摘要:
通过对稠油进行常规物性、碳同位素和有机地球化学分析,系统阐述了查干凹陷稠油地化特征及其形成的主控因素。查干凹陷存在原生和次生两类稠油,原生稠油非烃含量高于饱和烃含量,原油族组分富集轻碳同位素,C29规则甾烷系列中以ααα构型为主,αββ构型甾烷含量低,没有重排甾烷。三环萜/五环萜值低,伽马蜡烷含量高,姥植比值低,其成烃母质沉积于高盐还原环境,多种地化参数表明原生稠油是巴音戈壁组烃源岩低熟演化阶段排烃的产物。次生稠油为油气运聚成藏之后,由于后期保存条件改变并经历次生改造作用形成的高密度、高黏度和低凝固点的原油。次生稠油埋深一般小于1200 m,主要为生物降解油,其中部分属于多期混源稠油。次生稠油正构烷烃损失严重,类异戊二烯烃不同程度遭受侵蚀,甾萜烷分布完整,表征原油达到中等降解程度。研究表明,原油稠化是多种稠化因素共同作用的结果,生物降解作用是研究区稠油形成的主要机制,查干凹陷后期的构造抬升为原油稠化提供了必要条件,活跃的水介质条件为浅层喜氧微生物活动提供了良好的氧化环境和营养物质。
Abstract:
Based on routine physical properties, carbon isotope and molecular geochemical analysis, this paper elaborated geochemical characteristics of heavy oil in Chagan depression and the main controlling factors of its formation systematically. There are two types of heavy oils:the primary and the secondary. The nonhydrocarbon content of primary heavy oil is higher than the saturated hydrocarbon content. Family component of heavy oils enriched lighter carbon isotope, C29 regular steranes series enriched ααα configuration, low abundance of αββ configuration steranes and no rearranged steranes. It has low tricyclene/pentacyclic terpene value, high gammacerane content, low Pr/Ph value, the oil-forming matrixes were formed under the reducing and high salt water environment, a variety of geochemical parameters indicated that the primary heavy oil derived from the hydrocarbon expulsion of hydrocarbon source rocks at low evolutionary stages. Secondary heavy oil formed after oil and gas migration and accumulation, which has high density, high viscosity and low freezing point due to the change of late preservation condition and secondary reconstruction. The depth of secondary heavy oil was generally less than 1200 meters, most of which were biodegradated oils and some of biodegradated oils experienced multiple period of accumulation. The n-alkanes and isoprenoid of secondary heavy oil suffered from degradation of different level, it indicates that the oil have reached moderate degree of degradation as steranes and terpanes distribute completely. Studies have shown that the thickening of crude oil is the result of a variety of factors worked together, biodegradation is the main formation mechanism of heavy oil in the study area, the later tectonic uplift provide necessary conditions for the crude oil thickened, and active water conditions provide both fine oxidation environment and nutrients for shallow aerobic microbe.
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