Oil & Gas Geology ›› 2022, Vol. 43 ›› Issue (5): 1180-1193.doi: 10.11743/ogg20220514

• Petroleum Geology • Previous Articles     Next Articles

Lithofacies architecture of lacustrine fine-grained mixed reservoirs and its control over sweet spot: A case study of Permian Lucaogou Formation shale oil reservoir in the Jimsar Sag, Juggar Basin

Senlin Yin1(), Gongyang Chen1(), Changfu Xu2, Xianyue Xiong3, Jun Zhao2, Ke Hu2   

  1. 1.Institute of Mud Logging Technology and Engineering,Yangtze University,Jingzhou,Hubei 434023,China
    2.Xinjiang Oil Company,PetroChina,Karamay,Xinjiang 834000,China
    3.Coalbed Methane Company,PetroChina,Beijing 100028,China
  • Received:2021-11-05 Revised:2022-07-12 Online:2022-10-01 Published:2022-09-02
  • Contact: Gongyang Chen E-mail:yinxiang_love@qq.com;gychen8888@126.com

Abstract:

The lithofacies architecture of lacustrine fine-grained mixed silisiclastic-carbonate reservoirs is suggested to have certain control over the distribution of sweet spot of medium- to high-mature shale oil. But how exactly the mechanism works is still not clear. To tackle the issue, a case study is performed on the Permian Lucaogou Formation shale reservoir in the Jimsar Sag, Juggar Basin. Core and outcrop observation, logging data, lab test and production test are integrated to analyze the control of lithofacies architecture upon the distribution of sweet spots and its role in formulating development strategy. During the process, technologies including lithofacies architecture analysis, drone (or unmanned aerial vehicle) photography and 3D geologic modeling are used. The results show that combining the traditional outcrop observation measures with drone photography can be very useful in representing the lithofacies architecture features of the outcrops as the technology facilitates the well setting optimization, quantitative litho facies delineation with parameters, framework modeling and 3D lithofacies modeling. The lithofacies architecture patterns of this fine-grained mixed silisiclastic-carbonate reservoirs can be classified into three types, including the gradational, abrupt and special patterns. The gradational pattern, which usually indicates the occurrence of quality sweet spots, tends to be longitudinally symmetric and contains well-developed sandbodies mostly in a superimposition of multiple similar cycles with high quality source rocks and reservoirs with well-dissolved pores. The abrupt pattern hosts medium-developed sandbodies in an asymmetric architecture with a superimposition of several similar cycles. The source rocks are fine but reservoirs are thin. The special pattern is mostly thick clastic rocks with well-developed sandbodies in superimposed single cyrcles, which contain tight reservoirs and less fine sweet spots. The lithofacies architecture patterns control the distribution of sweet spots and shall be seriously considered during development planning for the formation. The gradational architecture pattern with well-developed sweet spots, is less heterogeneous and can be easily and economically tapped with pad drilling. The abrupt architecture pattern is the second-best choice due to their strong heterogeneity. The special architecture pattern features in scattered and discontinuous distribution of sweet spots as well as strong heterogeneity, thus is comparatively the worst development targets. A fine study of the spatial distribution of the lithofacies architecture may be needed before any development plan being drawn.

Key words: fine-grained mixed silisiclastic-carbonate rocks, lithofacies architecture, drone, sweet spot, shale oil, Lucaogou Formation, Jimsar Sag, Juggar Basin

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