Hydrocarbon gas composition and origin of core gas from the gas hydrate reservoir in Qilian Mountain permafrost

Hydrocarbon gas composition and carbon isotope of core gas from the hydrate reservoir in DK-2 hole, one of the scientific drilling holes of gas hydrate in Qilian Mountain permafrost, were determined and analyzed. The results indicate that gas hydrate from Qilian Mountain permafrost has complex hydrocarbon gas composition, with relatively high ethane and propane besides the dominant methane. All the δ13C1 values are higher than -50‰, and molecular ratios (R) are generally lower than 100, obviously suggesting thermogenic gas characteristics. According to the geological background and lithologic characteristics of the drilling area, the authors preliminarily estimate that gas comes from the near-by highly matured or over-matured coal-related gas and the deeper thermogenic gas which has migrated upward from the depth.