Phase and kinetic behavior of the mixed methane and carbon dioxide hydrates

Abstract

Large amounts of CH₄ are stored as hydrates on continental margins and permafrost regions. If the CH₄ hydrates could be converted into CO₂ hydrate, they would serve double duty as CH₄ sources and CO₂ storage sites in the deep ocean sediments. As preliminary investigations, both the phase behavior of CH₄ hydrates and kinetic behavior of 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 and NaCl on hydrate formation. These two effects inhibited hydrate nucleation and thus made the hydrate equilibrium line shift to a higher pressure region. In addition, the kinetic data of CO₂ hydrate in the mixtures containing clay and NaCl were determined at 2.0 MPa and 274.15 K. Clay mineral accelerated an initial formation rate of CO₂ hydrate by inducing nucleation as initiator, but total amount of formed CO₂, of course, decreased due to the capillary effect of clay pores. Also, the addition of NaCl in sample mixtures made both initial formation rate and total amount of CO₂ consumption decrease.