尼日尔三角洲盆地油气分布特征及控制因素

A study of distribution characteristics of petroleum in Niger delta basin and their controling factors

尼日尔三角洲的形成可分为早、晚两个阶段,早期的白垩纪初期,尼日尔三角洲雏形初具,伴生的火山活动形成的热隆起为第三系有机质转化提供了热源;晚期的古新世—始新世,尼日尔三角洲基本定型,生长断层大量发育,并伴生大量的滚动背斜。滚动背斜基本分为4种:1)简单滚动背斜;2)由两条或多条生长断层与主控断层共同作用下形成的滚动背斜构造;3)由一条或多条反向(北倾)断层与主控断层形成的滚动背斜构造;4)由于页岩向上隆起、造成滚动背斜顶部崩塌而形成的构造。以构造为主的油气藏多与生长断层形成的滚动背斜有关,且发育有非构造圈闭油气藏。继承性发育的巨厚三角洲沉积、良好的生烃条件、稳定发育的储层和盖层及作为主要运移通道的断层等是尼日尔三角洲油气富集的主要控制因素。

Evolution of Niger delta basin can be divided into two stages.During the early stage,i.e.early Creta- ceous,embryonic Niger delta has been formed,and the thermal uplifting associated with volcanic activities has pro- vided heat sources for maturation of Tertiary organic matters.During the late stage,i.e.,Paleocene to Eocene,the framework of Niger delta has been basically finalized,with many growth faults and associated rollover anticlines being developed.The rollover anticlines basically can be divided into 4 types:1) simple rollover anticline;2) rollover an- ticlines that have been formed by the joint action of two or more growth faults and the master fault;3) rollover anti- clines that have been formed by the joint action of one or more antithetic (north-dipping) faults and the master fault; 4) cave-in structures on top of rollover anticlines,due to the uplifting of shale.Most of the reservoirs,mainly of structural type,are related to the rollover anticlines associated with growth faults,and reservoirs of non-structural trap type have also been developed.The major controlling factors of hydrocarbon accumulation in Niger delta include the very thick inherited delta deposits,good hydrocarbon generating conditions,stable and well-developed reservoirs and seals,as well as! faults acting as the major migration pathways.