尼日尔三角洲盆地海陆过渡区油气成藏规律

从区域地质着手,通过对比分析,总结了尼日尔三角洲盆地海陆过渡区石油地质特征及其油气成藏规律与成藏主控因素,认为:尼日尔三角洲盆地是伴随冈瓦那古大陆解体与大西洋扩张发育形成的典型被动大陆边缘型盆地,主要经历了早白垩世晚期-晚白垩世桑托期的裂谷阶段以及晚白垩世坎佩尼期以来的漂移期2个主要演化阶段.盆地主体是新生代三角洲,沉积厚度达到12 km以上,包括Akata组、Agbada组和Benin组3个穿时的岩性地层单元.其中最下部的Akata组为大陆架-大陆坡的前三角洲、浅海-深海相厚层泥页岩,亦是研究区主要烃源岩;中部Agbada组主要是三角洲前缘砂体、海底扇砂体等,是区域油气藏储集层发育层段;上部Benin组则主要是陆相河流及岸后沼泽沉积,多发育互层泥岩,构成区域的主要油气藏盖层.由于Akata组塑性泥岩段主要以流动构造为特点,引起上覆地层发育重力构造,构造样式在平面上具有明显的分带性,陆地和陆架浅海区发育大型伸展构造.研究区发育区域性生长断裂,其控制的构造格局与圈闭样式是油气聚集与成藏的主控因素.

Study on hydrocarbon accumulation of the sea-onshore transitional zone in Niger Delta Basin

According to the comprehensive analysis of regional hydrocarbon geological features,hydrocarbon accumulation law and main control factors of hydrocarbon accumulation in the sea-onshore transitional zone,it is held that Niger Delta Basin is a typical passive continental margin basin,which was developing with the disintegration of the ancient Gondwana continent and the expansion of the Atlantic.Its development includes two main evolution periods,the rifting period from the late stage of early Cretaceous to Santo stage of late Cretaceous and the following drifting period since Campanian of late Cretaceous.Cenozoic delta is the main part of the basin,and its biggest depositional thickness is about 12 km.The deposit includes three diachronic lithostratigraphic units of Akata Formation,Agbada Formation and Benin Formation.Akata Formation in the lower is mainly the prodelta of continental shelf and continental slope and the thick shallow——deep marine mud shale,which is the main hydrocarbon source rock in the studied area.Agbada Formation in the middle mainly includes the delta front sand and submarine fan sandbodies,which is the regional reservoir.Benin Formation on the top is the continental fluvial deposit and swamp deposit,which is the main regional cap rock.The plastic mudstone layer in Akata Formation is characterized flow structure,which will cause that overlying strata,such as Agbada Formation,developed gravity structures.And the structural style presents obvious zonality,and large extensional tectonics developed in land and shallow sea zone.Regional growth faults developed in the studied area,by which the tectonic framework and the trap style controlled are main control factors of the hydrocarbon accumulation.