Pore structure of the graptolite-derived OM in the Longmaxi Shale,southeastern Upper Yangtze Region,China |
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| Affiliation: | 1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum , Changping, Beijing 102249, China;2. Chongqing Institute of Geology and Mineral Resources, Chongqing 400042, China;3. CSIRO Earth Science and Resource Engineering, Private Bag 10, Clayton South, Victoria 3169, Australia;4. CSIRO Earth Science and Resource Engineering, P.O. Box 1130, Bentley, Western Australia 6102, Australia;1. Key Laboratory of Shale Gas Exploration and Evaluation, Ministry of Land and Resources, China University of Geosciences, Beijing 100083, China;2. School of Energy and Resources, China University of Geosciences, Beijing 100083, China;3. Key Laboratory of Tectonics and Petroleum Resources, Ministry of Education, China University of Geosciences, Wuhan 430074, China;4. PetroTECH Information Consulting Services Company, Beijing 100120, China;5. Henan Institute of Geological Survey, Henan 450000, China;1. Department Geochemistry of Petroleum and Coal, Federal Institute for Geosciences and Natural Resources, Stilleweg 2, D-30655 Hannover, Germany;2. Petrobras-Cenpes GEOQ/PDGEO, Rua Horácio Macedo no 950, Cidade Universitária-Ilha do Fundão, 21941-915 Rio de Janeiro, Brazil;3. Instituto Nacional del Carbón (INCAR-CSIC), PO Box 73, 33080 Oviedo, Spain;4. Instituto de Ciências da Terra (Pólo da Faculdade de Ciências UP), Departamento de Geociências, Ambiente e Ordenamento do Território da Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, 687 4169-007 Porto, Portugal;5. U.S. Geological Survey, MS 956 National Center, Reston, VA 20192, USA;6. Geological & Geophysical Institute of Hungary, Stefánia st. 14, Budapest 1143, Hungary;7. Department of Geology, University of Patras, GR-26504 Rio, Patras, Greece;8. Shell International Exploration and Production BV, Research and Technical Services, Volmerlaan 8, PO Box 60, 2280 AB Rijswijk, The Netherlands;9. University of Science and Technology (AGH), Al. Mickiewicza 30, 30-059 Kraków, Poland;10. Indiana Geological Survey, Indiana University, 611 North Walnut Grove, Bloomington, IN 47405-2208, USA;11. Laboratório de Palinofácies & Fácies Orgânica (LAFO), Departamento de Geologia (DEGL), Instituto de Geociências (IGEO), Universidade Federal do Rio de Janeiro (UFRJ), Brazil;12. Faculty of Earth Sciences, University of Silesia, Ul. Będzińska 60, 41-200 Sosnowiec, Poland;13. Polish Geological Institute-National Research Institute, Lower Silesian Branch, Al. Jaworowa 19, 53-122 Wrocław, Poland;14. Maersk Oil, Growth, Esplanaden 50, DK-1263 Copenhagen K, Denmark;15. Institute of Rock Structure and Mechanics, Academy of Sciences, V Holešovičkách 41, 18201 Praha, Czech Republic;p. Faculty of Mining and Geology, University of Belgrade, Djusina 7, 11000 Belgrade, Serbia |
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| Abstract: | The Lower Silurian Longmaxi Shale in the southeastern Upper Yangtze Region, which has been the main target for shale gas exploration and production in China, is black marine organic-rich shale and rich in graptolites. Graptolites, usually only periderms preserved in shales, are important organic component of the Longmaxi Shale. However, the pore structure of graptolite periderms and its contribution to gas storage has not yet been studied before. A combination of optical microscopy for identification and “mark” of graptolite and scanning electron microscope (SEM) for pore observations were conducted for the Longamxi Shale samples. Results show that pores are anisotropic developed in the Longmaxi graptolite periderms and greatly associated with their fine structure. Micrometer-sized fractures and spindle-shaped pores between cortical fibrils in the cortical bandage are greatly developed at section parallel to the bedding, while they are rare at section perpendicular to the bedding. Besides, numerous sapropel detritus rich in nanometer-sized pores are discretely distributed in the shale. Though graptolite periderms are low porosity from SEM image analysis, microfractures and elongated pores along the graptolite periderm wall may still make the graptolite an interconnected system. Together with the discrete porous sapropel detritus in shale, these graptolite-derived Organic Matter (OM) may form an interconnected organic pore system in the shale. The difference of pore development observed in graptolite periderms and sapropel detritus also give us new insight for the organic pore heterogeneity study. The OM composition, their fine structure and orientation in the rock may be important factors controlling OM pore development. The combination of identifying OM type under optical microscopy and pores observation under SEM for may be an effective method to study the OM pore development especially in shale that contain more OM. |
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| Keywords: | Graptolite-derived organic matter Pore structure Shale gas Longmaxi formation |
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