Large amounts of CH4 are stored as hydrates on continental margins and permafrost regions. If the CH4hydrates could be converted into CO2 hydrate, they would serve double duty as CH4 sources and CO2 storage sites inthe deep ocean sediments. As preliminary investigations, both the phase behavior of CH4 hydrates and kinetic behaviorof CO2 hydrate were measured at versatile conditions that can simulate actual marine sediments. When measuring three-phase equilibria (H-LW-V) containing CH4 hydrate, we also closely examined pore and electrolyte effects of clay andNaCl on hydrate formation. These two effects inhibited hydrate nucleation and thus made the hydrate equilibrium lineshift to a higher pressure region. In addition, the kinetic data of CO2 hydrate in the mixtures containing clay and NaClwere determined at 2.0MPa and 274.15K. Clay mineral accelerated an initial formation rate of CO2 hydrate byinducing nucleation as initiator, but total amount of formed CO2, of course, decreased due to the capillary effect of claypores. Also, the addition of NaCl in sample mixtures made both initial formation rate and total amount of CO2 con-sumption decrease.