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首页> 中文期刊> 《地学前缘》 >东非被动大陆边缘盆地演化及大气田形成主控因素:以鲁武马盆地为例

东非被动大陆边缘盆地演化及大气田形成主控因素:以鲁武马盆地为例

         
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东非被动大陆边缘盆地近年来发现了一系列大气田,主要分布于鲁武马盆地,其可采储量达3.8×1012 m3.盆地经历了卡鲁裂谷期、马达加斯加裂谷期和马达加斯加漂移期等3期构造演化.其中,马达加斯加裂谷期形成下侏罗统—中侏罗统湖相-滨浅海相烃源岩,于早白垩世进入生油门限,晚白垩世达到生油高峰,渐新世进入生气窗.受马达加斯加漂移期东非陆上断裂系统活动影响,大量富砂沉积物以块体搬运和深海滑塌方式向深水区堆积,形成了盆地内面积广、厚度大、岩性相对均一且物性良好的超大型深水重力流沉积砂体;漂移期海相泥页岩则为良好的区域性盖层.东非陆上早期隆升和三角洲进积作用使鲁武马盆地形成重力滑动和盐底辟构造,渐新统—上新统内形成东非被动陆缘正断层带(EANFZ)和逆冲断层带(EATFZ),下伏中—下侏罗统烃源岩生成油气沿正断层和深水区逆冲断层向上运移,聚集于构造-岩性-地层、构造圈闭中,形成大气田.%Many giant gas fields,concentrated in the Rovuma Basin of the East Africa passive margin basins,were discovered in recent years with a total recoverable reserves up to 3.8 trillion cubic meters.The Rovuma Basin has gone through three stages of tectonic evolution,i.e.the Karoo rift,Madagascar rift and Madagascar drift.The Lower-Middle Jurassic lacustrine and shallow sea source rocks formed in the Madagascar rift period,and came to the oil window,the peak of oil generation and the gas window,in the Early Cretaceous,the Late Cretaceous and the Oligocene,respectively.Affected by the East Africa onshore faults during the Madagascar drift period,massive sand-rich sediments accumulated towards the deep water region by way of block transport and deep water sliding.It formed a super giant deep-water-gravity-flow sandbody,wide and thick,with relatively uniform lithology and favorable physical property within the basin.The marine mudstone during the Madagascar drift period provided a good regional overlying strata.The early uplift onshore East Africa and delta progradation led to the formation of gravity sliding and salt diapir within the Rovuma Basin,and subsequently the East Africa normal fault zone (EANFZ) and the East Africa thrust fault zone (EATFZ),between the Oligocene and Pliocene.As a result,hydrocarbons from the underlying Lower-Middle Jurassic source rocks migrated upward along the normal and deep water thrust faults,accumulating in the structural-lithological-stratigraphy and structural traps to form the giant gas fields.

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