Abstract: Ⅱ-Ⅴ oil groups are the main oil layers in the lower part of Minghuazhen Formation(N₁m^L) in Oilfiled A, Bohai. By observation and analysis of the characteristics of sedimentological structure, rock and ore, particle size in core, well logging types, geophysical attributes characteristics,the sedimentary environments mainly include meandering river and shallow water delta. The meandering river mainly develops 4 kinds of sedimentary microfacies, which are channel, splay, natural levee and flood plain. But the shallow water delta mainly develops 4 kinds of sedimentary microfacies, which are underwater distributary channel, the underwater natural levee, the mouth bar and interdistributary in oil field range. Through the analysis of the characteristics of sedimentary facies, combined with high resolution sequence stratigraphy, and discussed the vertical evolution characteristics of Ⅱ-Ⅴ oil groups in the lower part of N₁m^L in Oilfiled A, Bohai, we find that meandering river of Ⅴoil group in a long period of ascending half cycle has the characteristic of strip distribution, and shallow water delta distributes a lump taye in the plane, and the internal sandbody has a poor connection, which is developed in Ⅳ oil group in the early stage of a long period of descending half cycle. The shallow water delta distributes a lobate taye in the plane, sand lateral stack, which is developed in Ⅲ oil group in the middle stage of a long period of descending half cycle. The shallow water delta distributes a bird-foot taye in the plane, sand vertical stack, which is developed inⅡoil group in the last stage of a long period of descending half cycle. Finally, it puts forward the model of sedimentary evolution of the oil field.

Key words: Bohai oilfiled, N₁m^L, Meandering River, shallow water delta, sedimentary evolution model