Sample Pre-treatment Technologies for Gas Composition Analysis of Natural Gas Hydrates

Natural gas hydrate can only steadily exist at lower temperature and higher pressure, otherwise it will decompose into gas and water. Hereby, the pre-treatments (sample preservation, preparation, etc.) are very important to the accurate measurement of gas components of gas hydrate. Described in this paper are the pre-treatment technologies of gas hydrate that were studied experimentally, mainly including the optimal preservation temperature under atmospheric pressure, the optimal decomposition methods, the optimal ways of gas collecting and storing, and the removal methods of non-hydrate gases. The results indicate that the best temperature for gas hydrate storage is less than -100℃ under atmospheric pressure. The headspace method and syringe method can be widely used in hydrate-bound gases′ decomposition and collection, however, the drainage method was not suitable for hydrate samples containing CO₂. It was more beneficial to place the sample at -80℃ to remove the non-hydrate gases absorbed on the surface of the specimen. In addition, the use of a glass bottle with butyl rubber plug for storage of hydrate decomposition gases instead of aluminum-plastic air bag is preferential, and the optimum time to finish the analysis of molecular compositions is within 5 days.