A Novel Method to Obtain Permeability in a Dual-Pore System Using Geophysical Logs: A Case Study of an Upper Triassic Formation,Southwest Ordos Basin,China |
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Authors: | Qin Zhen Wu Dong Luo Shaocheng Ma Xiugang Huang Ke Tian Fei Xiao Kun Chen Xiao Hou Min Pan Heping |
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Institution: | 1.Engineering Research Center of Nuclear Technology Application (East China Institute of Technology), Ministry of Education, Nanchang, 330013, China ;2.State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, 610059, China ;3.Key Laboratory of Tectonics and Petroleum Resources (China University of Geosciences), Ministry of Education, Wuhan, 430074, China ;4.International Logging Company, CNPC Greatwall Drilling Company, Beijing, 100101, China ;5.China Petroleum Logging Co. Ltd., Xi’an, 710077, Shaanxi, China ;6.Logging Company of China Petrochemical Corporation North China Petroleum Bureau, Zhengzhou, 450000, China ;7.Institute of Geophysics & Geomatics, China University of Geosciences, Wuhan, 430074, China ; |
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Abstract: |
Fractured tight sandstone reservoirs are dual-pore systems including matrix pores and natural fractures, which both contribute to the system permeability. However, most previous studies either calculated the matrix permeability or obtained the fracture permeability to represent the system permeability in the logging evaluation of fractured tight sandstones because existing logging methods cannot distinguish the two types. In this study, a novel method is proposed to estimate the system permeability in fractured tight sandstones using geophysical logs. First, the fracture characteristics in the Upper Triassic Chang 8 member of the Yanchang Formation, southwest Ordos Basin, China, were analyzed. Based on the hydraulic flow unit approach, the formation classification criteria and the corresponding permeability–porosity models were established; then, the pure matrix permeability in the dual-pore system was calculated using geophysical logs. Based on the fracture characteristics, the relative pure fracture permeability was obtained using the Sibbit and Faivre method. By applying the Parsons’ model in boreholes, the system permeability was then calculated by coupling the relationship between the two permeabilities. Finally, two field applications in the study area demonstrate the feasibility of the proposed method, and the logging responses, application effects and applicable conditions of this method are discussed in detail. These applications indicate that the proposed method is suitable for tight reservoirs with fracture widths less than 200 μm, and considered to be dual-pore systems. |
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