准噶尔盆地西北缘车排子凸起上、下层系原油的地球化学特征差异及其意义

Differences in Geochemical Characteristics of Oils Trapped in the Upper and the Lower Series of Strata of Chepaizi Uplift Along Northwest Margin of Junggar Basin and Their Significances

根据原油物性、化学组成、生物标志化合物以及稳定碳同位素等特征,将准噶尔盆地车排子地区各层系的原油划分为2组:一组是储集在侏罗系及以下层系的原油(下层系原油),另一组是储集在白垩系及以上层系的原油(上层系原油)。同一组原油的物理和化学特征相似,而不同组的原油则相差较大。下层系原油为同一来源,来自二叠系烃源岩;上层系原油亦为同一来源,主要来自侏罗系。利用含氮化合物分布特征对该区进行油源划分和对比的结果与用密度、粘度、原油族组成和生物标志化合物等参数所得到的结果完全吻合,可见含氮化合物也可以用于原油类型划分和油源对比方面的研究。最后建立了车排子凸起的油气成藏模式:车排子凸起紧邻凹陷,油源条件充足;构造位置有利,是油气运移的优势指向区;该区发育的众多断层和不整合面,为油气的运移提供了良好的通道。油气沿断裂垂向运移时遇到不整合面则发生侧向运移,从而在空间上构成'Z'字形或呈阶梯状的运移路线,最终形成油藏类型多、含油层系多的成藏面貌。

Oils from intervals in the Chepaizi areas of Junggar basin are divided into two groups based on physical properties,chemical components,biomarkers and stable carbon isotope composition of the oils.One group includes the oils trapped in the reservoir beds of Jurassic and the beds below Jurassic（named as the lower series of strata oils）,and another one includes those in reservoir beds of Cretaceous and the beds above Cretaceous（named as the upper series of strata oils）.The oils in same group have similar physical and chemical characteristics,while those in different group are of differences in these characteristics.The lower series of strata oils have the same source and come from the Permian source rock,and the upper series of strata oils have the same source as well and are from mainly the Jurassic rock.Results of oil-sources division and correlation for these oils by making use of nitrogen compounds distributions are completely identical with those by density,viscosity,group composition and other biomarker parameters just mentioned above,indicating that nitrogen compounds could be used in oil-sources division and correlation.Finally,oil-pool forming model is established for the Chepaizi uplift.it is just next to sag areas with favorable structural location,and has abundant oil-gas resources.The uplift is the dominant destination for hydrocarbon migration.Multiple faults and uncomformable surfaces of this area form excellent migration pathways.Lateral migration happened when oil and gas migrating vertically along faults encountered uncomformable surfaces.Thus in the space Z-chart or a ladder migration routes form and finally multiple oil pool types and hydrocarbon-bearing layers are formed.