非洲地区裂谷盆地类型及油气成藏特征

Types and hydrocarbon accumulation characteristics of rift basins in Africa

非洲地区发育多期多类裂谷盆地,油气资源丰富。为指导非洲地区油气勘探与战略选区,对非洲地区裂谷盆地形成期次、类型及重点裂谷盆地的油气成藏特征进行了分析和研究。研究结果表明:①非洲地区主要发育古生代、中生代和新生代3期裂谷盆地,形成卡鲁裂谷系、中西非陆内裂谷系、北非陆缘裂谷系及红海—亚丁湾—东非裂谷系;按原型盆地成因,可划分为与热隆拉张有关的主动裂谷盆地以及与走滑或区域伸展应力场有关的被动裂谷盆地;根据盆地所处构造位置及基底特征,可划分为陆内裂谷盆地、陆间裂谷盆地、拗拉谷裂谷盆地和陆缘裂谷盆地。②因盆地构造演化、沉积充填和结构的不同,导致油气地质特征及油气富集规律存在差异。北非陆缘裂谷盆地发育海相优质烃源岩,以中—新生界含油气系统为主,油气主要富集在差异沉降形成的断垒区;中西非陆内裂谷盆地多期裂谷叠置,主力成藏组合存在较大差异,油气主要分布在古近系、上白垩统、下白垩统不同层系中;东非陆内裂谷盆地形成晚,以新生界含油气系统为主。

There are multi-stage and multi-type rift basins in Africa,with rich oil and gas resources.In order to guide oil and gas exploration and strategic selection of favorable area in Africa,the formation stages and types of rift basins in Africa and the hydrocarbon accumulation characteristics of key rift basins are analyzed and studied.The results show that:(1)there are mainly three stages of rift basins in Africa,namely,Paleozoic,Mesozoic and Cenozoic,forming Karoo rift system,intracontinental rift system in Central and Western Africa,continental margin rift system in North Africa and Red Sea Gulf-Aden-East African rift system.According to the genesis of prototype basins,they can be divided into active rift basins related to thermal-uplift and tension,and passive rift basins related to strike slip or regional extensional stress fi eld.According to the structural position and basement characteristics of the basin,it can be divided into intracontinental rift basin,intercontinental rift basin,aulacogen rift basin and continental margin rift basin.(2)Due to the different tectonic evolution,sedimentary fi lling and structure of the basins,there are differences in petroleum geological characteristics and hydrocarbon enrichment laws.In North Africa,marine high-quality source rocks are developed in continental margin rift basins.The dominant petroleum system is the Mesozoic-Cenozoic system.Oil and gas are mainly accumulated in the faulted horst areas formed by differential subsidence.In the Central and Western Africa,multi-stage superimposed rifts are developed in the intracontinental rift basins with different major source-reservoir-cap assemblages.Oil and gas are mainly distributed in different formations of Paleogene,Upper Cretaceous and Lower Cretaceous.For East African,the formation of intracontinental rift basins were late,which are dominated by Cenozoic petroleum system.