西非被动大陆边缘盆地群大油气田形成条件与成藏模式

Major Oil and Gas Fields Formation Conditions and Accumulation Models of West African Passive Continental Margin Basins

以板块学说为理论基础,利用IHS能源信息库及新项目评价资料,从西非被动大陆边缘盆地群原型盆地入手,系统剖析了该区大油气田的形成条件与主控因素,建立了大油气田3类成藏模式。研究认为,西非经历了早白垩世贝利亚斯期至巴雷姆期陆内裂谷、阿普特期陆间裂谷、阿尔必期以来的被动大陆边缘3个原型阶段,分别充填了陆相、过渡期泻湖相及漂移期海相沉积体系。陆内裂谷湖相及漂移海相沉积形成了"下湖上海"两套优质烃源岩;过渡早期海侵砂砾岩,漂移期碳酸盐岩、三角洲、深水浊积砂体形成了多套优质储集层;过渡晚期盐岩及漂移期海相页岩分别为盐上及盐下大油气田形成了高效区域封堵。以此为依据,分别建立了南段"盐岩不发育裂谷型"、中段"盐岩发育双层型"及北段"高建设性三角洲型"3类大油气田成藏模式。该研究不但深化了被动大陆边缘盆地油气富集规律,而且能为我国石油公司在该类盆地新项目评价中提供充分的地质依据。

Based on plate tectonics, using IHS Energy Information Database and evaluation data of new pro- jects, starting from the prototype basin research of West African passive continental margin basins, the condi- tions and main controlling factors of the formation of major oil and gas fields in this area, are systematically ana- lyzed. Three kinds of oil and gas accumulation models of major oil and gas fields are established. West African experienced three prototype stages： Early Cretaceous Neocomian to Barremian intracontinental rift stage, Aptian intercontinental rift stage and passive continental margin stage since Albian, respectively filled by continental fa- cies, transitional lagoonal facies and drift stage marine facies. Intracontinental rift lacustrine facies and drift stage marine facies formed two sets of premium source rocks. Transgressive glutenite facies developed in the early transitional period and carbonatite, delta facies and deep water turbidite sandstone facies developed in drift stage, are high quality reservoirs. Salt rocks developed in late transitional period and marine shale developed during drift stage act as high efficiency regional seals respectively for oil and gas fields beneath and over the salt rocks. Ac- cordingly, we established three kinds of oil and gas accumulation models, which are rift type with little salt rocks in the southern region, double layer type with abundant salt rocks in the middle region and high constructive delta type in the northern region. This research not only deepens the understanding of hydrocarbon enrichment rules in West African passive continental margin basins, but also can help to evaluate new projects in this area.