Formation and dissociation of CO2 hydrates in porous media in the presence of clay suspensions

Abstract

CO2 storage in marine sediments in the form of solid hydrates with high storage capacity and stability is a promising approach for the control of greenhouse gas pollution. Specifically, clay is much abundant in marine minerals, and multiple forces exist between fine clay particles suspended in seawater, significantly affecting the hydrate formation and dissociation behavior. This study investigates the phase transition performance of CO2 hydrates with or without montmorillonite and illite particles using low-field nuclear magnetic resonance. According to the DLVO theory, the total interaction potential between the montmorillonite particles reached 358 kbT, with that between illite particles being only 43 kbT. It was found that water in large pores was preferentially consumed during hydrate formation, with clay particles significantly promoting the conversion of water into hydrate. In seawater-montmorillonite and seawater-illite solutions, a higher number of water molecules was detected in the small and medium pores, respectively. Notably, the initial pore structure changed upon hydrate dissociation, with more medium pores formed. This effect was enhanced in the seawater-montmorillonite solutions and weakened in seawater-illite solutions. The findings could further clarify the formation and dissociation kinetics of CO2 hydrates in the presence of clay particles, as well as the geological structure evolution and safety of CO2 hydrate storage under the seafloor.