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.