Neogene Shallow Water Deltaic System and Large Hydrocarbon Accumulations in Bohai Bay,China

Bohai basin is characterized by tectonically-uniform block with steady and slow subsidence, which resulted in low-relief, low gradient, and high-stand lake-level depositional settings during the Neogene. Excellent reservoir-seal 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 reservoir-seal combinations. Shallow water deltaic facies are positioned near the prolific hydrocarbon-enriched 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 medium-to-large scale fields in the high quality shallow-water 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.