Paleogene lake deep water sedimentary facies in the northern zone of the Chezhen Sag, Bohai Bay Basin, China

This study researches an important genetic type of Paleogene sublacustrine fan deposits in widely developed glutenite bodies in the northern Chezhen Sag. The Paleogene sublacustrine fans in the Bohai Bay Basin are primarily distributed in Es3 (The third member of Paleogene Shahejie Formation). There are many sedimentary types in Chezhen depression, but understanding of the reservoir is too limited to support a development strategy. Therefore, a detailed study on the core characteristics, sedimentary structure, sedimentary microfacies and reservoir properties has been completed in order to reduce uncertainty. It is confirmed that the sublacustrine fan deposits are mostly characterized by a positive cycle of upward thinning, and the base is composed of conglomerate supporting conglomerate and massive gravel sandstone, which reflect the sedimentary characteristics of traction and gravity currents. Finally, the influence of sedimentary process on properties was assessed by establishing the correlation between microfacies and reservoir physical parameters, such as porosity, permeability, detrital particle. It is revealed that the sublacustrine fan glutenite body formed in the deep depression period is interspersed with deep- to semi-deep lake source rocks. The superior source–reservoir–caprock combination is one of the most important exploration targets in the northern zone.