Sequence stratigraphy and reservoir potential in the Wenan inner-slope of the Baxian sag, Bohai Bay Basin, eastern China

The high-resolution sequences, depositional environments, and lithostratigraphic trapping styles of an Eocene lacustrine rift succession in the Wenan inner-slope of the Baxian sag in Jizhong depression of Bohai Bay Basin were studied using newly processed pre-stack seismic 3-D data, complemented by well logs and cores of new drilled well XL1. Four third-order sequences were identified in the study interval (the 3rd and 4th members of the Shahejie Formation). The lower two sequences mainly contain transgressive system tracts (TST) and highstand system tracts (HST), whereas the upper sequence only contains lowstand system tracts (LST). Seismic stratal slices demonstrate that the deltaic deposits were widely developed in the Wenan inner-slope. AVO inversion showed that the net sandstone of the study stratigraphic units decreased in thickness in the depositional-dip-oriented direction. A new potential reservoir model of the 4th member of the Shahejie Formation was built for the development of abundant undiscovered lithostratigraphic reserves and four major lithostratigraphic trapping styles were identified.