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根据天然气组分组成及碳、氢同位素特征,分析了吐哈盆地台北凹陷天然气的地球化学特征、成因及来源。研究区烃类气体以甲烷为主,主要分布在60%～80%之间,重烃气(C2+)含量较高,集中在20%～40%之间,天然气干燥系数(C1/C1-5)变化较大,集中在60%～80%之间,为典型的湿气;非烃气体总体含量低,主要为N2和CO2,其中雁木西地区较高含量的N2主要来源于大气氮。天然气δ13 C1值偏低,集中在-41‰～-39‰之间,δ13C2值大于-29‰,主频率为-28‰～-26‰,δ13 C3值、δ13 nC4值集中在-26‰～-24‰之间,表明台北凹陷天然气主要为煤成气。天然气δD1值分布在-239.6‰～-111.8‰之间,主频率为-240‰～-230‰,表明研究区气源母质主要形成于陆相淡水沉积环境,且天然气成熟度不高。雁木西油田部分样品天然气湿度较大且碳、氢同位素发生倒转,主要是生物降解作用所致。天然气主要处于未熟—低熟阶段(RO≤0.8%),气源对比表明,台北凹陷天然气主要来源于中侏罗统西山窑组未熟—低熟烃源岩,其次为下侏罗统八道湾组成熟烃源岩。
Based on the composition of natural gas and the characteristics of carbon and hydrogen isotopes, the geochemical characteristics, origin and origin of natural gas in the Taibei Sag of the Turpan-Hami Basin are analyzed. Hydrocarbon gas in the study area is mainly methane, mainly distributed between 60% and 80%, and heavy hydrocarbon gas (C2 +) content is high, concentrated between 20% and 40%. Natural gas drying coefficient (C1 / C1-5 ), Which are concentrated in the range of 60% -80%, are typical moisture. The non-hydrocarbon gases are mainly low in total content, mainly N2 and CO2, of which the higher content of N2 in Yanmuxi region mainly comes from atmospheric nitrogen. Δ13C2 value is greater than -29 ‰, main frequency is -28 ‰ -26 ‰, δ13C3 value and δ13 nC4 value are concentrated in the range of -26 ‰ ~ -24 ‰, indicating that the natural gas in Taipei depression is mainly coal-derived gas. The δD1 values of natural gas ranged from -239.6 ‰ to -111.8 ‰, and the dominant frequencies ranged from -240 ‰ to -230 ‰, indicating that the gas source parent material in the study area mainly formed in the continental fresh water depositional environment and the natural gas maturity was not high. Some samples of the Yanmuxi Oilfield have high natural gas humidity and reverse carbon and hydrogen isotopes, mainly due to biodegradation. Natural gas is mainly in the immature - low maturity stage (RO≤0.8%). Comparison of gas sources shows that the natural gas in the Taipei sag mainly comes from the immature - low maturization source rocks of the Xishayao Formation in the Middle Jurassic, followed by the Badaowan Formation of the Lower Jurassic Mature source rocks.