尼日尔三角洲盆地深水沉积体系特征

Depositional Characteristics of Deepwater Systems in the Niger Delta Basin

尼日尔三角洲盆地深水沉积研究是目前世界油气勘探的热点问题之一.通过对三维地震资料、岩心及测井曲线分析,揭示了尼日尔三角洲盆地南部地区新近系深水沉积体系特征.基于不同属性的层序界面识别,研究区划分出SQ1-SQ6共6个三级层序,并建立层序地层格架,进而总结出研究区深水沉积模式.研究区除堆积正常半深海-深海泥岩外,还广泛发育海底扇沉积,海底扇由浊积水道和海底扇朵体组成,其中水道分支少、弯度大,外部形态类似曲流河;朵体平面上成朵叶状分布,可以划分为末端朵体和决口扇朵体.研究区新近系地层自下向上由老到新,相对海平面先下降再上升,SQ1-SQ4层序以海底扇朵体沉积为主,SQ5-SQ6层序以浊积水道沉积为主.

The research of deepwater sedimentary systems in the Niger Delta basin is one of the key issues in hydrocarbon exploration in the world. According to the analysis of 3D seismic data, well, core, sedimentary structure and logs characters, depo sitional characteristics of deepwater systems are discussed on Neocene in the south of Niger Delta basin. Sequence stratigraphic framework is established based on identification of sequence boundary and 6 third-order sequences are divided and named as SQ1-SQ6. The depositional models of deepwater sedimentary systems are established. Three kinds of depositional facies are identified in the deepwater sedimentary systems, namely, turbidite channel, submarine lobe and hemipelagic mudstones. Channel only has few branches that are highly sinuous, with morphology similar to that of meandering river; submarine lobes can be divided into terminal lobe and crevasse splay lobe. During the Neocene deposition from the SQ1 to the SQ6, relative sea level firstly fell and then rose, submarine lobe facies developed in the SQ1 SQ4 and turbidite channel facies developed in the SQ5-SQ6.