内蒙古西部额济纳旗地区X井油气显示特征与油气源探讨

Discussion on characteristics of hydrocarbon shows and hydrocarbon source of X well in Ejina Banner region,western Inner Mongolia,China

根据内蒙古额济纳旗地区X井白垩系额济纳旗组、侏罗系麻木乌苏组、古生界顶面风化壳等不同层段的油气显示特征和钻井泥浆烃类气体组分、甲烷C同位素的分析结果,认为侏罗系和白垩系油气显示特征相同,为油与气显示,气体样品的干燥系数(C1/C总)为0.80～0.87,甲烷C同位素δ13C1为-48.19‰～-50.87‰,表现了低成熟热解气的特征;古生界风化壳为气显示,天然气干燥系数(C1/C总)为0.91～0.92,甲烷C同位素δ13C1为-21.56‰～-30.91‰,表现了高成熟热解气的特征。该井及邻区的中生界、古生界烃源岩干酪根类型及其演化程度具有显著的差别,中生界烃源岩以低成熟混合型干酪根为主,古生界烃源岩为成熟—高成熟(或过成熟)的混合型-腐泥型干酪根。表明该区存在以中生界侏罗系—白垩系低成熟烃源岩为油气源的油气系统和古生界高成熟(或过成熟)烃源岩为气源的油气系统,指示了古生界油气资源前景。

Through analyzing the hydrocarbon shows statistics, gas components of drilling mud and methane carbon isotope of different Formations, including Cretaceous Ejina Banner Formation, Jurassic Mamuwnsu Formation and Paleoz0ic superface weathered crust of X well in Ejina Banner region, we suggest that Jurassic and Cretaceous have the same hydrocarbon shows statistics, namely oil and gas shows, and the dry coefficient of gas samples ranging 0.80-0.87, the average methane carbon isotope （δ^13C1） ranging -48.19‰-50.87‰, which show that the gas has and the characteristics of low mature pyrolysis gas. Palaeozoic weathering crust is gas shows, with the dry coefficient ranging 0.91-0.92, and the average methane carbon isotope （δ^13C1） is -21.56‰, indicating that the gas has the characteristics of high mature pyrolysis gas. The kerogen types and evolution degree are remarkable different between Mesozoic and Palaeozoic sources rocks of X well and its vicinity. Mesozoic sources rocks are low mature mixed kerogen, and Palaeozoic sources rocks are maturehigh mature （over mature） mixed-sapropehc kerogen. It shows that there are petroleum system of Mesozic Jurassic-Cretaceons low mature source rocks as hydrocarbon source and Palaeozoic high mature source rocks as hydrocarbon source, which indicate the hydrocarbon prospects of Palaeozoic.