Gas-source correlation is generally focused on the genetic type of the main gas components, dominantly oil-associated gas or coal-derived gas. Gases from the Yuanba and Tongnanba gas reservoirs are dominated by methane with an average content of 95.36%. The average contents of ethane, propane, butane are 1.60%, 0.29%and 0.09%, respectively. In general, for the Yuanba and Tongnanba gas reservoirs, alkane gas has an average content of 97.34%, and CO2 has an average content of 0.63%, which only accounts for 6.5‰of the methane. According to the discrimination criteria thatδ13C2 value is greater than–28‰for coal-derived gas and lower than–28.5‰for the oil-associated gas, Yin et al. suggested that the gases from the Yuanba gas reservoir be a mixture of coal-derived and oil-associated gases, and the gases from the Tongnanba gas reservoir be oil-associated gas. However, the discrimination criteria of δ13C2 for coal-derived and oil-associated gases are only valid when the alkane gases have not undergone secondary alteration and have positive carbon isotopic series among C1-C4 alkanes. Hence, it is concluded that gases from the Yuanba and Tongnanba gas reservoirs are coal-derived gases due to their high content and heavy carbon isotopic values of methane (–31.3‰), which is typical for high mature coal-derived gases in the world. Though Yin et al. suggested that abiogenic CO2 of these two reservoirs is originated from metamorphism or hydrolysis of deep carbonate rocks, we proposed that these CO2 gases be self-generated and self-accumulated under the corrosion of calcarenaceous sandstone of the Triassic Xujiahe Formation.% 气藏的气源系指其中主要组分气的成因类型，通常为油型气或煤成气.元坝和通南巴气藏主要组分甲烷平均含量为95.36%，乙烷、丙烷和丁烷平均含量分别为1.60%、0.29%和0.09%，烷烃气总平均含量为97.34%，而 CO2平均含量仅0.63%，为甲烷的6.5‰.印峰等文中仅应用δ13C2值大于−28.0‰为煤成气、小于−28.5‰为油型气指标，鉴定认为元坝气藏是煤成气和油型气的混合改造型气、通南巴气藏主要为油型气.该两气藏主要组分甲烷的碳同位素组成δ13C1平均值为−31.3‰，具有世界高成熟煤成气δ13C1特征，因此认为该两气藏气源主要是煤成气，利用δ13C2值鉴别煤成气或油型气时，只有烷烃气具正碳同位素系列方才适用，在碳同位素发生倒转或异常的负碳同位素系列情况下往往不适用.印峰等文中认为两个气藏无机成因 CO2为深部碳酸盐岩变质或水解成因，作者则认为CO2是须家河组钙屑砂岩经有机酸溶蚀自生自储成因.图1表5参29
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