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西非被动大陆边缘盆地群是近年来全球油气资源的快速增长区。为揭示加蓬海岸盆地的油气富集规律,对盆地的构造特征、盐层序、成藏组合和油气成藏模式进行了研究,结果表明:裂谷期、过渡期和漂移期3个演化阶段中发育的2组近于垂直的NW—SE向和NE—SW向断裂体系形成了东西分带、南北分块的盆地构造格局。盐层序是该盆地油气富集的关键因素,其流动变形形成的盐构造圈闭有利盐上油气聚集成藏;由于不发育盐滑成因的盐窗,盐层序依然保持着连片性,给盐下油气提供了良好的封盖条件。不同时期盐构造演化差异明显,康尼亚克期—始新世早期是盐构造发育的主要时期,对应于第Ⅲ枢纽带活跃期,形成了大量伸展成因的盐构造,盐底辟速率约等于沉积速率,控制了沉积相分布并形成了大量构造或构造—地层圈闭;始新世晚期—渐新世早期,构造反转使局部地区发育挤压成因的无根盐株;后渐新世,盐底辟速率小,对沉积作用影响微弱,有利圈闭发育有限。综合分析表明,盐下有利成藏组合主要发育在第I枢纽带断陷周围的断块和断背斜等圈闭中,盐上有利成藏组合主要分布于第Ⅲ枢纽带西侧浊积扇相区与盐构造圈闭的叠加区。
The passive continental margin basin in West Africa is a rapidly growing area of global oil and gas resources in recent years. In order to reveal the laws of hydrocarbon enrichment in the coastal basin of Gabon, the tectonic characteristics, salt sequence, reservoir-forming assemblages and hydrocarbon accumulation patterns in the basin have been studied. The results show that in the three evolution stages of rifting, transition and drift There are two sets of NW-SE and NE-SW fault systems developed in the eastern and western parts of the basin and the north-south block basin. Salt sequence is the key factor of oil and gas accumulation in this basin. The hydrocarbon formed by the flow deformation and salt accumulation in the favorable salt pool accumulates and accumulates. Because of the salt window without salt slip formation, the salt sequence still remains contiguous, Provides good capping conditions for hydrocarbons under salt. The evolution of salt structure evidently from different periods. The Connellian-Early Eocene was the main period of salt tectonic development. Corresponding to the active period of the third hinge belt, a large amount of salt structure was formed, and the salt dipping rate was about equal to Sedimentation rate, controlling the distribution of sedimentary facies and forming a large number of structures or formations - stratigraphic traps. From the Late Eocene to early Oligoceses, the rootless salt strata that reverse the tectonic inversion resulted in the development of extrusion in some areas. After Oligocene , The rate of salt diapirism is small, the impact on sedimentation is weak, and the favorable trapping development is limited. The comprehensive analysis shows that favorable sub-salt assemblages are mainly developed in fault blocks and faulted anticline traps such as faults around the I-hinge belt. The favorable salt accumulation assemblages are mainly distributed in the turbidite fan facies on the west side of the third pivot belt Area and salt structure traps superimposed area.