涠西南凹陷南部斜坡带油气运移地球化学与成藏特征

Geochemical effects of hydrocarbon migration and characteristics of accumulation in the south slope of the Weixinan depression

涠西南凹陷南部斜坡带是重要的油气聚集区,在角尾组、涠洲组、流沙港组和石炭系地层中均发现了油气显示。通过原油地球化学特征分析,本区原油主要为凹陷中央流沙港组二段下部烃源岩生成的成熟原油,原油以轻质油为主,为咸水湖相环境形成原油。油源精细对比揭示,涠西南凹陷流沙港组二段、三段、角尾组和石炭系地层均属于同一类原油,通过全烃谱图中正构烷烃分布特征建立适合本区的运移分馏指数FI=(nC8~nC12)/(nC25~nC32),并结合饱和烃、芳烃比值和油气运移分馏指数关系分析,WB到WC流沙港组二段和流沙港组三段原油样品均呈现出运移分馏指数增加,饱芳比增加的趋势,指示WB构造流沙港组二段和流沙港组三段原油为侧向运移至WC构造。同时通过WA构造含氮化合物含量与深度关系分析,揭示浅部含氮化合物屏蔽型异构体相对富集,暴露型异构体相对减少,指示垂向上具有明显的沿断裂带从深部向浅部运移的特征。综合考虑本地区输导体系的空间叠置关系,认为南部斜坡带是洼陷中央烃源生成油气经由断层、砂体等输导体系运聚到浅部和斜坡带成藏,此次研究对本区带下步油气勘探具有重要意义。

Weixinan depression is a rich hydrocarbon generation sub-sag;oil and gas reservoirs have be found in the Jiaowei Formation,Weizhou Formation,Liushagang Formation,and Carboniferous strata.The relationship between the oil and the geochemical characteristics of crude oil is identified by comparing them.Based on similar maturity of crude oil in this region,adopt the migration fractionation effect means for oil and gas migration direction specified Through the alkanes distribution of whole hydrocarbon chromatogram to establish a suitable migration fractionation index,to use the characteristics of DST test oil physical property and composition to analysis of the migration path.By alkyl benzothiophene and nitrogen compounds migration differentiation phenomenon in the migration process to prove oil and gas lateral migration and vertical migration.Considering spatial superimposed relationship of transportation systems in this region,analysis of the characteristics of crude oil transported accumulation pattern in this area.Studies have shown that oil and gas generated from the central hydrocarbon source through faults unconformity surface transportation systems shipped to shallow and high formation reservoirs in the south slope belt.