Gas Generation from Coal and Coal-Measure Mudstone Source Rocks of the Xujiahe Formation in the Western Sichuan Depression, Sichuan Basin

The Triassic and Jurassic tight sandstone gas in the western Sichuan depression, Sichuan Basin has attracted much attention in recent years, and the Upper Triassic coal-bearing Xujiahe Formation is believed to be the major source rock. However, there are relatively few studies on the carbon isotopic heterogeneity of methane generated from coal-measure source rocks and the origin of the natural gases in Xinchang Gas Field is still controversial. In this study, one coal-measure mudstone sample and one coal sample of the Xujiahe Formation in western Sichuan Basin were selected for gold tube pyrolysis experiment to determine their gas generation characteristics. Geological extrapolation of gas generation and methane carbon isotope fractionation parameters reveals that the main gas generation stage of Xujiahe Formation ranges from Late Jurassic to Cretaceous in the Xinchang Gas Field. The natural gas in the 5th member of Xujiahe Formation in Xinchang Gas Field is mainly derived from the 5th member of Xujiahe Formation itself, i.e., self-generation and self-reservoir, however, the gas in the Jurassic gas pools is mainly derived from the source rocks of the 3rd member of Xujiahe Formation rather than the 5th member of Xujiahe Formation.