Gas Hydrate in Crystalline-Swelled Clay: The Effect of Pore Dimension on Hydrate Formation and Phase Equilibria

Understanding of gas hydrates, for example, phase equilibria, in reservoir sediments is one of the important issues in the fields of energy production and CO2 sequestration via CH4 hydrate exploitation and CO2 hydrate formation. The composition of water in clay can change their physical properties, which influences the state in which gas hydrates exist in clays. We investigated gas hydrates in crystalline-swelled Na-montmorillonite (CS-mon) having water content of <27 wt % and maintaining crystallinity of clay particles. Instead of a gas hydrate forming in the interlayer, gas is dissolved in the swelled interlayers of clay, acting as a favorable storage site for hydrophilic CO2. In addition, gas hydrates formed in CS-mon showed both inhibited and promoted phase behavior. This revealed that the clay surface can promote the formation of a hydrate structure, but confinement in nanosized space dominates the promotion effect and causes stronger inhibition than in the bulk phase. We believe that our results not only broaden the understanding of gas hydrates in confining systems and porous materials but also provide a precise explanation of the behavior of gas hydrates in clay sediment.