巴西被动大陆边缘盆地群大油气田形成条件

基于板块构造演化与岩相古地理特征，确定了巴西东海岸被动大陆边缘盆地群经历了早白垩世巴雷姆期陆内裂谷、阿普特期陆间裂谷、阿尔比期以来的被动大陆边缘3 个原型阶段，分别充填了湖相及河流三角洲、过渡相碳酸盐岩与蒸发岩、海相碎屑岩为主的沉积体系。其中，陆内裂谷阶段湖相烃源岩为大油气田形成奠定了丰富的资源基础；陆间裂谷期碳酸盐岩及被动陆缘阶段海相浊积砂体形成两类优质储集层；陆间裂谷期蒸发岩及被动陆缘阶段海相页岩分别为碳酸盐岩及浊积砂体形成高效区域盖层。裂谷期湖相烃源岩始新世—中新世开始生排烃，油气首先沿裂谷期断层及砂砾岩体进入盐下储集层中，如果不发育盐窗，油气直接被盐岩高效封盖在下伏的以碳酸盐岩为主的地层中，形成盐下碳酸盐岩成藏组合；否则油气则会沿盐运动形成的断层运移至盐上被海相页岩“包裹”的浊积砂体之中富集，形成了“双保险”型大油气田成藏模式。搞清该盆地群大油气田的主控因素与成藏模式，不但深化了被动大陆边缘盆地油气富集规律，而且能为中国石油公司制定南美油气发展战略奠定地质基础。

Build up Conditions of Basin Group Large Oil Gas Field of Passive Continental Margin of Brazil Offshore

Based on the evolution of the tectonic plate and pregeography,the passive continental margin basins on the east coasts of Brazil experienced three prototype phases.Berremian intracontinental rift megasequence in lower cretaceous,comprising lacustrine sediments overlying Neocomian basalts,Aptian intercontinental rift basin,in which the laqoon transitional megasequence deposited,in cluding two sedimentary units:the lower,mostly composed by carbonate and the upper represented by halite,and the drift phase,passive continental margin basin from Albian until the present-day,deposited with the marine megasequence.The Lower Cretaceous lacustrine calcareous black shale is the main source rocks of the giant oil and gas fields.The reservoirs include two sects:lower laqoon carbonatea nd upper,Tertiary and Cretaceous turbidites.The carbonate reservoirs is sealed by halite,while the turbidites are preserved by marine shale.The lower Cretaceous lacustrine source rocks starts to generate the oil and gas from Eocene-Miocene formed"double insurance"type models of giant oil and gas fields.If no salt windows existing,hydrocarbons migrated vertically along faults and are trapped mainly in the pre-salt carbonates.If salt windows exiting,hydrocarbons are accumulated in Upper Cretaceous-Tertiary turbidites which are packaged by marine facies shale.