Special Oil & Gas Reservoirs ›› 2024, Vol. 31 ›› Issue (5): 31-40.DOI: 10.3969/j.issn.1006-6535.2024.05.004

• Geologic Exploration • Previous Articles     Next Articles

Microscopic Pore Structure Characteristics and Classification Evaluation of Tight Sandstone Gas Reservoirs in the Zhongba Area of Western Sichuan

Liu Lin1,2, Liu Xiangjun1,2, Sang Qin1,2, Xiong Jian1,2, Li Wei1,2, Liang Lixi1,2   

  1. 1. Geosciences and Technology,Southwest Petroleum University,Chengdu,Sichuan 610500,China;
    2. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu,Sichuan 610500,China
  • Received:2023-11-27 Revised:2024-06-25 Online:2024-10-25 Published:2024-12-24

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Abstract: The tight sandstone reservoirs in Zhongba Area of western Sichuan have experienced complex sedimentation and diagenesis evolution,resulting in poor reservoir physical properties,complex pore structure and strong heterogeneity,which makes it difficult to effectively evaluate the reservoir and to predict the"sweet spots".To address this issue,this study focused on the tight sandstone reservoirs of the Xujiahe Formation in the Zhongba Area,and systematically evaluated the microscopic pore structure characteristics of the reservoirs based on rock physics experiments including porosity and permeability from gas logging,casting thin sections,high-pressure mercury intrusion,and scanning electron microscope.Additionally,reservoir classification and well logging evaluation are conducted to determine the development and distribution characteristics of high-quality reservoirs with flow unit theory and BP neural network technology.The results show that the physical properties of the target reservoirs in the study area are poor,the reservoir space is mainly secondary intergranular pores and dissolution pores,the throat types are mainly point-like and necked,and the pore size is mainly nano-submicron.Reservoirs are classified into four types(Ⅰ-Ⅳ)based on flow unit.The Flow Zone Index (FZI) can effectively characterize the pore structure and flow characteristics of the reservoirs.Type Ⅱ and Ⅲ reservoirs are mainly developed in the second member of Xujiahe Formation in the study area,and type I reservoirs are developed in the ZB9-65-46 well field in the middle of the gas reservoir.The main structural reservoirs in the Zhongba Area are thick,predominantly type Ⅱ,while the reservoirs in the Laopingba and structural saddles are mostly thin layers,mainly type Ⅲ.Vertically,the effective reservoirs are primarily developed in the upper part of the second member of Xujiahe Formation,and its thickness accounts for 73.60% of the total reservoir thickness.The research results provide a scientific basis for reservoir evaluation and efficient development of similar tight sandstone gas reservoirs.

Key words: tight sandstone, pore structure, flow unit, reservoir evaluation, Xujiahe Formation

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