辽河盆地东部凹陷原油的碳同位素组成特征

通过对辽河盆地东部凹陷原油的饱和烃、芳烃的碳同位素组成特征、原油同位素类型和单体烃同位素特征进行研究 ,发现整个东部凹陷原油及其组分的碳同位素值偏重 ,指示其源岩有机质中藻类和低等水生生物的贡献较少 ;饱和烃—芳烃的碳同位素值关系揭示东部凹陷大部分原油样品与沙河街组沙三段烃源岩的特征相近 ,而南部和北部地区少数样品表现出负的碳同位素异常 ,与该区中生界源岩样品的接近 ,推测原油中可能混入了中生界来源的油气。南部地区各样品的碳同位素类型曲线和单体烃的碳同位素曲线均相似 ,揭示了两者具相同的油气来源。北部地区各原油样品的单体烃的碳同位素类型曲线间具有相似的分布特征 ,但茨榆坨地区的原油样品的碳同位素值比牛居地区的系统偏轻 ,可能是成熟度相对较低引起的 ,表明茨榆坨地区原油具有早期成藏的特征。原油的碳同位素组成特征是研究油气来源和成藏特征分析的一种重要手段。

THE CHARACTERISTICS OF CARBON ISOTOPIC COMPOSITION OF THE DONGBU DEPRESSION IN THE LIAOHE BASIN

The carbon isotopic composition of saturated and aromatic hydrocarbons, the oil isotopic curve and individual saturated hydrocarbon isotopic composition are studied in this paper. Conclusions are drawn as follows: The isotopic values of oils and their fractions are mainly positive indicates that there are less alga and aquatic organism contributed to the organic matter. In the saturated-aromatic hydrocarbon isotopic cross-plot, the values of most oil samples are approximately equal to that of source rock of Shahejie 3 Member. Whereas some samples in the northern and southern parts have more negative isotopic values and are similar to that of Mesozoic source rocks. It can be inferred that some oils that originated from Mesozoic have mixed into these samples. Both oil isotopic curve and individual hydrocarbon isotopic distribution of the southern part are quite approximate, which shows the similar hydrocarbon origin. Individual hydrocarbon isotopic values of the Ciyutuo area are systematically more negative than that of the Niuju area shows that hydrocarbon accumulated earlier in the Ciyutuo area than in the Niuju area. In a word, the analysis of carbon isotopic composition of oil is an important approach to study the hydrocarbon origin and accumulation.