北部湾盆地涠西南凹陷稠油特征及成因机制

Characteristics and Genetic Mechanisms of Heavy Oil in Weixi'nan Sag,Beibuwan Basin

涠西南凹陷位于北部湾盆地北部坳陷带,稠油主要分布在新近系角尾组、下洋组,原油表现为高密度、高黏度、高胶质沥青质和低含硫量的特征。根据原油物性分布、地球化学指标、油源对比,结合区域地质条件,探讨了本区稠油油藏的基本特征和成因模式。该区稠油属于次生成因,纵向分布正好处于微生物发育的强烈降解带,受生物降解作用影响明显,而地下水流动过程中发生的水洗作用,进一步加剧了本区原油的稠化。

In Weixi'nan sag,northern depression of Beibuwan Basin,heavy oil is mostly distributed in the Neogene Jiaowei and Xiayang formations,and often indicates some features of high density,viscosity,and colloid asphaltene,and low sulfur content.For heavy-oil reservoirs in this study area,the basic characteristics and genetic mode were analyzed according to crude physical properties and geochemical indices,oil source correlation,and regionally geological conditions.Results show that in this area,heavy oil is of secondary genesis;it is just distributed longitudinally at a strong biodegradation belt with well developed microorganisms;and affected obviously by bio-degradation,water washing in the process of underground-wa-ter flowing may intensify crude-oil thickening.