银额盆地吉格达凹陷原油地球化学特征及其意义

Geochemical Characteristics of Crude Oil in Jigeda Sag of Yingen-Ejin Basin and Its Significances

银额盆地石炭系—二叠系油源存在争议,在一定程度上制约了该区的油气勘探进程。通过对居延海坳陷吉格达凹陷蒙额参3井原油物理性质、地球化学特征的研究,以期明确原油的成因及来源,为油气勘探提供依据。研究结果表明,蒙额参3井华力西期侵入岩和二叠系白云质砂岩中的原油物理性质基本一致,为低密度低硫中质正常原油,原油族组成具有高饱和烃、低非烃和沥青质以及高饱芳比的特征,且下部原油饱芳比远高于上部原油。吉格达凹陷华力西期侵入岩与二叠系砂岩原油饱和烃气相色谱特征、C同位素及生物标志化合物特征共性与差异同在,指示生烃母质均来源于盐度较高的海相还原环境,以浮游植物为主;二叠系原油陆生高等植物的贡献较大。油源对比表明,蒙额参3井华力西期侵入岩和二叠系砂岩原油均与白垩系巴音戈壁组烃源岩生物标志化合物特征差异明显,与石炭系—二叠系烃源岩具有良好的亲缘关系。其中,二叠系原油与二叠系烃源岩具有较好亲缘关系,华力西期侵入岩原油与干泉组上段烃源岩关系更密切。石炭系—二叠系油源的发现拓展了银额盆地油气勘探新层系,对北方古生界油气勘探具有很好的指导作用。

There is a dispute on the oil–source of Carboniferous and Permian system in Yingen–Ejin basin,which restricts the process of oil and gas exploration in this area to a certain extent.In order to clarify the oil origin and source and provide basis for oil&gas exploration in this area,research of the basic physical properties and geochemical characteristics of the crude oil from well Mengecan 3 in Jigeda Sag of Juyanhai depression was conducted.The results show that the physical properties of the crude oil in the Variscan intrusive rocks are basi-cally the same as those in the dolomite sandstones of the Permian system for well Mengecan 3.The oil is low-density,low-sulfur and normal medium crude oil,composition of which is characterized as high saturated hydrocarbon content,low non-hydrocarbon and asphaltenes content,and high ratio of saturated to aromatic hy-drocarbons,and the saturated to aromatic hydrocarbons ratio of the lower crude oil is much higher than that of the upper crude oil.The gas chromatography characteristics of saturated hydrocarbon,carbon isotope character-istics and biomarkers of the crude oil in the Variscan intrusive rocks and Permian sandstones of Jigeda Sag have both similarities and differences,As the aforementioned,the results indicate that the parent materials of hydro-carbon were derived from reducing and high paleo-salinity conditions in the marine,and phytoplankton was the main source,while the proportion of terrestrial higher plants is higher for the oil source in Permian sandstone.Oil source comparison shows that the characteristics of biomarkers of Variscan intrusive rocks and Permian sandstone crude oil in well Mengecan 3 are significantly different from those of cretaceous Bayingebi formation,and it is closely related to the Carboniferous-Permian source rocks.The crude oil from Permian sandstones show favorable correlations with the Permian source rocks,while the crude oil from Variscan intrusive rocks show more closely correlations with the source rock of upper Ganquan formation.The discovery of Carbonifer-ous Permian oil source has expanded the new series of oil and gas exploration in Yingen-Ejin basin,and has a good guiding role in oil and gas exploration of Paleozoic in North China.