东营凹陷含烃流体驱动过程中的地球化学效应

油藏中烃类的地球化学特征具有明显的非均一性,油气运移和成藏过程对其有重要的影响。以东营凹陷为例,在不同流体压力系统成藏条件研究、烃源岩与储层的烃类地球化学差异对比的基础上,综合分析了烃类的驱动机制。在以古近系为烃源岩的陆相断陷盆地(凹陷)中,垂向运移的影响大于横向运移,总体表现为饱和烃的轻/重比(nC21+nC22)/(nC28+nC29)随运移变低,表征原油成熟度的甾烷异构化参数C29ββ/(αα+ββ)也随运移方向变小,成藏过程中动力和阻力相互作用导致的运移和保存之间存在一定的平衡关系,同时影响了油气组分的变化,反之则相反。在研究东营凹陷烃类驱动过程中地球化学分异机制的基础上,明确了不同流体单元的差异性及其对烃类地球化学特征的影响,深入分析了不同区带的油气运移及成藏方式。

GEOCHEMICAL EFFECTS OF THE MOVEMENT OF HYDROCARBON BEARING FLUID: A CASE STUDY IN DONGYING SAG

In the Dongying Sag, reservoirs were formed in different pressure systems.The geochemical heterogeneity of hydrocarbons in the reservoir could be affected by hydrocarbon migration and accumulation.In this paper, we investigated the geochemical differences of hydrocarbon between source rocks and reservoir fluids for further understanding of the driving mechanism of hydrocarbons.Our results suggest that in a continental fault basin (or sag) like the Dongyiing Sag, source rocks occur in the Paleogene, the geochemical effects caused by vertical migration are greater than those by lateral migration.The light/heavy saturated hydrocarbons ratios (nC21+nC22)/(nC28+nC29) and the petroleum maturity indicator sterane ratios C29ββ/(αα+ββ) decrease with the migration distance.The balance between migration and preservation resulted from the interaction of dynamics and resistance affects the composition of hydrocarbon, and vice versa.The study of differentiation mechanisms during hydrocarbon migration in the Dongying Sag reveals that the discrepancies in different fluid units and its effects on hydrocarbon geochemical characteristics were recognizable, that is helpful for further study of migration and reservoir-forming modes in different zones.