鄂尔多斯盆地苏里格气田上古生界天然气地球化学及成藏特征

Geochemistry and accumulation of the Upper Palaeozoic natural gas in the Sulige Gas Field,Ordos Basin

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<1δ3C3<1δ3C2<1δ3C4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。

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 δC1 〈 δC3 〈 δC2 〈δC4. 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.