本文關鍵詞： 天然氣 稀有氣體 氬同位素 元壩氣藏 氣源對比　出處：《天然氣地球科學》2017年07期 　論文類型：期刊論文

【摘要】：天然氣稀有氣體同位素研究作為一個有別于烴類地球化學的新體系,在進入油氣地質、地球化學研究領域僅20余年的時間里已取得了長足進展。元壩氣田是繼發(fā)現國內最大的海相氣田——普光氣田之后,在四川盆地內發(fā)現的又一個大型海相氣田。元壩氣田天然氣烴源問題一直存在爭議,主要原因是天然氣地球化學數據揭示為源巖高—過演化階段產物,而元壩氣田能夠供氣的主要烴源層系均為高—過演化階段,形成了對烴源認識的差異。研究共分析元壩氣田天然氣樣品19個,組分分析結果表明干燥系數分布于0.98~1之間,甲烷和乙烷碳同位素組成分別為-35.6‰~-28.3‰、-34.6‰~-21.62‰;稀有氣體同位素組成~3He/~4He值為(2.50~0.70)×10~(-8),~(40)Ar/~(36)Ar值為340.7~861.92,主頻分布在340.7~500之間。天然氣為高成熟—過成熟階段的產物。研究認為,在元壩氣田天然氣有機地球化學數據展示多解而無法確定烴源層系的前提下,元壩氣田天然氣氬同位素特征所表征的源巖定年與發(fā)育的烴源巖不符,但又能揭示一些有意義的信息。元壩氣藏烴源可能是震旦系或下寒武統(tǒng)筇竹寺組,燕山期早期熱演化形成古油藏后,在地質歷史變遷中遭到改造或破壞,于燕山中期又經歷古油藏持續(xù)埋深,經歷化學改造和流體調整,原油(或分散有機質)裂解生成天然氣,再經過喜馬拉雅期的調整改造在構造—巖性復合圈閉富集形成現今的天然氣藏。原油裂解天然氣中氬同位素特征表征的是古油藏裂解天然氣的氬同位素特征和上三疊統(tǒng)須家河組高—過成熟的腐殖型烴源巖形成的天然氣氬同位素特征的混源。
[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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