二连盆地下白垩统烃源岩特征及其对油气分布的影响

 二连盆地石油与天然气勘探始于1955 年,目前已发现了扎布油田、吉格森油田等十余个油田,但是二连盆地的勘探也存在着地质情况复杂、勘探难度大、探明程度低等问题。已有研究表明,虽然50 余个凹陷都自成一个独立的沉积单元,有相似的烃类生成、运移和聚集特征。但是每个凹陷,甚至是同一凹陷中不同的洼槽,它们烃源岩的展布、烃源岩地球化学特征差别很大。分析了二连盆地20 余个凹陷、30 余口探井下白垩统烃源岩资料,总结烃源岩的展布、烃源岩地球化学特征,对比它们的差异性以及对油气分布的影响。结果表明,二连盆地下白垩统烃源岩对油气产出情况和油气分布有着很大的影响,暗色泥岩累计厚度大、有机质丰度基本达中等以上、有机质类型更偏腐泥型-I型或II1型、埋深大于该凹陷生油门限深度的凹陷油气产出情况更好。阿尔善组烃源岩对油源的贡献比腾格尔组更大,阿尔善组烃源岩对油气的分布影响程度更大。

Characteristics of Lower Cretaceous Source Rock and Its Effects on Hydrocarbon Distribution in Erlian Basin

The oil and gas exploration of Erlian Basin began in 1955, and now more than 10 oilfields have been found, such as Zhabu oilfield, Jigesen oilfield. But, difficulties exist in the exploration of Erlian Basin, due to, for example, the complex of deposit geology and the low level of proven deposits. The previous studies show that there are 50 sags with an independent sedimentary unit of their own, and with their own similar characteristics of hydrocarbon generation, migration and accumulation. But as a matter of fact, even in different subsags of the same sag, the distribution of hydrocarbon source rock and geochemistry characteristics of hydrocarbon source rock are different. This paper analyzes the data of more than 20 sags in Erlian Basin and the Lower Cretaceous hydrocarbon source rocks of more than 30 wells. And then, some common features of distribution and the geochemical characteristics of hydrocarbon source rocks are revealed, and their differences and the effects on the distribution of oil and gas are compared. It is shown that the geochemical characteristics of Lower Cretaceous source rocks have a great influence on the production and distribution of oil and gas in Erlian Basin. Therefore, for the sags with thick dark mudstone, the abundance of organic matter is basically above the medium, the organic matter type is more partial sapropel (type I or II₁), and the dark mudstone is buried deeper than its oil generation threshold depth, and is more conducive to oil and gas output. The contribution of the source rocks of Aershan group to the reservoir is bigger than that of Tenggeer group, so the source rocks of Aershan group have a bigger influence on the distribution of oil and gas.