Oil & Gas Geology ›› 2019, Vol. 40 ›› Issue (4): 917-929.doi: 10.11743/ogg20190419

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Characteristics and controlling factors of deep-water channel sedimentation in Lower Congo Basin, West Africa

Li Quan1,2, Wu Wei1,3, Kang Hongquan2, Ren Shijun4, Pang Lin'an2, Yang Ting2, Cai Lulu2, Liu Xiaolong2   

  1. 1. Institute of Resources and Environment, Henan Polytechnic University, Jiaozuo, Henan 454000, China;
    2. CNOOC Research Institute, Beijing 100102, China;
    3. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum(Beijing), Beijing 102249, China;
    4. NO.3 Extraction Factory, Qinghai Oil Field Company, PetroChina, Qinghai 816400, China
  • Received:2018-10-02 Revised:2019-01-22 Online:2019-08-28 Published:2019-06-01

Abstract: Deep-water channel system is an important part of the "Source-to-Sink" system from continental slope to deep-sea basin, and also a critical reservoir type in international deep-water petroleum exploration.The study of sedimentary characteristics, filling processes and controlling factors of the Miocene deep-water channels in Lower Congo Basin is of great help to deepen the understanding of basin dynamics and improve the prediction accuracy of deep-water reservoirs.Based on the integrated analysis of 3D seismic and logging data, we carried out in-depth study on the evolution of the Miocene high-resolution sequence stratigraphic framework, deep-water sedimentary units, types of deep-water channels, and the initiation, development, decline and extinction of channel complex systems, as well as the controlling factors in Lower Congo Basin.The technical means in terms of sequence stratigraphy, seismic stratigraphy and seismic geomorphology were resorted to in this study.The Miocene strata in the Lower Congo Basin can be divided into 14 fourth-order sequences with the maximum regression surface and the initial transgression surface serving as the sequence boundary.Among others, the fourth-order sequences SQ1L, SQ2L, SQ3L, SQ4L, SQ5L, SQ6L and SQ7L embody the major stages of deep-water channel development.Seven types of deep-water sedimentary units were identified, namely the erosional surface, channel filling, inner levee, outer levee, terminal lobe, pelagic deposit and slump block.And the channel filling and terminal lobe are arenaceous sedimentary units.The deep-water channels in the study area can be divided into four basic types, namely the single incised-channel, single aggradation channel, vertical aggradation channel complex and lateral migration channel complex.And the vertical aggradation and lateral migration channel complexes occur simultaneously in the fourth-order sequence SQ7L, indicating the controls of "autocyclicity" on channel filling processes.In conclusion, tectonic uplifting is a driving force for the formation of deep-water sand-rich channel systems, and the eustatic fluctuation in West Africa controls the development of third-order sequences and the scale of deep-water channel complex.The alternating climate change between greenhouse and icehouse controls the occurrence of deep-water arenaceous gravity flow deposits and deep-water argillaceous deposits in the fourth-order sequences.

Key words: gravity flow deposit, high-resolution sequence stratigraphic framework, sedimentary unit, deep-water channel, channel type, “Source-to-Sink&rdquo, System, controlling factor, Miocene, Lower Congo Basin

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