Oil & Gas Geology ›› 2011, Vol. 32 ›› Issue (5): 733-742.doi: 10.11743/ogg20110512

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Identification of the shelf margin delta in sequence stratigraphic frameworks and its significance: a case study of the Baiyun Sag,South China Sea

Xu Qiang1, Wang Yingmin2, Lü Ming1, Wang Dan1, Li Dong2, Wang Yongfeng2   

  1. 1. Research Center of CNOOC,Beijing 100027,China;
    2. China University of Petroleum,Beijing 102249,China
  • Received:2011-03-20 Revised:2011-09-06 Online:2011-10-28 Published:2011-12-16

Abstract:

Shelf margin delta is characterized by high-quality combination of source rocks,reservoirs and caps,and multiple trap types.Based on genetic styles,it can be classified into three types:provenance-dominated type,sea level-dominated type and hybrid type.During the relative quiescence period of sea-level,large amount of sediments are transported to the continental slope by rivers,making the shelf break gradually move seaward.Then shelf margin delta deposits could be formed at the shelf break and continental slope.Moreover,during period with relative stable sediment supply,the lowering of sea level to the shelf break also can transport large amount of sediments crossing broad continental shelf to shelf break,forming shelf margin delta deposits.These characteristics make shelf margin delta system identifiable in sequence stratigraphic framework.For example,shelf margin delta often shows large 'S' progradational reflection structure on seismic profiles,and the thickness between top surface and bottom surface can reaches up to hundreds of meters,much thicker than that within continental shelf.Moreover,the shelf margin delta usually occurs in lowstand system tract and is characterized by landward and seaward slope wedges.Based on integrated analysis of recent well logs and high-resolution 3D seismic data from Baiyun sag,a series of Oligocene-Miocene shelf margin deltas were identified in the Zhuhai Formation and Zhujiang Formation,and some unique deep-water reservoir systems were also recognized in the shelf break.These understandings will be helpful to future deep-water exploration.

Key words: deep-water area, shelf margin delta, sequence stratigraphy, Baiyun Sag, South China Sea

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