Pore structure and fractal characteristics of organic-rich shales: A case study of the lower Silurian Longmaxi shales in the Sichuan Basin,SW China |
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| Institution: | 1. Basin and Reservoir Research Center, China University of Petroleum, Beijing 102249, China;2. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China;3. Research Institute of Petroleum Exploration & Production, SINOPEC, Beijing 100083, China;4. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;1. Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, Canada;2. Trican Geological Solutions Ltd., Calgary, AB T2E 2M1, Canada;1. Key Laboratory of Tectonics and Petroleum Resources, Ministry of Education, China University of Geosciences, Wuhan 430074, China;2. Department of Earth and Environmental Sciences, The University of Texas at Arlington, Arlington, TX 76019, USA;3. School of Geosciences, China University of Petroleum, Qingdao, Shandong 266580, China;4. Exploration Company, SINOPEC, Chengdu 610064, China;5. Jianghan Oilfield Branch Company, SINOPEC, Qianjiang, Hubei 433124, China;6. School of Geosciences, Yangzte University, Wuhan, Hubei 430100, China;7. Petroleum Exploration and Development, Jianghan Oilfield Branch Company, SINOPEC, Wuhan, Hubei 430223, China;1. School of Energy Resources, China University of Geosciences, Beijing, 100083, PR China;2. Key Laboratory of Shale Gas Exploration and Evaluation, Ministry of Land and Resources, Beijing, 100083, PR China;3. Shanxi Yanchang Petroleum (Group) Corp. Ltd., 100083, Xi''an, 710075, PR China;4. Zhongyuan Oil Field 2nd Oil Factory of Sinopec, Puyang, 457532, PR China;5. Shandong Provincial Geo-mineral Engineering Exploration Institute, Jinan, 250014, PR China;1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China;2. Unconventional Natural Gas Research Institute, China University of Petroleum, Beijing 102249, China;3. College of Geosciences, China University of Petroleum, Beijing 102249, China;1. Key Laboratory of Tectonics and Petroleum Resources, Ministry of Education, China University of Geosciences, Wuhan 430074, China;2. Department of Earth and Environmental Sciences, The University of Texas at Arlington, Arlington, TX 76019, USA;3. Exploration Company, Sinopec, Chengdu 610064, China;4. Petroleum Exploration and Development, Jianghan Oilfield Branch Company, Sinopec, Wuhan 430223, China |
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| Abstract: | Shales from the Lower Silurian Longmaxi Formation in the Sichuan Basin are among the most important shale gas reservoirs in China, and have been investigated because of their great shale gas potential. To understand the pore structure and fractal characteristics of the shales, a series of experiments was conducted on core samples from the Lower Silurian Longmaxi Formation in the Sichuan Basin of China, including X-ray diffraction (XRD), total organic carbon (TOC) content and vitrinite reflectance (Ro) analysis, field emission-environmental scanning electron microscope (FE-ESEM) observation, and low-pressure N2 adsorption-desorption experiments. Frenkel-Halsey-Hill (FHH) method was applied to calculate fractal dimensions. In addition, the pore genesis, the relationships between composition and thermal maturity, the pore structure parameters, and the fractal dimensions are discussed. FE-ESEM observation results show that the Longmaxi Formation shales are dominated by organic-matter (OM) pores along with interparticle (interP) pores, intraparticle (intraP) pores and fracture pores. This study identified the fractal dimensions at relative pressures of 0–0.45 and 0.45–1 as D1 and D2 respectively. D1 ranged from 2.60 to 2.71 and D2 ranged from 2.71 to 2.82. D1 was typically smaller than D2, indicating that the smaller pores in shales were more homogeneous than the larger ones. The formation of these OM pores is owing to kerogen deformation during the thermal maturation, which results in a large number of nanopores. The pore structure of the Longmaxi Formation shales is primarily controlled by TOC content and thermal maturity. TOC content is a controlling factor on the fractal dimensions as it exhibited positive correlations with D1 and D2. Fractal dimensions are useful for the characterization of the pore structures complexity of the Longmaxi Formation shales because D1 and D2 correlate well with pore structure parameters as they both increase with the increase of surface area and the decrease of average pore diameter. |
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| Keywords: | Sichuan basin The Longmaxi shales Fractal dimension Pore structure FE-ESEM |
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