 2.5 to 3.5 MPa, the conversion of inner bound water to hydrate was facilitated, leading to an increase in the final amount of CO2 storage by 88.4%. Compared to pure clay minerals, the mixed clay–sand medium had an enhanced storage capacity, which increased by approximately 46.9%, attributed to the more available water for hydrate formation. Still, the rate of hydrate formation was slower due to decreased permeability resulting from mudding. The experimental results will help us to understand the pattern of hydrate formation from bound water in clay minerals and provide some theoretical basis for realizing CO2 storage in clay-bearing marine sediments.