Analysis method and geological significance of C₅-C₇ light hydrocarbons in natural gas hydrate in permafrost, Qilian Mountain

A sample introduction device of vacuum thermal desorption, cold on-column and zero-pressure was built for the identification of C₅-C₇ light hydrocarbons in gas hydrate. On the basis of previous Kováts index research, 27 compounds of C₅-C₇ light hydrocarbons were identified, which provided a foundation for the geochemical study on light hydrocarbons in gas hydrate in the Juhugeng mining area, Muli coal field, Qilian Mountain. Two genetic types of gas hydrate in the Muli permafrost were divided into three types, including oil-type, coal-type and mixed-type gas based on the methylcyclohexane index. The mixed-type gas predominates in the Muli permafrost, while the other two types are in the minority.