准噶尔盆地车排子地区稠油成因及成藏过程

摘要

Heavy oils are discovered in Jurassic,Cretaceous and Neogene reservoirs of Chepaizi uplift in the western margin of Junggar Basin.Based on the detailed analysis of geochemical characteristics of heavy oil,according to the characteristics of n-alkanes,isoprenoids,steroids and triterpenes biomarkers and stable carbon isotope compositions, the sources,origin and biodegradation of heavy oil in Chepaizi area were discussed by the means of reservoir geochemistry and molecular geochemistry;according to the fluid inclusions combined with geological structure and source rocks,the accumulation period and migration of heavy oils were analyzed,and the hydrocarbon accumulation process was established.The results show that the heavy oils in Chepaizi area of Junggar Basin are subjected to different degrees of biodegradation,mainly derived from Permian source rocks of Changji sag,and some of them mix with crude oil from Jurassic source rock;heavy oil reservoirs are secondary by later reformation,and there are two major stages of hydrocarbon accumulation;the first period is from Cretaceous to Paleogene,the accumulation mainly happens in Jurassic and Cretaceous reservoirs,and the second period is after Neogene,the accumulation mainly happens in Neogene Shawan Formation reservoirs;heavy oils mainly migrate through Hongche fault belt and unconformity surface,and are subjected to a slight degradation during accumulation or migration and to a more severe degradation after accumulation.%准噶尔盆地西缘车排子凸起侏罗系、白垩系和第三系均发现了稠油。运用油藏地球化学及分子地球化学方法，在对稠油地球化学特征精细剖析的基础上，根据原油的正构烷烃、类异戊间二烯烷烃、甾萜烷烃类生物标志物特征和稳定碳同位素组成特征，讨论车排子地区稠油的成因及生物降解程度，分析稠油的油源；根据流体包裹体资料并结合区域构造和烃源岩资料，分析研究区稠油的成藏期次和运移途径，建立稠油油藏的成藏模式。结果表明：准噶尔盆地车排子地区稠油主要来源于昌吉凹陷二叠系烃源岩，部分有侏罗系烃源岩生成原油的混源，均受到不同程度的生物降解；稠油油藏为后期调整形成的次生油藏，存在两期成藏过程，第1期为白垩纪到古近纪，主要存在于侏罗系和白垩系储层中，第2期为新近纪以来，主要存在于新近系沙湾组储层中；稠油主要通过红车断裂带和不整合面运移，而且运移时伴随着生物降解，在聚集成藏前或运移前已经遭受了轻微生物降解作用，聚集成藏后又遭受了较为严重的生物降解作用。