高精度层序约束下三角洲-滩坝沉积体系精细刻画与岩性圈闭分布规律

Fine characterization and lithologic trap distribution patterns of delta-beach bar sedimentary system under high-precision sequence constraints： A case study of the upper submember of the 4 member of the Shahejie Formation in the eastern segment of the southern gentle slope of Dongying Sag， Jiyang Depression， Bohai Bay Basin

刘成龙 王艳忠 杨怀宇 操应长 王淑萍 郭超凡 郭豪 陈兆祥 宋林坤 黄歆媛

Chenglong LIU Yanzhong WANG Huaiyu YANG Yingchang CAO Shuping WANG Chaofan GUO Hao GUO Zhaoxiang CHEN Linkun SONG Xinyuan HUANG

为研究断陷盆地斜坡带低位体系域岩性圈闭发育，以渤海湾盆地济阳坳陷东营凹陷南坡东段沙河街组四段上亚段（沙四上亚段）低位体系域为研究对象，利用岩心、测录井资料，开展了高精度层序划分对比、层序动态演化和沉积微相平面精细刻画研究。研究表明：沙四上亚段低位体系域划分为3个准层序组、9个准层序，发育6种准层序、4种准层序组以及5种体系域地层叠加样式，经历9次准层序级别相对湖平面升降，在相对湖平面下降期物源供给充足，平面上由盆缘进积为主型向盆内进积型过渡分布。主要发育三角洲-滩坝沉积体系，包括扇三角洲、三角洲和滩坝3种沉积相以及7种沉积微相类型。东营凹陷南坡东段沙四上亚段低位体系域内部以坝主体和滩脊微相尖灭砂体为储集体，以准层序和准层序组底部湖侵泥岩为局部盖层、水进体系域泥岩为区域盖层，形成岩性圈闭。

The study aims at revealing the development of lithologic traps in the lowstand systems tract （LST） in the slope zone in a downfaulted basin， and investigates the LST in the upper submember of the 4 member of the Shahejie Formation （the Sha 4 Member） in the eastern segment of the southern gentle slope zone of the Dongying Sag， Jiyang Depression， in the Bohai Bay Basin （the study area）. Using data from cores and logs， we examine the high-precision division， comparison， and dynamic evolution of sequences and perform the fine characterization of sedimentary microfacies in the planar view. The results indicate that the LST in the upper submember of the Sha 4 Member can be divided into three parasequence sets composed of nine parasequences， presenting six， four， and five stratigraphic superposition patterns at the parasequence， parasequence set， and systems tract levels， respectively. The LST in the study area experienced nine relative lake-level fluctuations at the parasequence level， receiving sufficient sediment supply during the relative lake level falls. This led to a planar distribution characterized by predominant basin-margin progradation transitioning to intrabasinal progradation. The LST contains a delta-beach bar sedimentary system comprising three sedimentary facies， namely the fan delta， delta， and beach bar facies， which can be further divided into seven sedimentary microfacies. Lithologic traps have been formed within the LST， with sand bodies pinching out in beach bars’ main bodies and beach ridge microfacies as reservoirs， mudstones formed by lacustrine transgression at the bottom of parasequences and parasequence sets as local seals， and mudstones in the transgressive systems tract （TST） as regional seals.

10.11743/ogg20240416