东非被动大陆边缘盆地构造—沉积特征及其对大气田富集的控制作用

摘要/Abstract

摘要： 东非海域近5年来发现了一系列大气田，主要分布于鲁武马盆地和坦桑尼亚盆地，可采储量达3.8×10¹² m³。通过区域构造演化、盆地构造—沉积特征研究，认为该区主要经历了3期构造—沉积演化阶段：①晚石炭世—早侏罗世卡鲁裂谷期，以河流相、湖相和三角洲相沉积为主；②中侏罗世—早白垩世马达加斯加裂谷期，以陆相和浅海相沉积为主，发育主力烃源岩；③晚白垩世—第四纪马达加斯加漂移期，以被动大陆边缘沉积为主，海底扇、斜坡扇和重力流水道等浊积砂岩构成主力储层，泥岩构成良好的区域性盖层。大气田主力成藏组合包括鲁武马盆地渐新统—上新统、古新统—始新统砂岩及坦桑尼亚盆地渐新统、上白垩统砂岩。鲁武马盆地大气田主要分布于深水区逆冲断层带及其前缘，重力滑塌和侏罗系盐底辟构造使鲁武马三角洲前缘广泛发育逆冲断层带，逆冲断层成为良好的油气运移通道，油气自深部烃源岩向上运移、聚集于逆冲断层带砂岩储层中；坦桑尼亚盆地大气田主要分布于斜坡重力流水道砂岩中，南北向正断层控制油气富集。

关键词: 被动大陆边缘, 深水逆冲断层带, 盐底辟, 海底扇, 重力流水道, 鲁武马盆地, 坦桑尼亚盆地

Abstract: In the past five years, a number of giant gas fields have been discovered in offshore East Africa. They are mainly located in Ruvuma and Tanzania Basins, with total recoverable reserves of 3.8?0¹² m³. It is indicated by regional tectonic evolution study and basin structure-sedimentation characteristics analysis that the basins in East Africa mainly experienced three phases of structural-sedimentary evolution, including: (1) Karoo rift period of Late Carboniferous to Early Jurassic, with dominant sedimentary facies of fluvial, lacustrine and delta; (2) Madagascar rift period of Middle Jurassic to Early Cretaceous, with dominantly continental and shallow marine facies, the principal source rocks developed; and (3) Madagascar drift period of Late Cretaceous to Quaternary, with dominantly passive continental margin sedimentation, with turbidite sandstones of abyssal fan, slope fan and gravity flow channel as major reservoirs and the shales as regional cap rocks. Major plays of the giant gas fields are Oligocene-Pliocene, Paleocene-Eocene sandstones in the Ruvuma Basin, and Oligocene and Upper Cretaceous sandstones in the Tanzania Basin. In Ruvuma Basin, the giant gas fields are mainly located at deep-water thrust belts and their fronts. Thrust belts are widely developed at Ruvuma front due to gravity collapse and Jurassic salt diaper, and they act as good migration pathways for oil and gas. Oil and gas migrates upwards from the deep source rocks and accumulates in sandstone reservoirs of thrust belts. In Tanzania Basin, giant gas fields are mainly located at the gravity flow channel sandstones of slopes, and oil and gas accumulation is controlled by the S-N normal faults.

Key words: passive continental margin, deep-water thrust belt, salt diapir, abyssal fan, gravity flow channel, Ruvuma Basin, Tanzania Basin

张光亚　刘小兵　温志新　王兆明　宋成鹏. 东非被动大陆边缘盆地构造—沉积特征及其对大气田富集的控制作用[J]. 中国石油勘探, 2015, 20(4): 71-80.

Zhang Guangya, Liu Xiaobing, Wen Zhixin, Wang Zhaoming, Song Chengpeng. Structural and Sedimentary Characteristics of Passive Continental Margin Basins in East Africa and Their Effect on the Formation of Giant Gas Fields[J]. China Petroleum Exploration, 2015, 20(4): 71-80.

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