东非鲁伍马盆地深水沉积体系及油气勘探意义

Deep water depositional system in Rovuma Basin, East Africa and its bearing on hydrocarbon exploration

  • 摘要: 利用高分辨率三维地震资料、测井和钻井数据,对东非鲁伍马盆地深水沉积特征进行了系统刻画。根据深水沉积体的地震相特征,识别出峡谷、水道、漫溢沉积、朵体、块体搬运沉积(MTDs)和凝缩段等深水沉积单元,建立了地震识别图版。分析总结了水道和朵体的岩性特征、电性特征和储层物性特征,砂岩具有低伽马(GR)和高电阻(RT)特征,厚层砂岩GR曲线呈“箱型”,有泥岩夹层的砂岩段呈叠加的“钟型”特点;储层压实程度弱,发育原生粒间孔隙,具有中—高孔、中—高渗的特征。结合成藏条件研究,认为由水道和朵体浊积砂岩储层、凝缩段和漫溢沉积泥岩盖层、天然堤和MTDs为侧向遮挡等要素构成的油气储、盖配置关系,是研究区油气成藏的一个关键因素,对深水油气勘探具有一定的指导意义。

     

    Abstract: Based on the high-resolution 3D seismic data, in addition to well logging data and drilling data, the deep-water deposits in the Rovuma Basin of East Africa are systematically studied in this paper. According to the seismic facies of the deep-water depositional bodies, the architectural elements of the system, such as the canyon, channel, overbank, lobe, mass-transport deposits (MTDs) and condensed layers are recognized, and the seismic identification criteria established, while the lithologic, electrical and reservoir-physical characteristics are analyzed and summarized. Sandstones are usually low in gamma ray (GR) and high in electrical resistance (RT). The GR curve of thick sandstone is “boxlike” and the sandstone sequence intercalating mudstone layers in superimposed “bell-shape”. The compaction of reservoirs is rather weak and the primary intergranular pores are relatively developed, and, therefore, medium to high porosity and permeability are widely developed. The overall study of reservoir forming conditions suggest that there occur a good hydrocarbon forming system with channel and lobe turbidite sandstone as reservoirs, condensed section and overbank mudstone as caprocks, and levee and MTDs for lateral plugging. The model has significant implications for deep-water oil and gas exploration.

     

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