Abstract: The third Member of the Dongying Formation (Ed 3) in the LD16 oilfield in the Bohai Bay Basin is the main target for oil and gas exploration. Following the study of comparison of well and seismic and sequence stratigraphy, integrated analyses on paleogeomorphology, core facies, well-logging facies, seismic facies, and amplitude attribute slices were conducted based on 3-D seismic, well-logging, and core data to clarify the sedimentary facies, distribution and evolution. Using the classic theory Vail sequence stratigraphy, we recognized one third-order sequence stratigraphic unit within the Ed3, which can be divided into lowstand system tract (LST), transgressive system tract (TST) and highstand system tract (HST). During the LST and TST stages, the Liaoxi Uplift was subject to an intense erosion due to the exposure. Fan delta and gravity flow deposit systems were well developed along of sufficient sedimentary supply. The sand bodies of fan delta are mainly medium- and fine-grained sandstones with well-developed sedimentary structures of lag deposits, wavy bedding, and bioturbation. During the HST stage, the Liaoxi Uplift was submerged, and the capacity of the sedimentary supply was weakened. Therefore, braided river delta front and gravity flow deposit systems were developed in the study area. The subaqueous distributary channels of braided river delta consist of medium-fine-grained sandstone with wedge cross-bedding. The gravity flow deposits are mainly slump-induced sub-lacustrine fan deposits with deformed structures and sandy-debris flow deposits, which show sandstones with floating pebbles and mud clasts. The depositional evolution is closely related to the paleo-geomorphic evolution in the study area. In addition, fault systems control the distribution of sand bodies. The gravity flow sand bodies commonly developed in the front of the fault slope-break zone. The research on sedimentary facies, distribution and evolution is helpful for further hydrocarbon exploration in the study area.

Key words: sequence stratigraphy, sedimentary system, seismic sedimentology, third Member of the Dongying Formation, LD16 oilfield