Oil & Gas Geology ›› 2020, Vol. 41 ›› Issue (6): 1129-1138.doi: 10.11743/ogg20200602

• Petroleum Geology • Previous Articles     Next Articles

Further understanding of differential accumulations of oil and water in tight sandstones with limited charging power:A case study of Chang 8 member in Huachi area, Ordos Basin, China

Zhenglu Xiao1,2(), Shijia Chen1,2,*(), Guanglin Liu3, Pan Wang4, Longxiang Tang2, Zhanghao Liu2   

  1. 1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China
    2. School of Geoscience and Technology, Southwest Petroleum University, Chengdu, Sichuan 610500, China
    3. Research Institute of Exploration and Development, PetroChina Changqing Oilfield Company, Xi'an, Shaanxi 710018, China
    4. No.1 Gas Production Plant, PetroChina Changqing Oilfield Company, Xi'an, Shaanxi 710018, China
  • Received:2018-05-11 Online:2020-12-28 Published:2020-12-09
  • Contact: Shijia Chen E-mail:154835727@qq.com;chensj1964@swpu.edu.cn

Abstract:

Batches of tight oil reservoirs including Jiyuan and Xifeng reservoirs were found in the 8th member of Yanchang Formation (Chang 8 member) in southwest Ordos Basin.Further exploration in the place reveals some areas with differential accumulations of oil and water such as Huachi and Chenghao areas.Nevertheless, the main controlling factors and distribution patterns of these accumulations are unknown.Based on a detailed discussion on source rock quality, source-reservoir contact relationship, sand body scale, physical properties and heterogeneity of reservoir in eastern and western Huachi area, this study explores the controlling factors and accumulation patterns of oil reservoirs in the differential areas.The results show that the pressure difference between source and reservoir is the main driving force of tight oil accumulations, but provides only limited charging power with backward migration.The factors controlling the differential accumulation of oil and water in eastern and western Huachi area are the argillaceous barriers grown between source and reservoir, sand body size and reservoir heterogeneity, of which, the argillaceous barriers control the downward migration of crude oil, the size of sand body serves as the lateral sealing for crude oil, and the reservoir heterogeneity determines the differential accumulation of crude oil in a single sand body.Given the limited charging power, reservoirs that are large in scale, good in physical properties and strong in homogeneity, are not ideal harbors for oil to accumulate.On the contrary, reservoirs that are small in scale, poor in physical properties and strong in heterogeneity, are more readily to provide lithological or physical barriers to stop the escape of oil.This understanding, quite different from the previous viewpoint that "high-quality sands indicate good oil traps", may serve to shed light on the further exploration in the differential areas of the Ordos Basin.

Key words: main controlling factor, differential accumulation, tight oil, Chang 8 member, Ordos Basin

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