Sedimentary evolution pattern influenced by sequence stratigraphy: a case study of the Nanpu Sag, Bohai Bay Basin, China

Abstract

Identifying and characterizing sedimentary evolution patterns are crucial for assessing the distributions of source and reservoir rocks, which are fundamental to hydrocarbon exploration. This study analyzed the stratigraphic sequence, lithological characteristics, sedimentary lithofacies, individual well sedimentary sequences, and seismic reflection properties. The analysis revealed six fourth-order sequences, including progradational and regressive sequences, indicative of water level changes. The sediment sources for the second and third sub-members of the Eocene Shahejie Formation's third member (Es32+3) in the Nanpu Sag were identified as the Baigezhuang and Xinanzhuang Uplifts. Predominantly, the sandstones are lithic arkose and feldspathic litharenite, both of which exhibit low compositional and structural maturity. Notably, 22 lithofacies and 8 lithofacies associations suggest fan delta processes. This study identified three fundamental seismic reflection package reflection types. These lithofacies associations, sedimentary sequences, and seismic reflections serve as critical indicators for determining sedimentary environments. The results from the sedimentary facies analysis indicate that the Es32+3 Formation developed fan delta deposits, controlled by the sequence of the sedimentary evolution pattern. The potential of these fan delta sediments to form oil and gas reservoirs is significant. Therefore, precise characterization of the sedimentary evolution pattern is essential for a comprehensive understanding of basin dynamics and hydrocarbon potential.