Shallow meandering river delta in the Huagang Formation in the southern Xihu Sag, East China Sea Basin

In response to the difficulties in studying the sedimentary facies of the H5 and H4 sand formations in the upper section of the Huagang Formation in the southern Xihu Sag of the East China Sea Basin, we established a new method and process for dividing facies zones in shallow water deltas, namely "single well facies determination - planar sand tracing - shoreline tracing - zoning and delineation" using seismic data and core data. Results shows that the study area had the geological background for the formation of shallow meandering river delta, in which a unique alternating sedimentary zone of different facies were formed. During the deposit period of the H5 and H4 sand groups, the terrain in the basin was wide and gentle, and water level changed frequently between flood season and dry season, resulting in the alternating deposits of delta plain facies and delta front facies in a short period in the central part of the study area. In the flood season, delta front and shallow lake sediments developed in the central part of the study area, while in dry season, delta plain developed. Under the guide of sedimentary model of shallow meandering river delta, many of river channel sand bodies were found in the central part of the study area. The channel sandstone bodies overlap on the large anticline structures, forming numerous litho-structural composite traps with great exploration potential. The research results were confirmed by new oil and gas discoveries.