This paper focuses on the tight marlstone reservoir in lower 3

rd

Member of the Shahejie Formation in central and southern Shulu sag

Bohai Bay Basin.The reservoir is of great economic potential

and has the same characteristics as tight oil reservoir

such as reservoir-source coexisting

continuous distribution

oil-bearing but unclear boundary.Owing to its tight physical property and complex sedimentary environment

it is challenging to precisely predict distribution of the marlstone reservoir.In this paper

we presented a comprehensive geophysical workflow for prediction of tight marlstone reservoir.Firstly

the geological and geophysical features of the reservoir are studied.Secondly

multiple wells correlation and well-to-seismic calibration are carried out.Thereafter seismic-based sequential stratigraphy frameworks are established

and depositional units are identified.Then qualitative interpretation for the target reservoir is carried out by using techniques including geophysical modeling

basic seismic attributes analysis and post-stack impedance inversion.Finally

spatial and temporal reservoir distribution is analyzed with the integration of strata slicing technique

seismic attributes analysis and sequential boundary constraints.The results show that the lower 3

rd

Member of Shahejie Formation can be considered as a complete third-order sequence

and the distribution range of the target reservoir becomes wider as the depositional stages changes from low system tract

to transgressive system tract and finally to high system tract.The reservoir is thickest in central sag

while it is relatively pure and the most extensive in late stage of transgressive system tract.The inner slope has well-developed faults with NEE strike

and interbedded conglomerate and marlstone

thus is a favorable area for further exploration.