Abstract: Source analysis of natural gas is one of the geological challenges involving exploration decision-making.Exploration and development of the Xuejiahe Formation in eastern Sichuan Basin is relatively lagged behind and the source of natural gas there is still a mystery due to the fact of lacking basic geological study.Gas composition and isotope analyses show that the natural gas from the Xuejiahe Formation of Woxinshuang area features in low content of methane,high content of heavy hydrocarbon,and lower aridity coefficient.The carbon isotope values were measured to be δ¹³C₁<-40‰ and δ¹³C₃ > δ¹³C₂ > δ¹³C₁.The gas from the Xuejiahe Formation is continental oil-type gas or mixed gas from primary cracking of kerogen and is now at the mature and highly mature wet gas stage.The Formation in the area has well deve-loped dark mudstone.Organic geochemical analyses indicate a kerogen Ⅰ and Ⅱ dominated mudstone with high content of organic carbon and chloroform bitumen "A",indicating relatively high hydrocarbon generation potential.The organic matter of the mudstone was measured to be at the mature to highly mature wet gas stage.Gas from the Formation in the area has a maturity as same as that of source rocks.Combining this understanding with the gas composition and isotope analyses results,we suggest that the gas in the Xuejiahe Formation is mostly autogeneous gas and differs utterly from that in the underlying Carboniferous,the Maokou,the Longtan,the Changxing,the Feixianguan,the Jialinjiang and the Leikoupo Formations.

Key words: natural gas, Xujiahe Formation, Upper Triassic, Woxinshuang area, eastern Sichuan Basin