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对于发育多套不同成熟度烃源岩、存在多种类型原油及天然气的复杂含油气区,如何准确判断油气来源与成因一直是非常困难的事情.准噶尔盆地南缘中部地区存在正常原油、轻质油、凝析油、蜡质油和稠油,同时也发现了大量天然气,长期以来对该地区凝析油的来源与成因一直存在很大争议,而对于蜡质油与稠油的形成则几乎没有研究.本文以该地区为研究实例,探讨复杂油气区凝析油、蜡质油与稠油成因判识地质地球化学方法,揭示该地区多种类型原油并存的原因与地球化学过程.南缘中部地区40多个原油、轻质油、凝析油和稠油化学组成及其变化特征精细分析对比表明,该区凝析油以低碳数正构烷烃为主,含有丰富的环己烷、甲基环己烷等环烷烃和苯、甲苯、二甲苯等低碳数芳烃,庚烷值在19~21%,异庚烷值在1.9~2.1,甲苯/正庚烷比值在1.5~2.0之间,其烷烃的分布与高密度蜡质原油和稠油呈镜像关系.结合该区原油、凝析油油源及天然气气源对比结果认为,该区凝析油是白垩系湖相烃源岩生成的成熟原油油藏,在后期遭受了侏罗系生成的高成熟天然气气侵改造的产物,为蒸发分馏/相控运移分馏作用形成的凝析油.蜡质油是蒸发分馏/相控运移分馏作用过程的中间产物或阶段产物,稠油是蒸发/相控运移分馏作用的残留物.蒸发/相控运移分馏作用是南缘凝析油、蜡质油、稠油形成的主要成因机理,其导致油藏原油及凝析油的正庚烷、甲基环己烷、甲苯等轻烃化合物含量发生很大变化,使凝析油的甲苯/正庚烷等比值具有很大的不确定性.因此,不能依据凝析油中甲苯/正庚烷与正庚烷/甲基环己烷比值简单地套用Thompson图版判识其成因,而必须从研究区地质条件、烃源岩成烃演化与生烃历史、各种类型油气分子组成与分布特征、不同物理化学性质油气在纵向及区域上分布等方面综合分析判识凝析油的成因.
It is always very difficult to determine the source and cause of oil and gas accurately for the development of multiple sets of hydrocarbon-bearing areas of different types of crude oil and natural gas with different maturity source rocks.The central part of southern margin of Junggar Basin has normal crude oil, Oil, condensate, waxy oil and heavy oil, but also found a large number of natural gas, condensate has long been the source and cause of controversy in the region, and the formation of waxy oil and heavy oil is almost There is no research.In this paper, we take this area as an example to discuss geo-geochemical methods to identify the genesis of condensate oil, waxy oil and heavy oil in complex oil and gas fields and reveal the reasons and geochemical processes of the coexistence of various types of crude oil in the area. A comparative analysis of the chemical composition of more than 40 crude oil, light oil, condensate oil and heavy oil in the central region and their variation shows that the condensate oil in this area is dominated by low-carbon n-alkanes and is rich in cyclohexane, Cyclopentane such as methylcyclohexane, and low-carbon aromatic hydrocarbons such as benzene, toluene and xylene, having a heptane value of 19 to 21%, an isoheptane value of 1.9 to 2.1 and a toluene / n-heptane ratio of 1.5 to 2.0 Between, its alkane distribution and Density waxy crude oil and heavy oil are mirror images.Combined with the crude oil, condensate oil source and natural gas source contrast, the condensate oil in this area is a mature oil reservoir formed by Cretaceous lacustrine source rocks. Late Jurassic suffered high gas natural gas invasion and transformation of the product for the evaporation fractionation / phase controlled transport fractionation condensate formed by the role of waxy oil is the evaporation fractionation / phase controlled migration of intermediate fractionation process The heavy oil is the residue of the evaporation / phased migration fractionation.The evaporation / phased migration fractionation is the major causative mechanism of the formation of condensate oil, waxy oil and heavy oil in the southern margin, Crude oil and condensate of n-heptane, methylcyclohexane, toluene and other light hydrocarbon compounds greatly changed the content of condensate oil toluene / n-heptane ratio with great uncertainty.Therefore, can not According to the condensate oil toluene / n-heptane and n-heptane / methylcyclohexane ratio simply applied Thompson plate to identify its origin, but from the study area geological conditions, source rock hydrocarbon evolution and hydrocarbon generation history, each Types of oil and gas molecular composition and distribution characteristics, different things Physicochemical properties of hydrocarbons in the vertical and regional distribution of a comprehensive analysis to identify the causes of condensate.