Study on Determination Method of Natural Gas Hydrates by Micro-Laser Raman Spectroscopy

Natural gas hydrates are non-stoichiometric clathrate compounds that are formed by hydrocarbon gases and water molecules under the conditions of low temperature and high pressure. Micro-laser Raman Spectroscopy is applied as an important method to measure structural parameters (e.g. hydration number, cage occupancy). Since the gas hydrate sample readily decomposes, it cannot be measured under normal temperature and pressure. In this paper, we describe a small instrument that has been designed to use Micro-laser Raman spectroscopy at low temperature and pressure for gas hydrates. Our work focuses on the synthesis, preservation and pre-treatment methods of hydrate samples and optimizing parameters of the instrument. The method was verified by repeatedly measuring hydration numbers of the same sample with RSD less than 1%. The results show that the method is accurate and reliable and can be used to identify the structure of simple hydrates. This method has been applied to measure natural gas hydrate samples recovered from the Shenhu area of the South China Sea and also Qilian mountain permafrost with satisfying results.