川西北地区双鱼石气藏中二叠统天然气碳氢同位素特征及气源探讨

天然气碳氢同位素组成、烃源岩和储层沥青生物标志化合物是天然气成因鉴别和气源对比研究最主要、最有效的方法。目前关于川西北双鱼石地区中二叠统天然气成因和来源研究较少。根据最新钻井成果和野外资料，应用天然气组分、组分碳氢同位素数据，结合不同层系烃源岩和储层沥青生物标志化合物对比分析，对川西北地区中二叠统天然气来源进行了判识，结果表明：①川西北地区双鱼石气藏中二叠统天然气均为干气，CH₄含量高，平均为96.28%，C₂H₆含量低，平均为0.11%，C₃H₈、C₄H₁₀几乎没有，H₂S含量低，平均为0.32%；②双鱼石气藏天然气甲烷碳同位素值分布较为集中，介于-30.5‰~-29.5‰之间，乙烷碳同位素值介于-29.9‰~-26.7‰之间，天然气成因为原油二次裂解气；③通过天然气碳氢同位素、储层沥青—烃源岩生物标志化合物对比认为，双鱼石气藏中二叠统栖霞组天然气来源为混源，主要来源于下寒武统筇竹寺组烃源岩，部分来源于中二叠统梁山组。

Carbon and hydrogen isotope characteristics and source of natural gas in Shuangyushi gas reservoir,northwestern Sichuan Basin

The carbon and hydrogen isotope composition of natural gas, and the biomarkers of source rock and reservoir asphalt are the most chief and effective method to study the origin and source of natural gas. At present, there are few studies on the origin and source of natural gas of Middle Permian in Shuangyushi gas reservoir of northwest Sichuan Basin. Therefore, based on the latest drilling results and field data, using data of natural gas components and carbon and hydrogen isotopes, combined with comparative analysis of biomarker compounds of source rocks and reservoir asphalts of different strata, the source of Middle Permian natural gas in western Sichuan is identified. The results show that: (1)The Middle Permian natural gas in Shuangyushi gas reservoir in northwest Sichuan Basin is dry gas with high methane content (96.28%) and low ethane content (0.11%). Almost no propane and butane, and low H₂S content (0.32%). (2)The carbon isotopic distribution of methane in Shuangyushi gas reservoir is relatively concentrated, between -30.5‰ and -29.5‰. The carbon isotopic distribution of ethane is between -29.9‰ and -26.7‰. The natural gas in Shuangyushi gas reservoir is secondary cracking gas of crude oil. (3)Through the contrast of carbon and hydrogen isotope and biomarkers of reservoir asphalt and source rock, it is found that the natural gas of Middle Permian Qixia Formation in Shuangyushi gas reservoir mainly comes from the source rock of Lower Cambrian Qiongzhusi Formation, part of it comes from Middle Permian Liangshan Formation.