Sedimentary control on the formation of a multi-superimposed gas system in the development of key layers in the sequence framework |
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| Institution: | 1. Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou 221008, China;2. School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China;3. School of Chemical Engineering, The University of Queensland, St. Lucia, Brisbane, QLD 4072, Australia;4. China United Coalbed Methane Corporation Limited, Beijing 100011, China;5. Xian Research Institute Company Limited, China Coal Technology and Engineering Group, Xian 710077, China;6. Xiamen Academy of Building Research Group Company Limited, Xiamen 361004, China;1. School of Geosciences, China University of Petroleum, Qingdao, 266580, China;2. Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, United States;3. Postdoctoral Scientic Research Working Station of Sinopec Shengli Oilfield Company, Dongying, 257000, China;4. Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204, United States;1. School of Resources and Earth Science, China University of Mining and Technology, Xuzhou, Jiangsu 221116, China;2. Key Laboratory of CBM Resources and Reservoir Formation Process of Ministry of Education, Xuzhou, Jiangsu 221116, China;3. Coalbed Methane and Shale Gas Engineering Research Center of Guizhou Province, Guiyang, Guizhou 550008, China;1. School of Energy Resource, China University of Geosciences (Beijing), 100083, China;2. Coal Reservoir Laboratory of National Engineering Research Center of CBM Development & Utilization, China University of Geosciences (Beijing), China;3. Beijing Key Laboratory of Unconventional Natural Gas Geological Evaluation and Development Engineering, China;4. Fundamental Experiment Center, China United Coalbed Methane National Engineering Research Center Co., Ltd, China;1. School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China;2. Key Lab of CBM Resources and Dynamic Accumulation Process, Ministry of Education of China, Xuzhou 221116, China;3. Geology Section of the Xi Shan Coal Electricity Group, Taiyuan 030053, China;1. College of Geoscience and Surveying Engineering, China University of Mining and Technology, Beijing, 100083, China;2. School of Energy Science and Engineering, Henan Polytechnic University, Jiaozuo, 454000, China;3. China United Coalbed Methane Corporation Limited, Beijing, 100016, China |
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| Abstract: | Based on core observations, well logs and test results of siderite-bearing mudstone from the Benxi Formation to the Member 2 of the Shanxi Formations in the Linxing block, northeastern Ordos Basin, a logging identification model for siderite-bearing mudstone (key layer) was established. The porosity characteristics and sealing property were quantitatively evaluated by logging data. Sedimentary control on the formation of multi-superimposed gas-bearing system in the development of key layers in the sequence framework was also discussed. The results showed that the siderite-bearing mudstone has obvious logging response characteristics, e.g., high photoelectric absorption cross-section index (PE), high density (DEN), high amplitude natural gamma ray (GR), low acoustic (AC), low resistivity (M2RX) and low neutron porosity (CNCF). The quantitatively evaluated results of the porosity characteristics and sealing property for the key layer showed that the key layer has the characteristics of low porosity (with an average of 1.20 percent), low permeability (with an average of 2.29 × 10?8μm2), and high breakthrough pressure (with an average of 12.32 MPa) in the study area. This layer acts as an impermeable gas barrier in a multi-superimposed gas system. The results also indicated that the material composition of the multi-superimposed gas-bearing system can be established by the sequence stratigraphic framework. The sedimentary evolution results in a cyclic rhythm of material composition vertically. The spatial distribution of the corresponding transgressive event layer near the maximum flooding surface (MFS) in the sequence framework restricts the spatial distribution of the key layer with high breakthrough pressure and low porosity, which constitutes the gas-bearing system boundary. The siderite-bearing mudstone formed near the MFS in the second-order sequence and constitutes a stable comparison of the first-order gas-bearing system boundary, which has a wide range of regional distribution and stable thickness. The siderite-bearing mudstone formed near the MFS in the third-order sequence is often incompletely preserved due to the late (underwater) diversion channel erosion and cutting. This layer forms the coal-bearing reservoirs, which we termed as a second-order gas-bearing system in adjacent third-order sequences to form a uniform gas-bearing system. |
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| Keywords: | Key layers Multi-superimposed gas system Sedimentary control Marine flooding surface Linxing block |
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