Parameter Optimization and Analysis Method for Determination of Natural Gas Hydrate by Powder X-ray Diffraction

Gas hydrate is a form of non-stoichiometric clathrate compound which is produced by hydrocarbon gas molecules and water molecules at high pressure and low temperature. Usually under atmospheric pressure and room temperature, the hydrate sample is easy to decompose and thus the analysis must be carried out at low temperature. The analysis conditions of powder X-ray Diffraction for natural gas hydrate is the focus of this study. The influencing factors (i.e., increment, scan speed, cumulative number, and the temperature) were systematically studied to optimize the analytical parameters. As a result, a powder X-ray Diffraction method to measure the crystal structure of gas hydrate is proposed. This method has been used successfully to measure the crystal structure of the hydrate samples from both the laboratory and the Pearl River Mouth basin in the South China Sea. The results show that the hydrate samples have a similar cubic crystal structure. Both the gas hydrate from the Pearl River Mouth basin in the South China Sea and the synthetic methane hydrate in the laboratory belong to the type I hydrate and have unit cell parameters of 11.9309×10^-10 m and 11.9135×10^-10 m, respectively. This method can be used to obtain the structural information of gas hydrate, and will provide a technical support for further research of gas hydrate in China.