百色盆地原油成因类型及聚集特征

Genetic type and accumulation characteristics of crude oil in Baise Basin

根据原油样品生物标志物和碳同位素组成的系统分析资料,揭示了指示其生源和沉积环境的地球化学参数的分布与变化规律,将百色盆地已发现的原油划分成4种成因类型。各类原油的正构烷烃碳数分布曲线、甾烷碳数分布、Pr/Ph值和碳同位素组成等指标有明显差异,在盆地内呈区域性分布。盆地东部坳陷原油成熟度总体分布格局是:东高西低,坳陷内部低边缘高。这主要是受控于生油层成烃演化与断裂活动期的时空配置关系。原油与生油层的地球化学参数在区域上分布相一致,表明原油成藏具有近源聚集的特点。这可能与盆地缺乏广覆性的疏导层和断层的切割、封堵作用有关。同时,也正是这种因素使得生油层平面上的非均质性表现为区域上原油类型的多样性。

On the basis of the systematic analytical data of biomarker and stable carbon isotopic composition of oil samples collected from Baise Basin, the distribution and variation of the geochemical indicators for original organic source and depositional environment were revealed. The genesis of oils found in Baise Basin was classified into four types. All oil subsets have obvious differences in carbon number distribution curves of n-alkane, sterane composition, Pr-to-Ph ratio and carbon isotopic ratio and also exhibit a regular distribution geographically. The maturities of oils in the eastern depression of this basin show an increasing trend on the whole from west to east and from depression center towards margin. The spatial and temporal relationship between hydrocarbon generation of source rock and activity episode of faults is mainly responsible for the pattern of maturity variation. The geochemical parameters such as Pr-to-Ph ratio of oils from various regions are closely consistent with those of adjacent source rock, which suggests that the reservoirs are characterized by oil accumulation mechanism in short secondary migration distance. This character could be related to the lack of regional conduit-reservoir rock and the fault＇s interception and block. Moreover, it is the above factors that made the heterogeneities of source rock to be reflected as the diversified oil types in different region.