稀有气体同位素在四川盆地元坝气藏气源对比中的应用

发布时间：2018-02-17 00:23

  本文关键词： 天然气 稀有气体 氩同位素 元坝气藏 气源对比　出处：《天然气地球科学》2017年07期 　论文类型：期刊论文

【摘要】：天然气稀有气体同位素研究作为一个有别于烃类地球化学的新体系,在进入油气地质、地球化学研究领域仅20余年的时间里已取得了长足进展。元坝气田是继发现国内最大的海相气田——普光气田之后,在四川盆地内发现的又一个大型海相气田。元坝气田天然气烃源问题一直存在争议,主要原因是天然气地球化学数据揭示为源岩高—过演化阶段产物,而元坝气田能够供气的主要烃源层系均为高—过演化阶段,形成了对烃源认识的差异。研究共分析元坝气田天然气样品19个,组分分析结果表明干燥系数分布于0.98~1之间,甲烷和乙烷碳同位素组成分别为-35.6‰~-28.3‰、-34.6‰~-21.62‰;稀有气体同位素组成~3He/~4He值为(2.50~0.70)×10~(-8),~(40)Ar/~(36)Ar值为340.7~861.92,主频分布在340.7~500之间。天然气为高成熟—过成熟阶段的产物。研究认为,在元坝气田天然气有机地球化学数据展示多解而无法确定烃源层系的前提下,元坝气田天然气氩同位素特征所表征的源岩定年与发育的烃源岩不符,但又能揭示一些有意义的信息。元坝气藏烃源可能是震旦系或下寒武统筇竹寺组,燕山期早期热演化形成古油藏后,在地质历史变迁中遭到改造或破坏,于燕山中期又经历古油藏持续埋深,经历化学改造和流体调整,原油(或分散有机质)裂解生成天然气,再经过喜马拉雅期的调整改造在构造—岩性复合圈闭富集形成现今的天然气藏。原油裂解天然气中氩同位素特征表征的是古油藏裂解天然气的氩同位素特征和上三叠统须家河组高—过成熟的腐殖型烃源岩形成的天然气氩同位素特征的混源。
[Abstract]:As a new system different from hydrocarbon geochemistry, the isotopic study of natural gas rare gases is entering oil and gas geology. Great progress has been made in the field of geochemical research in the past 20 years. Yuanba gas field is the largest marine gas field in China-Puguang gas field. Another large marine gas field was discovered in Sichuan Basin. The source of natural gas in Yuanba gas field has always been controversial, mainly because the geochemical data of natural gas was revealed as the product of high-over-evolution stage of source rock. However, the main hydrocarbon source layers that can supply gas in Yuanba gas field are all in the high-over-evolution stage, which has formed the difference of understanding of hydrocarbon source. 19 samples of natural gas from Yuanba gas field were studied and analyzed. The results of composition analysis show that the drying coefficient is between 0.98 ~ 1. The carbon isotopic compositions of methane and ethane are -35.6 鈥，

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