Structure and composition of gas hydrate in sediment recovered from the JAPEX/JNOC/GSC et al. Mallik 5L-38 gas hydrate production research well, determined by X-ray diffraction and Raman and solid-state nuclear magnetic resonance spectroscopy

Abstract

Gas hydrate in core samples recovered from depths between 898 and 1107 m in the JAPEX/JNOC/GSC et al.Mallik 5L-38 gas hydrate production research well was characterized using powder X-ray diffraction (PXRD), Raman spectroscopy, and solid-state nuclear magnetic resonance (NMR) spectroscopy. The PXRD results show that the gas hydrate present is Structure I (sI), with typical lattice constants of 1.186 to 1.188 nm (at 100K). The 13CNMR spectra, obtained at 173K, show the characteristic sI hydrate pattern for methane distributed over the two sI hydrate cages.Variable line widths reflect the mineral content. The Raman spectra also reflect the presence of methane encaged in the two sI hydrate cages. The occupancy ratios for methane in the small and large cages, derived from the NMR and Raman spectra, were used to estimate hydration numbers according to the solid-solution theory of van der Waals and Platteeuw. Hydration numbers range from 6.1 to 6.3, in good agreement with those determined for pure gas hydrate.