Oil & Gas Geology ›› 2022, Vol. 43 ›› Issue (4): 970-989.doi: 10.11743/ogg20220418

• Methods and Technologies • Previous Articles     Next Articles

Sedimentary characteristics and seismic sedimentologic responses of beach-bar deposits in a downfaulted lacustrine basin: A case study of Es1 in the Palaeogene Baxian Sag, Bohai Bay Basin

Zili Zhang1,2,3(), Qi Li2, Xiaomin Zhu3, Ruisheng Shi4, Shuanghui Xie3, Ruifeng Zhang5, Lanzhu Cao5   

  1. 1.Exploration and Development Research Institute of Southwest Oil and Gas Field Company,PetroChina,Chengdu,Sichuan 610051,China
    2.School of Ocean Sciences,China University of Geosciences (Beijing),Beijing 100083,China
    3.College of Geosciences,China University of Petroleum (Beijing),Beijing 102249,China
    4.Oilfield Production Department,China Oilfield Services Ltd. ,Tianjin 300459,China
    5.Huabei Oilfield Company,PetroChina,Renqiu,Hebei 062552,China
  • Received:2021-10-10 Revised:2022-05-08 Online:2022-07-14 Published:2022-07-14

Abstract:

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 1st member of Shahejie Formation (Es1) 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.

Key words: sedimentary model, seismic sedimentology, downfaulted lacustrine basin, beach-bar, the 1st member of Shahejie Formation (Es1), Palaeogene, Baxian Sag, Bohai Bay Basin

CLC Number: