Oil & Gas Geology ›› 2021, Vol. 42 ›› Issue (6): 1440-1450.doi: 10.11743/ogg20210618

• Petroleum Geology • Previous Articles     Next Articles

Depositional characteristics of locally restricted channel complex in deep water and its influence on reservoir properties: A case study of the Eocene series, Rovuma Basin

Hui Sun(), Guozhang Fan, Dali Shao, Guoping Zuo, Shaozhi Liu, Hongping Wang, Hongxia Ma, Xiaoyong Xu, Yintao Lu, Chun Yan   

  1. Hangzhou Research Institute of Geology, PetroChina, Hangzhou, Zhejiang 310023, China
  • Received:2021-04-16 Online:2021-12-28 Published:2021-12-16

Abstract:

The Eocene channel sandstone reservoirs in the Rovuma Basin, East Africa, are of deep sea gravity flow deposits. The Eocene channel complex is characterized by unilateral migration and multi-level erosion and filling. Research methods and technologies including core observation, well logging analysis, and 3D seismic attribute analysis, etc., are applied to study the channel complex. The relationship between the sedimentary facies of channel complex and its grade is clarified. The Eocene channel complex of locally restricted type can be divided into 3 subfacies, 3 grades and 4 sedimentary periods; moreover, the evolutionary process of the 4 periods is described, and the impact of sedimentary unit type, sedimentary period of the channel complex and the distance from the channel mouth on the reservoir properties is analyzed. The Eocene channel complex in the Rovuma Basin is composed of 3 sedimentary subfacies, i.e. complex substrate, main deposits of confined filling and overflow wedge. Channel filling deposition includes 3 grades of channel complex, composite channel and channel. Under the influence of bottom current, a north-to-south migration occurs within a single composite channel and between composite channels of different stages from old to young; and thereby the reservoir is mainly of the superimposing channel facies in laterally continuous distribution. On the other hand, the reservoir properties of the Eocene channel complex of local restriction type are closely associated with the sedimentary period, the type of sedimentary units and the distance from the channel mouth. Sandstone reservoirs are mainly developed in superimposing and meandering channels, and the superimposing channel facies is the most favorable to reservoir development. The earlier the channel deposition occurs, the thicker a single sandstone layer will be; however, the later the channel deposition begins, the better the physical properties of a reservoir will be, and the closer to the channel mouth, the greater the reservoir thickness and the lower the porosity will be. The variation of shale content and permeability with extension distance is complicated. In a nutshell, the research results serve for deepening the study of sedimentary reservoir of deep-water channel complex facies, as well as are of practical value to establishing geological models in the early stage of oil/gas field development.

Key words: composite channel, channel complex, deep-water deposits, reservoir characteristics, Eocene, Rovuma Basin

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