关键词: 辫状河三角洲, 沉积学, 地震沉积学, 沙三上亚段, 莱州湾凹陷

Abstract: The upper Member 3 of the Shahejie Formation (E2s3U) in the KenLi (KL) Oilfield is the primary target strata for medium-deep oil and gas exploration in Laizhouwan Sag, Bohai Bay Basin. Integrating the analyses of sedimentary background, three-dimensional seismic, core, and well-logging data, using the seismic sedimentological technique, we studied on sedimentary characteristics and depositional evolution of the braided river delta formed during the E2s3U interval in KenLi Oilfield. The results show that braided river deltas developed in the study area received sediments from three source areas, namely Laibei Low Uplift, Kendong Uplift, and Weibei Low Uplift. The well-sorted sand bodies in the delta plain were mainly fine-medium sandstone; whereas the sand bodies in the delta front were fine sandstone and siltstone. Sedimentary structures were developed well under tractive currents. Additionally, wavy bedding and bioturbation structures are common, suggesting turbulent water conditions in the delta front environment. The oblique progradation reflections were developed along the source direction, and multi-unit mounded-shape seismic reflections were observed across the source direction. Comprehensive analyses of paleo-geomorphology, sedimentary characteristics, and amplitude attribute slices of strata reveal that the Laibei Low Uplift is the dominant source area, which provided abundant sediments to the depositional area. Middle and eastern districts of the sedimentary area were central depositional regions, where a large area of braided river delta deposits (95~130 km2) with landward-stepping was developed. Western and eastern districts of the sedimentary area were fed by multi source areas. The delta front from the Kendong Uplift gradually shrank, and the delta front from the Weibei Uplift gradually prograded basinward. Study on the sedimentary characteristics and evolution of depositional processes of the braided river delta systems will serve as a reference for reservoir prediction and oil exploration and development.

Key words: braided river delta, sedimentology, seismic sedimentology, upper Member 3 of the Shahejie Formation, Laizhouwan Sag