东濮凹陷北部盐湖相原油特征与成因

Characteristics and Formation Mechanism for the Saline Lacustrine Oil from the North Dongpu Sag

东濮凹陷盐湖相油气成因与成藏机理研究薄弱。采用色谱/质谱(GC/MS)等常规技术,结合傅立叶变换离子回旋共振质谱、单体烃碳同位素技术,对东濮凹陷北部文明寨、卫城地区油气特征及其成因进行了解剖。结果表明,该区原油具有植烷对姥鲛烷优势显著、伽马蜡烷富集、升藿烷"翘尾"、甾烷异构化程度较低等咸水、盐湖相原油的典型特征。原油还具有正构烷烃单体烃碳同位素呈低碳重、高碳轻、近两段式分布的特征,与柴达木盐湖相原油有所差异。原油中检测到丰富的S_1、S_2、O_1S_1、N_1、O1、O_2、O_3等芳构化程度较低的NSO化合物,其与该区低熟油的形成关系密切。油-油、油-岩详细对比表明,东濮凹陷北部原油主要来自埋深超过3 000 m的沙三—沙四段烃源岩、存在不同成熟度原油混合聚集现象。研究结果对该区进一步油气勘探具有重要指示意义。

Conventional geochemical methods including GC/MS, Rockeval combined with ESI FTICR MS and compound specific carbon isotopic analysis are used to reveal hydrocarbons generation and migration style for the saline lacustrine oils from the Wenmingzhai and Weicheng Oilfield in the North Dongpu Sag, Bohai Bay Basin, which is still unclear enough up to date. It was observed that the crude oils bearing typical characteristics of saline lacustrine oils such as predominance of phytane to pristine and C35hopane to C34hopane, enrichment of gammacerane, and low extent of isomerization of steranes. The oils are also featured by twostage carbon isotope distribution of nalkanes：the δ13C for the nalkanes with carbon number less than 21 is ranged in -29‰ to -28‰, while those larger than 21 is ranged in -31‰ to -29‰, which is different from “parallel lines pattern” for the saline lacustrine oils from the Western Qaidam Basin, suggesting different paleoenvironment and precursors for the nalkanes in the North Dongpu Sag. Abundant NSOs compounds including S1,S2,O1S1,N1,O1,O2 and O3 with low extent of aromatization are detected from the oils analyzed, which were predicted having a close genetic relationship with the immature oils in the area. A detailed oiloil and oilsource rock correlations showed that the crude oils analyzed are primarily derived from Es3 and Es4 source rocks with burial depth larger than 3 000 m. It was suggested that the crude oils are mixed by different source rocks with varied thermal maturity, which would be instructive for the further petroleum exploration in the area.