Neogene Shallow Water Deltaic System and Large Hydrocarbon Accumulations in Bohai Bay, China
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摘要: 新近纪渤海具有构造稳定、沉降缓慢、湖泊水域范围大、内部无分割、地形平缓、坡度小等特点,广泛发育浅水三角洲,从而形成渤海海域新近系良好的储盖组合和优越的油气成藏条件。浅水三角洲砂岩储层由于受河流作用的控制,砂体具有明显的方向性,存在明显的分叉现象,与曲流河相比,砂体连通性较好,砂体等厚图呈典型的朵叶状。湖相厚层泥岩普遍发育,与浅水三角洲砂体组成多套垂向优质储盖组合。浅水三角洲发育于渤海新近纪至今处于生烃的峰期主力富烃凹陷的有利区带,新构造运动造成新近纪以来凹陷主力源岩生烃峰期与新构造运动的同步耦合,为渤海大型浅水三角洲成因的优质储层油气成藏创造了优越条件,可以形成大型油气田。因此,重视并充分挖掘渤海浅水三角洲储层类型油气藏的勘探潜力将是追求浅层优质油藏、进一步增储上产的方向所在。Abstract: Bohai basin is characterized by tectonicallyuniform block with steady and slow subsidence, which resulted in lowrelief, low gradient, and highstand lakelevel depositional settings during the Neogene. Excellent reservoirseal combinations and superb conditions for the formation of hydrocarbon traps in the region. Cyclic depositions of shallow water deltaic system which were dominated by fluvial systems showed obvious lobe shape on contour maps and very good lateral connectivity between lobes. Broadly developed, vertically stacked cyclic thick shale layers resulted in multiple sets of reservoirseal combinations. Shallow water deltaic facies are positioned near the prolific hydrocarbonenriched depressions which have been in the peak hydrocarbon generation since Neogene. And the coincidence of neotectonism since Neogene and the peak hydrocarbon generations in the depression has created the excellent basis for the formation of mediumtolarge scale fields in the high quality shallowwater deltaic facies offshore. Therefore, the shallow water deltaic reservoirs still should be the focus targets for exploration for adding new reserves and increasing productions in this region.
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