北部湾盆地断裂构造特征及其对油气的控制作用

Characteristics of fault structure and its control on hydrocarbons in the Beibuwan Basin

北部湾盆地主要发育早期伸展断裂、中期走滑伸展断裂、晚期伸展断裂和长期活动断裂等4种断裂类型。盆地演化总体经历了古近系裂陷期和新近系坳陷期两大演化阶段。盆地伸展裂陷期主要有3期断裂活动,在古新世—始新世形成NE向、NEE向伸展断裂;渐新世在走滑伸展作用下形成了NEE向走滑伸展断层和近EW向次级断层。断裂的形成和演化控制了生烃洼陷的分布和促进了烃源岩的热演化,形成多种类型圈闭,为油气垂向运移提供了主要的运移通道。与生油洼陷相邻且长期继承性活动的断裂带和凹陷中央的隆起带是油气聚集的最有利区域。

The present paper studied characteristics of the fault development and activities in the Beibuwan Basin and discussed control factors of the fault formation and evolution on hydrocarbon reservoirs.The study showed that four types of faults developed in the Beibuwan Basin,including the early rift fault,middle strike-slip extension fault,late extension fault and long-term active fault.In Cenozoic,the Beibuwan Basin experienced both evolutionary stages,i.e.the rifting stage in Paleogene and the subsidence stage in Neogene.There were three major periods of fault activities in the extensional rifting stage.There formed NE-and NEE-direction extension faults during Paleocene and Eocene.In Oligocene,NEE-direction strike-slip extension faults and approximately EW-direction sub-faults were formed under the influence of strike-slip extension.The formation and evolution of faults controlled the distribution of hydrocarbon generative depressions,accelerated the thermal evolution of source rocks to generate various traps of hydrocarbons and provided major pathways for hydrocarbon migration.Zones with long-term active faults adjacent to hydrocarbon generative depressions and central uplift zones in depressions are the most favorable area for hydrocarbon migration and accumulation.