Natural gas hydrate samples were firstly recovered from Shenhu Area of South China Sea (SH-GH) and Qilian mountain permafrost (QLM-GH) in China. In this paper, laser micro-Raman spectroscopy was used to investigate the two kinds of samples to reveal the structural characteristics and the gas composition of these natural gas hydrates. The results show that SH-GH is typically structure I (sI) hydrate. Methane gas is a dominant component which accounts for more than 99% of all the guest gas. The cage occupancy of methane is larger than 99% for large cages while 86% for small cages, with the hydration number of approximately 5.99 by Raman method. In comparison, QLM-GH is formed by relatively complicated gas components. Except for methane (about 70%), there are also considerable amounts of ethane, propane and butane. It is presumed preliminarily that GH-QLM is structure II (sII) hydrate based on its Raman spectrum, with the cage occupancy ratio of methane for small to large cage (θ_S/θ_L) of 26.38, which is much larger than that of GH-SH (0.87). This is mainly because the lager molecules (i.e. ethane, propane and butane) in QLM-GH preferentially occupy the large cages and thus greatly diminish methane molecules in large cages.

Key words: gas hydrate, laser micro-Raman spectrometry, Shenhu Area, qilian Mountain permafrost