陆相断陷湖盆滩坝沉积特征与地震沉积学响应

Sedimentary characteristics and seismic sedimentologic responses of beach-bar deposits in a downfaulted lacustrine basin： A case study of E in the Palaeogene Baxian Sag， Bohai Bay Basin

张自力 李琦 朱筱敏 施瑞生 谢爽慧 张锐锋 曹兰柱

Zili Zhang Qi Li Xiaomin Zhu Ruisheng Shi Shuanghui Xie Ruifeng Zhang Lanzhu Cao

随着油气勘探程度的提高，滩坝作为陆相湖盆重要的储集体类型在隐蔽油气勘探中逐渐得到重视。以渤海湾盆地霸县凹陷沙河街组一段为研究目标，立足于岩心、钻井岩-电响应特征确定滩坝的类型及组合，利用三维地震资料综合解释并基于地震沉积学原理，明确不同成因类型滩坝的空间分布。结果表明，研究区滩坝岩性以（钙质）细砂岩、粉砂岩、生物灰岩、白云岩及泥质灰岩为主。依据岩性组合将滩坝划分为碎屑岩滩坝、碳酸盐岩滩坝、混积滩坝及风暴滩坝4种类型，并建立相应的滩坝沉积模式。其中，碎屑岩滩坝是三角洲前缘砂体改造、再堆积的结果，碳酸盐岩滩坝为低物源供给背景下湖盆内碳酸盐原生沉淀的产物，混积滩坝是陆源碎屑与内源碳酸盐岩碎屑混积的产物，风暴滩坝的形成则与湖浪对早期滩坝的破坏作用有关。滩坝时空分布具有继承性特征，垂向上从湖侵体系域至高位体系域沉积时期碎屑岩滩坝—混积滩坝—碳酸盐岩滩坝—混积滩坝—碎屑岩滩坝依次叠置，平面上古湖盆内断层翘倾盘及古底形凸起区是滩坝的重要发育部位，马西走滑断层末端形成的局部挤压隆起是大规模碳酸盐岩滩坝及混积滩坝集中发育区。滩坝的类型及发育特征记录了断陷湖盆构造-层序演化信息，是沉积盆地形成早期古地理格局及演化过程的物质表现。通过对滩坝的精细解剖，有助于恢复盆地的早期演化过程，为下一步储层预测和油气勘探开发提供参考。

With the increasing of exploration maturity， beach-bar deposit， as an important reservoir type in downfaulted lacustrine basins， has drawn more attention in search of subtle oil/gas reservoirs. The analysis of the core， lithology， and electrical properties serves to determine the type and combination of beach-bars in the 1 member of Shahejie Formation （E） in the Baxian Sag， Bohai Bay Basin. The spatial distribution of these beach-bars of diverse genetic types is then clarified by a comprehensive interpretation of 3D seismic data and based on the principle of seismic sedimentology. The results show that the lithologic types of the beach-bars in the study area mainly include （calcareous） fine-grained sandstone， siltstone， biolimestone， dolomite and argillaceous limestone. According to lithologic combinations， the beach-bars can be classified into four types， that is， clastic rock type， carbonate rock type， mixed carbonate-silisiclastic rock type and tempestite type， the depositional models of which are established respectively. Among others， the beach-bar of clastic rock type is a product of reformation and re-accumulation of delta-front sand bodies； the beach-bar of carbonate rock type is a product of primary deposition of carbonate rocks in the lacustrine basin under low provenance supply capacity； the beach-bar of mixed carbonate-silisiclastic rock type is a product of mixed deposition of terrigenous clastics and intrabasinal carbonate； and the beach-bar of tempestite type is developed under the destructive effect of waves on early formed beach-bars. The temporal and spatial distribution of beach bars show the feature of inheritance. Vertically， beach-bars of clastic rock type， of mixed carbonate-silisiclastic rock type， of carbonate rock type， of mixed carbonate-silisiclastic rock type and of clastic rock type are deposited and superimposed successively from lake transgressive systems tract to highstand systems tract. While in map view， beach-bars are mainly developed on the tilted fault walls and salients of paleo-lakebed form in the paleo-lake basin. Beach-bars of carbonate rock and mixed carbonate-silisiclastic rock type are seen in large scale in local uplifts caused by compression at the end of Maxi strike-slip fault. In all， the types and development characteristics of beach-bars serve to record the tectono-stratigraphic sequence evolution of the downfaulted lacustrine basin and as the material manifestation of paleogeographic pattern and its evolutionary process in the early stage of rifting. The fine description of beach-bars is conducive to restoring the early evolutionary process of the basin， so as to be of referential value to reservoir prediction and oil/gas exploration and development in the future.

10.11743/ogg20220418