Gas hydrates are crystalline inclusion compounds that guest gas molecules (e.g. light hydrocarbons, carbon dioxide, or hydrogen) are incorporated into host lattice structure built up with hydrogen-bonded water molecules. Natural gas hydrates are accumulated under deep marine or permafrost environments, and have been expected as new natural gas resources. A crystal density of gas hydrate is important from aspects of physical property identification of natural gas hydrates or behavior prediction of fluids containing hydrate crystals. In this study, the crystal densities of the natural and artificial gas hydrates including hydrocarbons were estimated by solid-state <sup>13</sup>C NMR and powder X-ray diffraction techniques. As a natural sample, the pore-space gas hydrate sample recovered from the eastern Nankai Trough area during the 2012 JOGMEC/JAPEX Pressure coring operation was studied. As an artificial sample, the synthetic methane and butane mixed gas hydrates were used in this study. The crystal densities were estimated by the cage occupancies of guest gas molecules and lattice parameters of host lattice of the gas hydrates. The cage occupancies and lattice parameters were determined by <sup>13</sup>C NMR and powder X-ray diffraction techniques, respectively. The crystal density of the pore-space natural gas hydrates was almost the same as the massive ones in the literatures. In addition, we revealed that the lattice expansion by increasing large guest composition contributes to lower the crystal density. We performed this study as a part of a Japanese National hydrate research program (MH21, funded by METI).

Crystal density of natural and artificial gas hydrates including hydrocarbons

251st National Meeting (2016)

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