东尼日尔Termit盆地构造演化及古近系油气成藏主控因素

东尼日尔Termit盆地是中西非裂谷系中典型的中-新生代裂谷盆地。盆地主要有早白垩世和古近纪两期断层：前者分布于盆地边界，走向NW-SE;后者在盆地边界和内部均有分布，在边界走向主要与早白垩世断层一致，在内部大多走向NNW-SSE。基于区域构造背景、沉积充填特征及盆地构造特征与前人砂箱模拟实验结果的对比研究认为，盆地经历了早白垩世正向引张作用和古近纪斜向引张作用，且正向-斜向引张作用对盆地构造特征和演化有重要控制作用。早期正向引张作用形成与基底前泛非期变质带近平行的早期断层，晚期斜向引张作用使后期断层特征主要受先存构造和伸展方向的控制，表现为：在盆地边界，后期断层受早白垩世断层影响较大，走向与先存构造近平行；在盆地内部和早期断层不发育的构造区域，后期断层主要受伸展方向控制，走向与其近垂直。通过对古近系油气分布特征和断层活动性研究，分析了该区油气成藏主控因素：Sokor2组区域性盖层控制油气垂向分布，断块圈闭的岩性侧向封堵条件控制圈闭有效性，古近纪裂陷期的断裂活动控制油气平面和含油气层系分布。在明确成藏主控因素基础上，建立了古近系油气跨世代聚集模式。

Structural evolution and main controlling factors of the Paleogene hydrocarbon accumulation in Termit Basin, eastern Niger

The Termit Basin is a typical Mesozoic-Cenozoic continental rift basin in the central and western African rift system.The basin is characterized by two distinct systems of normal faults in terms of activity timing,and these systems were formed in Early Cretaceous and Paleogene,respectively.The former is mainly composed of rift-border faults trending NW-SE;whereas the latter develops both in the basin margin and the interior,striking parallel to the Early Cretaceous faults on the basin margin and NNW-SSE within the interior of the basin.An integrated study on regional structural backgrounds,depositional filling and a comparison between fault architectures of the basin and analogue models of laboratory experiments reveals that the basin experienced an orthogonal extension in Early Cretaceous and an oblique extension in Paleogene,which significantly affects the structural features and evolution of the basin.During the first extension period,NW-SE trending faults sub-parallel to the pre-Pan-African metamorphic belts were formed due to the orthogonal extension.In the second extension period,late faults were mainly controlled by the pre-existing structure and extension direction.On both margins of the basin,strikes of the late faults greatly influenced by Early Cretaceous faults are sub-parallel to the pre-existing faults.However,within the basin and in the domains where Early Cretaceous faults are not well developed,the extension direction used to play a major role in the development of late faults,with their strikes sub-perpendicular to the extension direction.Based on the knowledge of hydrocarbon distribution characteristics and fault activities,we illustrated main controlling factors for the Paleogene hydrocarbon accumulation,which include: the vertical distribution of oil and gas is controlled by regional cap rocks of the Sokor 2 Formation;the efficiency of faulted blocks is determined by lateral lithologic sealing of traps;the spatial distribution of hydrocarbons and oil-bearing strata is determined by fault activities of the Paleogene extension.The Paleogene hydrocarbon accumulation model was then proposed on the basis of having understood these main controlling factors.