川中川南地区须家河组天然气地球化学特征

四川盆地川中川南地区须家河组天然气组成主要以烃类气体为主，甲烷含量在80%～96％，C＋2重烃含量较高，分布在3％～18％；天然气干燥系数（C1/C1-5）以小于0.95为主，为典型的湿气，主要属于干酪根热降解气。天然气同位素组成特征是碳、氢同位素均较轻，δ13C1介于-43‰～-37‰，δ13C2介于-30‰～-24‰；δDCH4介于-190‰～-150‰，δDC2H6介于-150‰～-110‰。甲烷碳同位素值与干燥系数之间有很好的正相关关系，天然气碳同位素值明显比海相层系天然气碳同位素值轻，具有煤型气特征，表明须家河组天然气主要来源于上三叠统煤系烃源岩。

GEOCHEMICIAL CHARACTERISTICS OF NATURAL GAS OF XUJIAHE FORMATIONIN SOUTHERN AND MIDDLE SICHUAN

In view of the natural gas of Xujiahe Formation in southern and middle Sichuan Basin，it is concluded that the proportion of CH₄ is about 80%-96% in component of hydrocarbon，that of C₂^＋ is about 3%-18%，the ratio of C₁/（C_1-5） is less than 0.95，It is a typical wet gas and belongs to thermal degradation gas of kerogen.The gas isotope composition of δ¹³C₁ ranges from 43‰ to 37‰，while that of δ¹³C₂ from30‰ to 24‰，δD_CH4 ranges from 190‰ to 150‰，δD_C2H6 from 150‰ to 110‰.There is an fairly well positive correlation between δ¹³C₁ and the absolute concentration of methane.The carbon isotope value of natural gas of Xujiahe Formation is obviously lighter than that of natural gas in the marine facies strata，it is of the coal related gas feature，which shows that the natural gas comes from Upper Triassic coalbed source rocks.