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

关键词:  苏里格气田  上古生界  地球化学特征  成藏

Key words:  Sulige Gas Field  Upper Palaeozoic strata  geochemistry  gas accumulation

摘要:

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。

Abstract:

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.