呼和湖凹陷原油地球化学特征及油源对比

呼和湖凹陷原油具有低密度、低粘度、低含蜡量和低凝固点的特点。其正烷烃碳数分布范围为nC14～nC35,主峰碳数多为nC21,奇偶优势基本消失,nC2-1/nC2＋2为0.55～1.186,为轻质油。原油姥鲛烷优势明显,且伽马蜡烷、β胡萝卜烷含量低,为淡水-沼泽环境。原油饱和烃含量高,非烃和沥青质含量低,轻重烃比值较高,C29甾烷20S/（20S＋20R）和C29甾烷αββ/（αββ＋ααα）均在0.45～0.58,C31藿烷22S/（22S＋22R）为0.58,这些特征表明该区原油属于成熟原油。油源对比研究表明,研究区原油只具有与南二段煤系烃源岩大致相同的碳同位素、甾烷及萜烷分布特征,原油来源于南二段煤系烃源岩。

Geochemical Characteristics of Crude Oil and Correlation of Oil Source in Huhehu Sag

The crude oil in Huhehu Sag is characterized as low density,low viscosity,low paraffin and low freezing point.The carbon number distribution of normal alkanes ranges from C14 to C35 with a peak at nC21.The OEP approximately equals to 1,nC-21/nC＋22 is about 0.55-1.186,sorting to light oil type.The crudeoil,with pristane prevalence and low contents of γ-and β-carrotenes,belonging to fresh water-palustrine.It has high saturated hydrocarbon content,low nonhydrocarbon and asphaltene,a bit high to heavy hydrocarbon ratio.The ratio of 20S/（20S＋20R） and αββ/（αββ＋ααα） are between 0.45 to 0.58.The ratio of 22S/（22S＋22R） is 0.58.These characteristics indicate the crude oil of Huhehu Sag belonging to mature oil.The oil-source rock correlation indicates that the crude oil has the similar carbon isotope compositions,and the similar steranes,terpanes distribution with the coal hydrocarbon source rocks of Member 2,Nantun Formation（K1n2）,suggesting that the crude oil in the study area was derived from the coal hydrocarbon source rocks of K1n2.