川西坳陷新场气田上三叠统须五段天然气来源及启示

新场气田是川西坳陷目前发现的规模最大的陆相气田，须五段是该区天然气勘探的重点层系之一，但有关须五段天然气成因和来源的认识存在分歧。在对新场气田不同层位天然气进行组分、稳定碳氢同位素和轻烃化合物组成进行测试分析的基础上，开展天然气成因鉴别和气源对比。地球化学特征研究表明，新场气田须五段天然气主体为湿气，δ¹³C₁值介于-40.2‰~-33.5‰之间，δ¹³C₂值介于-27.3‰~-23.6‰之间，δD₁值介于-215‰~-179‰之间，烷烃气碳氢同位素组成均为正序系列；C₇组成具有明显的甲基环己烷优势分布，C_5-7组成则以异构烷烃和环烷烃为主。新场气田须五段天然气为煤成气，与雷口坡组和须二段分别表现为油型气和混合气的特征明显不同，而侏罗系和须四段天然气尽管同样表现出煤成气特征，但其成熟度普遍高于须五段天然气。受须家河组不同层段烃源岩母质类型相似等因素影响，气—岩轻烃指纹对比不具有排他性，不适用于新场气田陆相天然气的气源精细对比。新场须五段天然气主要来自须五段自身，而侏罗系天然气则主要来自须三段、须四段烃源岩。

The source of natural gas reservoired in the 5th member of the Upper Triassic Xujiahe Formation in Xinchang Gasfield,the Western Sichuan Depression and its implication

The Xinchang Gasfield is the largest terrestrial gasfield in the Western Sichuan Depression,and the 5^th member of the Upper Triassic Xujiahe Formation(T₃x₅) is one of the important strata for natural gas exploration in this area.However,there was no consensus on the origin and source ofT₃x₅ gases.The identification of gas origin and gas-source correlation were conducted based on the measurement and analyses of chemical composition,stable carbon and hydrogen isotopes and light hydrocarbons.The study on geochemical characteristics indicated that,the gas was mainly wet with δ₁₃C₁,δ₁₃C₂ and δD₁ values being -40.2‰ to -33.5‰,-27.3‰ to -23.6‰ and -215‰ to -179‰,respectively,and the gaseous alkanes displayed positive carbon and hydrogen isotopic series,and the C₇ light hydrocarbons were dominated by methyl cyclohexane with the C_5-7 light hydrocarbons mainly consisting of isoalkanes and n-alkanes.TheT₃x₅ gas was coal-derived gas and different from oil-type gas and mixed gas reservoired in T₂l andT₃x₂,respectively.The Jurassic andT₃x₄ gas also display the characteristics of coal-derived gas with generally higher maturity.TheT₃x₅ gas in the Xinchang Gasfield was mainly derived from source rocks inT₃x₅ itself,whereas the Jurassic gas was probably derived mainly from the source rocks inT₃x₃ andT₃x₄.