东营凹陷南坡高蜡油成因及其油源研究

Origin and hydrocarbon source of high wax content oils in southern slope zone of the Dongying Depression

随着油气勘探逐渐扩展至深部层系,东营凹陷南坡古近系孔店组和奥陶系潜山相继发现多口高蜡油流井,原油普遍具有较低的含硫量和密度,与古近系沙河街组原油物性具有明显差异。东营凹陷南坡高蜡油的成因及来源存在诸多争议,严重制约了深层油气的勘探,受到广泛关注。本文通过全二维色谱–飞行时间质谱和沸腾包裹体分析,结合单体烃碳同位素和生物标志化合物分析,对东营凹陷南坡高蜡油和深部烃源岩进行了综合评价。结果表明:东营凹陷南坡孔店组高蜡油和奥陶系原油具有相同的来源,二者都具有低含量重排锥满烷、高含量金刚烷和低甲基菲比值等特征,表明它们是多期充注混合的原油;沸腾包裹体具有液相、气相和盐水包裹体共存且同时包裹的特征,储层中流体以混相运移为主;高蜡油与沙河街组四段烃源岩具有亲缘关系,沙四段烃源岩中高等植物和细菌是原油高蜡质形成的物质基础,深部气侵是高蜡物质聚集的重要因素。东营凹陷南坡高蜡油成因与来源研究,对揭示该地区深部油气藏的形成机制及深部油气资源评价具有重要意义,也对其他地区的高蜡油研究具有较好的借鉴意义。

With the ever-increasing exploration of oil and gas, exploration for energy resources has inevitably extended into deeper layers. A suite of oils from the Kongdian Formation and Ordovician buried hill in the south slope of the Dongying Depression has recently been discovered. These oils are characterized as having a high content of waxy alkanes, low concentration of sulfur compounds, and low density, which differ from the overlying Tertiary oils of the Shahejie Formation. The origin and source of these wax oils which restricted the exploration have attracted much attention. In this study, the high wax crude oils and deep source rocks were characterized via GC×GC-TOFMS, fluid inclusion analysis, monomer hydrocarbon isotope analysis, and absolute content of biomarkers analysis. Stable carbon isotopic values of different components of the high wax oils indicate that these oils from the Kongdian Formation and Ordovician are from the same source. As the oils have higher adamantane content, lower rearranged drimanes content, and alkylphenanthrene index, we confirmed that these oils are a secondary hydrocarbon accumulation from the mixing of an early formed oil and a late formed gas. Based on the coexistence of liquid, gas, and brine inclusions, we recognize that the heterogeneous migration occurred in the deep reservoir. Combining the isotope and sedimentary analysis results, we speculated that these oils of the Kongdian and Ordovician bear typical features of deep Es4 source rocks. Maturity, biomarker, isotope, and inclusion analyses validated that the southern slope zone of the Dongying Depression experienced gas invasion, and it is suggested that the higher plants and bacteria of the source rocks and gas invasion in geological history are responsible for the formation of the high waxy oils. This study helps to unravel hydrocarbons accumulation mechanisms and deep petroleum resources evaluation in this area, which can also be applied to other basins to investigate high wax oil reservoirs.