Three-phase equilibria (H-LW-V) for CO2 and NaCl solutions containing clay were measured to examine both electrolyte and capillary effect inside interlayer pores. Equilibrium line of 3 wt% NaCl and 10 wt% clay system was a little shifted to left side of 3 wt% NaCl solutions, which indicated that the injection of carbon dioxide into ocean sediments required higher pressure. CO2 hydrate formation kinetics was also attempted at 274.15 K and 30 bar. When clay minerals were added, the final consumption of CO2 decreased, but initial formation rate increased. Two-phase equilibria of CO2 hydrate and water solution eliminating gas phase particularly measured to simulate more closely actual deep sea condition. The overall results of this study would be used for estimating carbon dioxide injection depth and formation rate in sequestration process and making out solubility tendency in the deep sea.