尼日尔三角洲高分辨率层序地层及沉积相研究——以尼日利亚M区块为例

High-resolution sequence stratigraphy and sedimentary facies:A case study of the block M in the Niger delta,Nigeria

本文采用高分辨率层序地层学理论,研究尼日尔三角洲中尼日利亚M区块的层序及沉积特征。选择基准井对全井段的岩屑资料进行细致的观察描述,确定自然伽马、声波等曲线对岩性的响应特征;解释主要钻井的岩性剖面;根据岩性剖面,参照地震剖面中揭示的钻井相对于沉积倾向剖面中所在的位置,选择相应的模型划分不同级别的基准面旋回;通过对钻井基准面旋回的形态、厚度、出现频率等属性特征的分析,进行基准面旋回对比,建立等时的层序格架。研究总结了不同级次旋回界面和旋回类型的识别特征,将研究层段分为9个长期旋回。基于对该区构造、沉积背景、物源供应状况及演化特征,分析了该区三角洲的基本类型、随层序及体系域的时空演化等要素。总结了分流河道、水下分流河道、砂坝等若干骨架沉积微相的旋回组合特征、叠加样式等,为储、盖组合及勘探目标评价提供了的依据。

The sequence stratigraphy and sedimentary characteristics are dealt with for the block M in the Niger delta,Nigeria on the basis of high-resolution sequence stratigraphic theory,including the description of lithoclastics data from the whole wells,determination of responses of GR and AC to lithology,interpretation of lithologic sections of major wells,division and correlation of base-level cycles of varying orders,and construction of isochronous sequence stratigraphic framework.Nine long-term cycles are discriminated on the basis of cycle boundary and types.The types and spatio-temporal evolution of deltas in response to the sequences and systems tracts are discussed in the light of regional tectonics,sedimentary background and sediment supply.Finally the present paper gives a summary of cycle associations and stacking patterns of the sedimentary microfacies such as distributary channels,subaqueous distributary channels and sandbars aiming at providing the evidences in favour of the assessment of reservoir-seal associations and exploration targets.