The Sulige Gas Field is a giant litholitic gas reservoir in the Upper Palaeozoic strata in the Ordos Basin. The determinations of gas chromatography indicates a kind of humid gas with lower dryness and dominant methane. The carbon isotopes in n-alkane exhibit a trend of δ13C1＜δ13C3＜δ13C2＜δ13C4. There is a positive correlation between the carbon isotopes and methane contents, and a negative correlation between the carbon isotopes and ethane contents. The variations in the contents of carbon isotopes show that the natural gas from the Sulige Gas Field is a kind of coal-derived gas of organic origin and contains minor amount of CO2. The Permian gas reservoirs went through the deposition and burial of the source rocks during the Carboniferous-Permian to the Middle Jurassic, formation of the gas during the Late Jurassic to the Cretaceous, and preservation and modification of the gas from the Tertiary onwards.%苏里格气田是鄂尔多斯盆地上古生界内发现的大型岩性气藏.天然气中甲烷占绝对优势,干燥系数低,为湿气.天然气的单体碳同位素具有碳数越高,同位素越重的特点,且正构烷烃碳同位素具有δ13C1 ＜δ13C3 ＜δ13C2 ＜δ13C4 的规律.甲烷碳同位素与甲烷含量呈正相关,与乙烷含量为负相关.根据天然气单体碳同位素及其含量变化,认为苏里格天然气属煤成气.天然气中含少量CO2 气,多为有机成因.苏里格气田二叠系气藏的形成与演化可划分为石炭-二叠纪至中侏罗世气源岩沉积埋藏阶段、晚侏罗世至白垩纪天然气形成阶段和第三纪至现今的保存改造阶段.
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