Control of sequence stratigraphic evolution on the distribution and hydrocarbon accumulation of beach and bar reservoirs

Beach and bar sandstone reservoirs are widespread in the Paleogene faulted lake basins, Bohai Bay Basin, East China. There are many factors which control the generation and distribution of the beach and bar depositional system. This paper focuses on the control of sequence stratigraphic evolution on the formation, distribution and oil-gas accumulation of beach and bar reservoirs. The formation stage of beaches and bars is controlled by tectonic sequences. Beaches and bars are mainly formed in the early stage of the formation of second-order tectonic sequences and in the transitional period from fault to sag. They are the important component part of the transgressive systems tract of third-order sequences. Lake level fluctuation and sediment supply control the formation and composition of fourth-and fifth-cycles of beaches and bars. The depositional cyclicity of beach and bar is an important factor controlling the formation and distribution of reservoir and seal assemblage and the heterogeneity of beach and bar reservoirs. The flooding mudstone interval in the fourth-order cycle acts as local or regional seal and also controls the formation and development of reservoir-seal assemblage. Reservoir-seal assemblages vary in distribution and hydrocarbon potential.