依据10余口探井60多个气样的化学成分和碳同位素组成数据，并结合烃源岩和储层沥青资料，研究了四川盆地东北部宣汉—达县地区普光气田的天然气地球化学特征、成因及来源，结果表明：普光气田飞仙关组、长兴组天然气为高含硫化氢的干气，其化学成分表现出古油藏原油裂解气的特点;普光气田的烃类气以甲烷为主，干燥系数基本上都在0.99以上，富含非烃气体（CO₂和H₂S平均含量分别达5.32%和11.95%）；普光气田天然气甲烷碳同位素较重，在－29‰~－34‰之间（表征其高热演化性质），乙烷δ¹³C值主要在－28‰~－33‰之间（表征其属油型气）；普光气田天然气与邻近的川东北其他气田的同层位天然气具有同源性，而与石炭系气藏天然气在化学成分、碳同位素组成上有所不同，意味着各有不同的气源；普光气田储层沥青在生物标志化合物组合和碳同位素组成上反映出其与上二叠统龙潭组泥质烃源岩具有良好的生源关系；天然气乙烷碳同位素与各层系烃源岩干酪根碳同位素值对比结果揭示普光气田天然气主要来自二叠系烃源层。

Based on the molecular and stable carbon isotope compositions of over 60 gas samples collected from more than 10 exploration wells, in combination with the analytical data of source rocks and reservoir bitumen, the geochemical characteristics and origin of gases from the Puguang gas trap and other gas traps in Xuanhan-Daxian region of the eastern Sichuan Basin have been investigated. Results indicate that the natural gases in the Feixianguan and Changxing reservoirs of the traps belong to dry gas with high amounts of H₂S, and show a molecular composition feature of the gas cracked from oil in the traps. The gases are dominated by methane with dryness index mostly more than 0.99, and contain abundant non-hydrocarbon components with CO₂ and H₂S being 5.32% and 11.95%, respectively. The methane is isotopically heavy (－29‰~－33‰ ), suggesting a high level of thermal maturity, and the δ¹³C values for ethane range mainly from －28‰ to －33‰ indicative of sapropelic organic source. The studied gases are believed to have a common source with the gases from the same reservoir age strata in the adjacent gas fields of the eastern Sichuan basin, but different in origin from Carboniferous gases due to different molecular and carbon isotope compositions. The compositions of biomarkers and carbon isotopes indicate a genetic relationship between the reservoir bitumen and the source rock in upper Permian Longtan Formation. The carbon isotope correlation between ethane in the natural gases and source rock kerogens shows that the gases in the reservoirs were mainly derived from Permian strata.