Geomorphology of channel sandbodies in fluvially dominated shallow water delta front: taking the Lower Member of the Minghuazhen Formation in BZ34 Oilfield of the Huanghekou Sag, Bohai Bay Basin as an example

The Lower Member of the Neogene Minghuazhen Formation (N₁m^l) is the main oil-bearing sand body unit in the BZ34 Oilfield in Huanghekou Sag, Bohai Bay Basin, North China, in which delta front deposits in fluvially dominated shallow waters were developed. To better characterize the structural characteristics and distribution of the front sand bodies, taking the second oil unit of N₁m^l as an example, the sedimentary types, geomorphological structures, and depositional models of the sand body were analyzed based on the data from coring, seismic profiling, and logging. Results show that the sand bodies are dominated by underwater distributary channels in shallow water delta front. According to the logging curves and overlapping of the sand bodies, four channel types were recognized: massive incised river channel, layered overlapping channel, layered isolated channel, and finger-shaped isolated channel. The distribution and genesis of the sand bodies were affected mainly by paleotopography, sediment supply rate, base level cycle, and paleoclimate. The underwater distributary channel deposits in the BZ34 Oil Field are characteristic of incisive superposition in vertical direction and meandering patchy distribution in horizontal, which is similar to the modern case of fluvially dominated shallow water delta channels in Poyang Lake, South China. This study provided a guidance for infill adjustment and potential tapping in later stage for the remaining oil in BZ34 Oilfield.