Abstract: The Neogene Lower Member of the Minghuazhen Formation in K Oilfield of the Bohai Sea is controlled by delta sedimentation in shallow waters, and the internal structures of the resulting composite sandbodies are highly complex. A Sand Body of the Lower Member of the Minghuazhen Formation was used as an example for determining the genesis, periods of sedimentation, and single-period distribution characteristics of composite sandbodies. The stratigraphic structure of composite sandbodies was constructed according to stratigraphic divisions, and the genesis of sandbodies was determined through a combination of well-logging and rock core data under the guidance of depositional models. Through well-seismic ties, the temporal periods of these causes were differentiated, and the distribution characteristics of single sandbodies in each of these periods were characterized. The results indicate that A Sand Body was formed by distributary channels, natural levees, terminal crevasse splays, and interdistributary bays, which may be further subdivided into three periods of sedimentation. The contact relationships of sandbodies in each of these periods may be categorized into four types according to their genetics as lateral splits in distributary channels, interchannel natural levee sedimentation, interchannel-interdistributary bay sedimentation and distributary channel-terminal crevasse splay contact.

Key words: Bohai Bay Basin, K Oilfield, Minghuazhen Formation, composite sandbodies, internal genesis