Heterogeneous nanoporosity of the Silurian Longmaxi Formation shale gas reservoir in the Sichuan Basin using the QEMSCAN,FIB-SEM,and nano-CT methods |
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| Institution: | 1. School of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, China;2. Key Laboratory of Shale Gas Exploration and Evaluation, Ministry of Land and Resources, Beijing 100083, China;3. School of Geosciences, China University of Petroleum (East China), Qingdao 266580, China;1. Key Laboratory of Tectonics and Petroleum Resources (China University of Geosciences), Ministry of Education, Wuhan 430074, PR China;2. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum (Beijing), #18, Fuxue Rd, Changping, Beijing 102249, PR China;3. Ministry of Education Key Laboratory of Petroleum Engineering, China University of Petroleum (Beijing), #18, Fuxue Rd, Changping, Beijing 102249, PR China;4. Energy and Mineral Resources Group (EMR), Institute of Geology and Geochemistry of Petroleum and Coal, Lochnerstr. 4–20, RWTH Aachen University, 52056 Aachen, Germany |
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| Abstract: | Nanoporosity of a shale gas reservoir provides essential information on the gas accumulation space and controls the gas reserves. The characteristics of heterogeneous nanoporosity of four shale samples are analyzed by combining quantitative evaluation of minerals by scanning electronic microscopy (QEMSCAN), focused ion beam-scanning electron microscopy (FIB-SEM), and nano-CT. The representative elementary area (REA) is proposed by QEMSCAN to detect the imaging area that can represent the overall contents of minerals and organic matter. Combined with the statistics of pores in minerals and organic matter by FIB-SEM, the quantitative nanoporosity is obtained. The nano-CT is used to compare the total nanoporosity that was obtained by FIB-SEM. The results show that shale has distinct characteristics in nanoporosities due to the variation in organic matter and mineral content. The major pore sizes of the organic matter and clay minerals are smaller than 400 nanometers (nm), and the pore sizes of feldspar and pyrite are mainly 200–600 nm. The pore sizes for pores developed in quartz and carbonate minerals range from a few nanometers to 1000 nm. Furthermore, pores smaller than 400 nm mainly provide the total nanoporosity. The nanoporosities in the organic matter are approximately 17%–21%. Since the organic matter content (0.54%–6.98%) is low, the organic matter contributes approximately 5%–33% of the total nanoporosity in shale. Conversely, the nanoporosities in quartz and clay are generally lower than 3%. Since the mineral content (93.02%–99.46%) is obviously higher than the organic matter content, the minerals contribute approximately 67%–95% of the total nanoporosity in shale. |
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| Keywords: | Nanoporosity Organic pore Mineral pore Pore size distribution Shale gas reservoir |
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