Research on the Sedimentation of Underwater Distributary Channels in Shallow Lacustrine Delta---Case Study of B19-4 Oilfield, Bohai Bay Basin

Based on the data of core observation, grain size analysis, micro paleontology, logging and well logging, the sedimentary environment and characteristics of NmIII and NmIV oil formation in the lower Minghuazhen Formation of B19-4 Oilfield are studied, and the formation reason of narrow strip sand body in this area is explained. The characteristics of formation thickness, lithology, paleontology and sedimentary microfacies indicate that the lower Minghuazhen Formation of B19-4 Oilfield belongs to the shallow water delta deposition of continental lake basin in the background of rising to falling from base level. The sedimentary environment is characterized by gentle slope, large accommodation space, weak hydrodynamic force, far-reaching sediment source, relatively stable structure, etc. the sedimentary sand body is dominated by distributary channel deposition, with developed natural dikes, and undeveloped mouth bars and crevasse fans. Because of this sedimentary environment, the underwater distributary channel of the shallow water delta is not easy to be changed, and the sand bodies of the underwater distributary channel of the multi-stage sedimentary cycles are vertically superposed, forming the sand bodies with narrow strip distribution.