鄂尔多斯盆地南部中生界原油地球化学特征及油源分析

摘要

Samples of the Mesozoic source rocks, crude oils, an d oil-bearing sands in the southern Ordos Basin were collected systematically. Gas chromatography-mass spectrometry (GC-MS) was performed on the saturated hydrocarbon fractions extracted from these samples in order to discuss their biomarker characteristics and the origin of Mesozoic crude oils. The results show that, on the basis of biomarker source parameter distribution, the Mesozoic source rocks can be divided into five types ( type A1, A2, A3, A4 and B), and crude oils can be grouped into three types (Ⅰ,ⅡandⅢ). Type I crude oils should be derived from Chang 7 oil shales (type A1) that were deposited in a reducing, deep lacustrine environment. Type II crude oils should be sourced from Chang 7 dark mudstones (type A2) laid down in a sub-reducing to reducing, deep or semi-deep lacustrine environment. Type Ⅲ crude oils should be sourced from Chang 7 dark mudstones (type A3) laid down in a sub-reducing to reducing, semi-deep lacustrine environment, but probably also be sourced from Chang 8 or Chang 9 dark mudstones. Apparently, oil shales in Chang 7, as the main source rocks in the southern Ordos Basin, contributed significantly to the crude oils in this area.%系统采集鄂尔多斯盆地南部中生界的烃源岩、原油及油砂样品，对其饱和烃和芳烃馏分进行气相色谱-质谱分析，通过对生物标志物组成特征的研究，分析和探讨中生界原油的油源。结果表明：根据8β(H)-补身烷和C3017α(H)-重排藿烷含量，鄂尔多斯盆地南部中生界原油可划分为Ⅰ，Ⅱ，Ⅲ类。第Ⅰ类原油8β(H)-补身烷含量高， C3017α(H)-重排藿烷含量低，来自深湖相沉积相带的长7油页岩（A1类），第Ⅱ类原油8β(H)-补身烷含量较高， C3017α(H)-重排藿烷含量中等，来自深湖-半深湖沉积相带的长7暗色泥岩（A2类），第Ⅲ类原油8β(H)-补身烷含量低， C3017α(H)-重排藿烷含量高，来自半深湖沉积相带的长7暗色泥岩（A3类），由于采集样品数量限制，第Ⅲ类原油不排除来自长8或长9暗色泥岩（A3类）的可能，目前发现的原油主要是第Ⅰ类，即各油层组的原油主要是由长7油页岩提供的，它是鄂多斯盆地南部中生界的主力烃源岩。