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Volume 31 Issue 1
Jan.  2020
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Zixuan Liu, Detian Yan, Xing Niu. Insights into Pore Structure and Fractal Characteristics of the Lower Cambrian Niutitang Formation Shale on the Yangtze Platform, South China. Journal of Earth Science, 2020, 31(1): 169-180. doi: 10.1007/s12583-020-1259-0
Citation: Zixuan Liu, Detian Yan, Xing Niu. Insights into Pore Structure and Fractal Characteristics of the Lower Cambrian Niutitang Formation Shale on the Yangtze Platform, South China. Journal of Earth Science, 2020, 31(1): 169-180. doi: 10.1007/s12583-020-1259-0

Insights into Pore Structure and Fractal Characteristics of the Lower Cambrian Niutitang Formation Shale on the Yangtze Platform, South China

doi: 10.1007/s12583-020-1259-0
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  • Shales from the Lower Cambrian Niutitang Formation of Yangtze Platform have been widely investigated due to its shale gas potential. To better illustrate the pore structure and fractal characteristics of shale, a series of experiments were conducted on outcrop samples from the Lower Cambrian Niutitang Formation on Yangtze Platform, including X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and low-temperature nitrogen adsorption. Frenkel-Halsey-Hill (FHH) model was adopted to calculate the fractal dimensions. Furthermore, the relationships between fractal dimensions and pore structure parameters and mineral composition are discussed. FE-SEM observation results show that interparticle pores are most developed in shale, followed by intraparticle pores. This study identified the fractal dimensions D1 (ranging from 2.558 0 to 2.710 2) and D2 (ranging from 2.541 5 to 2.765 2). The pore structure of the Niutitang Formation shale is primarily controlled by quartz and clay content. Fractal dimensions are able to characterize the pore structure complexity of Niutitang Formation shale because D1 and D2 correlate well with average pore diameter and quartz content.
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  • Bankole, S. A., Buckman, J., Stow, D., et al., 2019. Automated Image Analysis of Mud and Mudrock Microstructure and Characteristics of Hemipelagic Sediments: IODP Expedition 339. Journal of Earth Science, 30(2): 407–421. https://doi.org/10.1007/s12583-019-1210-4 doi:  10.1007/s12583-019-1210-4
    Bertier, P., Schweinar, K., Stanjek, H., et al., 2016. On the Use and Abuse of N2 Physisorption for the Characterisation of the Pore Structure of Shales. Cms Workshop Lectures, 21: 151–161. https://doi.org/10.1346/cms-wls-21.12 doi:  10.1346/cms-wls-21.12
    Chalmers, G. R., Bustin, R. M., Power, I. M., 2012. Characterization of Gas Shale Pore Systems by Porosimetry, Pycnometry, Surface Area, and Field Emission Scanning Electron Microscopy/transmission Electron Microscopy Image Analyses: Examples from the Barnett, Woodford, Haynesville, Marcellus, and Doig Units. AAPG Bulletin, 96(6): 1099–1119. https://doi.org/10.1306/10171111052 doi:  10.1306/10171111052
    Chang, S., Feng, Q. L., Zhang, L., 2018. New Siliceous Microfossils from the Terreneuvian Yanjiahe Formation, South China: The Possible Earliest Radiolarian Fossil Record. Journal of Earth Science, 29(4): 912–919. https://doi.org/10.1007/s12583-017-0960-0 doi:  10.1007/s12583-017-0960-0
    Chen, L., Lu, Y. C., Jiang, S., et al., 2015. Heterogeneity of the Lower Silurian Longmaxi Marine Shale in the Southeast Sichuan Basin of China. Marine and Petroleum Geology, 65: 232–246. https://doi.org/10.1016/j.marpetgeo.2015.04.003 doi:  10.1016/j.marpetgeo.2015.04.003
    Chen, Q., Zhang, J. C., Tang, X., et al., 2016. Relationship between Pore Type and Pore Size of Marine Shale: An Example from the Sinian– Cambrian Formation, Upper Yangtze Region, South China. International Journal of Coal Geology, 158: 13–28. https://doi.org/10.1016/j.coal.2016.03.001 doi:  10.1016/j.coal.2016.03.001
    Chen, Y. Y., Mastalerz, M., Schimmelmann, A., 2014. Heterogeneity of Shale Documented by Micro-FTIR and Image Analysis. Journal of Microscopy, 256(3): 177–189. https://doi.org/10.1111/jmi.12169 doi:  10.1111/jmi.12169
    Clarkson, C. R., Solano, N., Bustin, R. M., et al., 2013. Pore Structure Characterization of North American Shale Gas Reservoirs Using USANS/SANS, Gas Adsorption, and Mercury Intrusion. Fuel, 103: 606–616. https://doi.org/10.1016/j.fuel.2012.06.119 doi:  10.1016/j.fuel.2012.06.119
    Curtis, M. E., Cardott, B. J., Sondergeld, C. H., et al., 2012. Development of Organic Porosity in the Woodford Shale with Increasing Thermal Maturity. International Journal of Coal Geology, 103: 26–31. https://doi.org/10.1016/j.coal.2012.08.004 doi:  10.1016/j.coal.2012.08.004
    Fu, H. J., Tang, D. Z., Xu, T., et al., 2017. Characteristics of Pore Structure and Fractal Dimension of Low-Rank Coal: A Case Study of Lower Jurassic Xishanyao Coal in the Southern Junggar Basin, NW China. Fuel, 193: 254–264. https://doi.org/10.1016/j.fuel.2016.11.069 doi:  10.1016/j.fuel.2016.11.069
    Gregg, S. J., Sing, K. S. W., 1982. Adsorption, Surface Area and Porosity: 2nd Ed.. Academic Press, London
    Guo, Q. J., Strauss, H., Zhu, M. Y., et al., 2013. High Resolution Organic Carbon Isotope Stratigraphy from a Slope to Basinal Setting on the Yangtze Platform, South China: Implications for the Ediacaran– Cambrian Transition. Precambrian Research, 225: 209–217. https://doi.org/10.1016/j.precamres.2011.10.003 doi:  10.1016/j.precamres.2011.10.003
    Hazra, B., Wood, D. A., Vishal, V., et al., 2018. Porosity Controls and Fractal Disposition of Organic-Rich Permian Shales Using Low-Pressure Adsorption Techniques. Fuel, 220: 837–848. https://doi.org/10.1016/j.fuel.2018.02.023 doi:  10.1016/j.fuel.2018.02.023
    Hu, J. G., Tang, S. H., Zhang, S. H., 2016. Investigation of Pore Structure and Fractal Characteristics of the Lower Silurian Longmaxi Shales in Western Hunan and Hubei Provinces in China. Journal of Natural Gas Science and Engineering, 28: 522–535. https://doi.org/10.1016/j.jngse.2015.12.024 doi:  10.1016/j.jngse.2015.12.024
    Li, A., Ding, W. L., He, J. H., et al., 2016. Investigation of Pore Structure and Fractal Characteristics of Organic-Rich Shale Reservoirs: A Case Study of Lower Cambrian Qiongzhusi Formation in Malong Block of Eastern Yunnan Province, South China. Marine and Petroleum Geology, 70: 46–57. https://doi.org/10.1016/j.marpetgeo.2015.11.004 doi:  10.1016/j.marpetgeo.2015.11.004
    Li, J. Q., Zhang, P. F., Lu, S. F., et al., 2018. Scale-Dependent Nature of Porosity and Pore Size Distribution in Lacustrine Shales: An Investigation by BIB-SEM and X-Ray CT Methods. Journal of Earth Science, 30(4): 823–833. https://doi.org/10.1007/s12583-018-0835-z doi:  10.1007/s12583-018-0835-z
    Li, Y., Wang, Z. S., Pan, Z. J., et al., 2019. Pore Structure and Its Fractal Dimensions of Transitional Shale: A Cross-Section from East Margin of the Ordos Basin, China. Fuel, 241: 417–431. https://doi.org/10.1016/j.fuel.2018.12.066 doi:  10.1016/j.fuel.2018.12.066
    Li, Z. Q., Shen, X., Qi, Z. Y., et al., 2018. Study on the Pore Structure and Fractal Characteristics of Marine and Continental Shale Based on Mercury Porosimetry, N2 Adsorption and NMR Methods. Journal of Natural Gas Science and Engineering, 53: 12–21. https://doi.org/10.1016/j.jngse.2018.02.027 doi:  10.1016/j.jngse.2018.02.027
    Liang, C., Jiang, Z. X., Cao, Y. C., et al., 2017. Sedimentary Characteristics and Paleoenvironment of Shale in the Wufeng-Longmaxi Formation, North Guizhou Province, and Its Shale Gas Potential. Journal of Earth Science, 28(6): 1020–1031. https://doi.org/10.1007/s12583-016-0932-x doi:  10.1007/s12583-016-0932-x
    Liang, L. X., Xiong, J., Liu, X. J., 2015. An Investigation of the Fractal Characteristics of the Upper Ordovician Wufeng Formation Shale Using Nitrogen Adsorption Analysis. Journal of Natural Gas Science and Engineering, 27: 402–409. https://doi.org/10.1016/j.jngse.2015.07.023 doi:  10.1016/j.jngse.2015.07.023
    Liu, X. F., Song, D. Z., He, X. Q., et al., 2019. Nanopore Structure of Deep-Burial Coals Explored by AFM. Fuel, 246: 9–17. https://doi.org/10.1016/j.fuel.2019.02.090 doi:  10.1016/j.fuel.2019.02.090
    Liu, X. J., Xiong, J., Liang, L. X., 2015. Investigation of Pore Structure and Fractal Characteristics of Organic-Rich Yanchang Formation Shale in Central China by Nitrogen Adsorption/Desorption Analysis. Journal of Natural Gas Science and Engineering, 22: 62–72. https://doi.org/10.1016/j.jngse.2014.11.020 doi:  10.1016/j.jngse.2014.11.020
    Loucks, R. G., Reed, R. M., Ruppel, S. C., et al., 2009. Morphology, Genesis, and Distribution of Nanometer-Scale Pores in Siliceous Mudstones of the Mississippian Barnett Shale. Journal of Sedimentary Research, 79(12): 848–861. https://doi.org/10.2110/jsr.2009.092 doi:  10.2110/jsr.2009.092
    Loucks, R. G., Reed, R. M., Ruppel, S. C., et al., 2012. Spectrum of Pore Types and Networks in Mudrocks and a Descriptive Classification for Matrix-Related Mudrock Pores. AAPG Bulletin, 96(6): 1071–1098. https://doi.org/10.1306/08171111061 doi:  10.1306/08171111061
    Loucks, R. G., Ruppel, S. C., 2007. Mississippian Barnett Shale: Lithofacies and Depositional Setting of a Deep-Water Shale-Gas Succession in the Fort Worth Basin, Texas. AAPG Bulletin, 91(4): 579–601. https://doi.org/10.1306/11020606059 doi:  10.1306/11020606059
    Lü, D. W., Wang, D. D., Li, Z. X., et al., 2017. Depositional Environment, Sequence Stratigraphy and Sedimentary Mineralization Mechanism in the Coal Bed- and Oil Shale-Bearing Succession: A Case from the Paleogene Huangxian Basin of China. Journal of Petroleum Science and Engineering, 148: 32–51. https://doi.org/10.1016/j.petrol.2016.09.028 doi:  10.1016/j.petrol.2016.09.028
    Mandelbrot, B. B., 1975. Les Objects Fractals: Form, Hasard et Dimension. Flammarion, Paris
    Nelson, P. H., 2009. Pore-Throat Sizes in Sandstones, Tight Sandstones, and Shales. AAPG Bulletin, 93(3): 329–340. https://doi.org/10.1306/10240808059 doi:  10.1306/10240808059
    Niu, X., Yan, D. T., Zhuang, X. G., et al., 2018. Origin of Quartz in the Lower Cambrian Niutitang Formation in South Hubei Province, Upper Yangtze Platform. Marine and Petroleum Geology, 96: 271–287. https://doi.org/10.1016/j.marpetgeo.2018.06.005 doi:  10.1016/j.marpetgeo.2018.06.005
    Pfeifer, P., Avnir, D., 1983. Chemistry in Noninteger Dimensions between Two and Three. I. Fractal Theory of Heterogeneous Surfaces. The Journal of Chemical Physics, 79(7): 3558–3565. https://doi.org/10.1063/1.446210 doi:  10.1063/1.446210
    Pyun, S. I., Rhee, C. K., 2004. An Investigation of Fractal Characteristics of Mesoporous Carbon Electrodes with Various Pore Structures. Electrochimica Acta, 49(24): 4171–4180. https://doi.org/10.1016/j.electacta.2004.04.012 doi:  10.1016/j.electacta.2004.04.012
    Shao, X. H., Pang, X. Q., Li, Q. W., et al., 2017. Pore Structure and Fractal Characteristics of Organic-Rich Shales: A Case Study of the Lower Silurian Longmaxi Shales in the Sichuan Basin, SW China. Marine and Petroleum Geology, 80: 192–202. https://doi.org/10.1016/j.marpetgeo.2016.11.025 doi:  10.1016/j.marpetgeo.2016.11.025
    Sing, K. S. W., Everett, D. H., Haul, R. A. W., et al., 1985. Reporting Physisorption Data for Gas/Solid Systems with Special Reference to the Determination of Surface Area and Porosity. Pure and Applied Chemistry, 57(4): 603–619. https://doi.org/10.1351/pac198557040603 doi:  10.1351/pac198557040603
    Steele, W. A., 1983. Adsorption Surface Area and Porosity. Journal of Colloid and Interface Science, 94(2): 597–598. https://doi.org/10.1016/0021-9797(83)90305-3 doi:  10.1016/0021-9797(83)90305-3
    Steiner, M., Li, G. X., Qian, Y., et al., 2007. Neoproterozoic to Early Cambrian Small Shelly Fossil Assemblages and a Revised Biostratigraphic Correlation of the Yangtze Platform (China). Palaeogeography, Palaeoclimatology, Palaeoecology, 254(1/2): 67–99. https://doi.org/10.1016/j.palaeo.2007.03.046 doi:  10.1016/j.palaeo.2007.03.046
    Sun, M. D., Yu, B. S., Hu, Q. H., et al., 2017. Pore Characteristics of Longmaxi Shale Gas Reservoir in the Northwest of Guizhou, China: Investigations Using Small-Angle Neutron Scattering (SANS), Helium Pycnometry, and Gas Sorption Isotherm. International Journal of Coal Geology, 171: 61–68. https://doi.org/10.1016/j.coal.2016.12.004 doi:  10.1016/j.coal.2016.12.004
    Sun, W., Zuo, Y. J., Wu, Z. H., et al., 2019. Fractal Analysis of Pores and the Pore Structure of the Lower Cambrian Niutitang Shale in Northern Guizhou Province: Investigations Using NMR, SEM and Image Analyses. Marine and Petroleum Geology, 99: 416–428. https://doi.org/10.1016/j.marpetgeo.2018.10.042 doi:  10.1016/j.marpetgeo.2018.10.042
    Sun, Y. F., Zhao, Y. X., Yuan, L., 2018. Quantifying Nano-Pore Heterogeneity and Anisotropy in Gas Shale by Synchrotron Radiation Nano-CT. Microporous and Mesoporous Materials, 258: 8–16. https://doi.org/10.1016/j.micromeso.2017.08.049 doi:  10.1016/j.micromeso.2017.08.049
    Tang, X. L., Jiang, Z. X., Huang, H. X., et al., 2016. Lithofacies Characteristics and Its Effect on Gas Storage of the Silurian Longmaxi Marine Shale in the Southeast Sichuan Basin, China. Journal of Natural Gas Science and Engineering, 28: 338–346. https://doi.org/10.1016/j.jngse.2015.12.026 doi:  10.1016/j.jngse.2015.12.026
    Tang, X. L., Jiang, Z. X., Li, Z., et al., 2015. The Effect of the Variation in Material Composition on the Heterogeneous Pore Structure of High-Maturity Shale of the Silurian Longmaxi Formation in the Southeastern Sichuan Basin, China. Journal of Natural Gas Science and Engineering, 23: 464–473. https://doi.org/10.1016/j.jngse.2015.02.031 doi:  10.1016/j.jngse.2015.02.031
    Wang, H. J., Wu, W., Chen, T., et al., 2019. Pore Structure and Fractal Analysis of Shale Oil Reservoirs: A Case Study of the Paleogene Shahejie Formation in the Dongying Depression, Bohai Bay, China. Journal of Petroleum Science and Engineering, 177: 711–723. https://doi.org/10.1016/j.petrol.2019.02.081 doi:  10.1016/j.petrol.2019.02.081
    Wang, H. Z., Mo, X. X., 1995. An Outline of the Tectonic Evolution of China. Episodes, 18(1/2): 6–16. https://doi.org/10.18814/epiiugs/1995/v18i1.2/003 doi:  10.18814/epiiugs/1995/v18i1.2/003
    Wang, J. B., Bao, H. Y., Lu, Y. Q., et al., 2019. Quantitative Characterization and Main Controlling Factors of Shale Gas Occurrence in Jiaoshiba Area, Fuling. Earth Science, 44(3): 1001–1011. https://doi.org/10.3799/dqkx.2018.388 (in Chinese with English Abstract) doi:  10.3799/dqkx.2018.388
    Wang, J., Li, Z., 2003. History of Neoproterozoic Rift Basins in South China: Implications for Rodinia Break-Up. Precambrian Research, 122(1/2/3/4): 141–158. https://doi.org/10.1016/s0301-9268(02)00209-7 doi:  10.1016/s0301-9268(02)00209-7
    Wang, P. F., Jiang, Z. X., Yin, L. S., et al., 2017. Lithofacies Classification and Its Effect on Pore Structure of the Cambrian Marine Shale in the Upper Yangtze Platform, South China: Evidence from FE-SEM and Gas Adsorption Analysis. Journal of Petroleum Science and Engineering, 156: 307–321. https://doi.org/10.1016/j.petrol.2017.06.011 doi:  10.1016/j.petrol.2017.06.011
    Wang, Y., Zhu, Y. M., Liu, S. M., et al., 2016. Pore Characterization and Its Impact on Methane Adsorption Capacity for Organic-Rich Marine Shales. Fuel, 181: 227–237. https://doi.org/10.1016/j.fuel.2016.04.082 doi:  10.1016/j.fuel.2016.04.082
    Wei, X. F., Liu, R. B., Zhang, T. S., et al., 2013. Micro-Pores Structure Characteristics and Development Control Factors of Shale Gas Reservoir: A Case of Longmaxi Formation in XX Area of Southern Sichan and Northern Guizhou. Natural Gas Geoscience, 4(5): 1048–1059 (in Chinese with English Abstract)
    Wu, C. J., Tuo, J. C., Zhang, L. F., et al., 2017. Pore Characteristics Differences between Clay-Rich and Clay-Poor Shales of the Lower Cambrian Niutitang Formation in the Northern Guizhou Area, and Insights into Shale Gas Storage Mechanisms. International Journal of Coal Geology, 178: 13–25. https://doi.org/10.1016/j.coal.2017.04.009 doi:  10.1016/j.coal.2017.04.009
    Xu, H., Zhou, W., Zhang, R., et al., 2019. Characterizations of Pore, Mineral and Petrographic Properties of Marine Shale Using Multiple Techniques and Their Implications on Gas Storage Capability for Sichuan Longmaxi Gas Shale Field in China. Fuel, 241: 360–371. https://doi.org/10.1016/j.fuel.2018.12.035 doi:  10.1016/j.fuel.2018.12.035
    Yang, F., Ning, Z. F., Wang, Q., et al., 2016. Pore Structure of Cambrian Shales from the Sichuan Basin in China and Implications to Gas Storage. Marine and Petroleum Geology, 70: 14–26. https://doi.org/10.1016/j.marpetgeo.2015.11.001 doi:  10.1016/j.marpetgeo.2015.11.001
    Yang, X. Q., Fan, T. L., Wu, Y., 2016. Lithofacies and Cyclicity of the Lower Cambrian Niutitang Shale in the Mayang Basin of Western Hunan, South China. Journal of Natural Gas Science and Engineering, 28: 74–86. https://doi.org/10.1016/j.jngse.2015.11.007 doi:  10.1016/j.jngse.2015.11.007
    Yao, Y. B., Liu, D. M., Tang, D. Z., et al., 2008. Fractal Characterization of Adsorption-Pores of Coals from North China: An Investigation on CH4 Adsorption Capacity of Coals. International Journal of Coal Geology, 73(1): 27–42. https://doi.org/10.1016/j.coal.2007.07.003 doi:  10.1016/j.coal.2007.07.003
    Zeng, W. T., Zhang, J. C., Ding, W. L., et al., 2014. The Gas Content of Continental Yanchang Shale and It Main Controlling Factors: A Case Study of Liuping-171 Well in Ordos Basin. Natural Gas Geoscience, 25(2): 291–301. https://doi.org/10.11764/j.issn.1672-1926.2014.02.0291 (in Chinese with English Abstract) doi:  10.11764/j.issn.1672-1926.2014.02.0291
    Zhang, S. L., Yan, J. P., Hu, Q. H., et al., 2019. Integrated NMR and FE-SEM Methods for Pore Structure Characterization of Shahejie Shale from the Dongying Depression, Bohai Bay Basin. Marine and Petroleum Geology, 100: 85–94. https://doi.org/10.1016/j.marpetgeo.2018.11.003 doi:  10.1016/j.marpetgeo.2018.11.003
    Zhou, L., Kang, Z. H., 2016. Fractal Characterization of Pores in Shales Using NMR: A Case Study from the Lower Cambrian Niutitang Formation in the Middle Yangtze Platform, Southwest China. Journal of Natural Gas Science and Engineering, 35: 860–872. https://doi.org/10.1016/j.jngse.2016.09.030 doi:  10.1016/j.jngse.2016.09.030
    Zhu, R. K., Jin, X., Wang, X. Q., et al., 2018. Multi-Scale Digital Rock Evaluation on Complex Reservoir. Earth Science, 43(5): 1773–1782. https://doi.org/10.3799/dqkx.2018.429 (in Chinese with English Abstract) doi:  10.3799/dqkx.2018.429
    Zou, C. N., Zhu, R. K., Bai, B, et al., 2011. First Discovery of Nano-Pore Throat in Oil and Gas Reservoir in China and Its Scientific Value. Acta Petrologica Sinica, 27(6): 1857–1864. https://doi.org/10.1007/s12250-011-3157-6 (in Chinese with English Abstract) doi:  10.1007/s12250-011-3157-6
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Insights into Pore Structure and Fractal Characteristics of the Lower Cambrian Niutitang Formation Shale on the Yangtze Platform, South China

doi: 10.1007/s12583-020-1259-0
    Corresponding author: Detian Yan

Abstract: Shales from the Lower Cambrian Niutitang Formation of Yangtze Platform have been widely investigated due to its shale gas potential. To better illustrate the pore structure and fractal characteristics of shale, a series of experiments were conducted on outcrop samples from the Lower Cambrian Niutitang Formation on Yangtze Platform, including X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and low-temperature nitrogen adsorption. Frenkel-Halsey-Hill (FHH) model was adopted to calculate the fractal dimensions. Furthermore, the relationships between fractal dimensions and pore structure parameters and mineral composition are discussed. FE-SEM observation results show that interparticle pores are most developed in shale, followed by intraparticle pores. This study identified the fractal dimensions D1 (ranging from 2.558 0 to 2.710 2) and D2 (ranging from 2.541 5 to 2.765 2). The pore structure of the Niutitang Formation shale is primarily controlled by quartz and clay content. Fractal dimensions are able to characterize the pore structure complexity of Niutitang Formation shale because D1 and D2 correlate well with average pore diameter and quartz content.

Zixuan Liu, Detian Yan, Xing Niu. Insights into Pore Structure and Fractal Characteristics of the Lower Cambrian Niutitang Formation Shale on the Yangtze Platform, South China. Journal of Earth Science, 2020, 31(1): 169-180. doi: 10.1007/s12583-020-1259-0
Citation: Zixuan Liu, Detian Yan, Xing Niu. Insights into Pore Structure and Fractal Characteristics of the Lower Cambrian Niutitang Formation Shale on the Yangtze Platform, South China. Journal of Earth Science, 2020, 31(1): 169-180. doi: 10.1007/s12583-020-1259-0
  • As an unconventional resource, shale gas has become increasingly important for gas exploration due to the demand for global energy and advancement in theory and technology (Clarkson, 2013). The heterogeneity of shale reservoir is reflected in many aspects, such as sedimentary structure, lithofacies, mineralogy and geochemistry and they have a vital influence on pore structure (Liang et al., 2017; Tang et al., 2016, 2015; Chen L et al., 2015; Chen Y Y et al., 2014). Different from conventional gas reservoir, shale displays a rather complicated pore structure with nanometer to micrometer pores (Bankole et al., 2019; Nelson, 2009). More importantly, the pore structure controls the shale gas storage and diffusion capability, existing forms and transport mechanisms (Lü et al., 2017; Wang et al., 2016). The pore structure can be described via parameters such as pore types, pore size, pore surface area, pore volume and spatial distribution (Curtis et al., 2012; Loucks et al., 2009, 2007) with various methods to characterize pore structure properties. The first type is ray detection, including field emission electron microscopy (FE-SEM), focused ion beam electron microscopy (FIB-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), nano CT, nuclear magnetic resonance (NMR), small angle and ultra- small angle neutron scattering techniques (SANS/USANS) (Liu et al., 2019; Sun W et al., 2019; Chang et al., 2018; Li J Q et al., 2018; Sun Y F et al., 2018; Zhu et al., 2018; Shao et al., 2017; Sun M D et al., 2017; Chen et al., 2016; Zhou and Kang, 2016; Zou et al., 2011). The second type is fluid intrusion, including low-temperature N2 adsorption, low-pressure CO2 adsorption and high pressure mercury injection (Li Y et al., 2019; Wang et al., 2019; Fu et al., 2017; Hu et al., 2016; Li A et al., 2016). Nevertheless, these methods are confined to directly describe the complexity and heterogeneity of shale microstructures due to the fact that pores are unevenly distributed in a three-dimensional space (Li et al., 2016). Mandelbrot (1975) put forward the fractal theory to quantify the irregularity degree and statistical self-similarity of complex objects that don't obey Euclidean geometry. What's more, a fractal dimension which is between 2 and 3 is applied to quantify the irregularity and self-similarity. Pfeifer and Avnir (1983) first reported the fractal features of reservoir pore structure. Nowadays, it has been widely used to elucidate shale and coal pore structures and proves to be an effective method to describe the geometry of pores with irregular surface and space structure (Sun et al., 2019; Wang H J et al., 2019; Zhang et al., 2019; Li Z Q et al., 2018). Low-temperature N2 adsorption, high-pressure mercury intrusion, and NMR have been used to study the fractal features of pores, among which N2 adsorption combined with Frenkel-Halsey-Hill (FHH) model is widely used for calculation of fractal dimension (Hazra et al., 2018; Hu et al., 2016; Zhou et al., 2016; Liang et al., 2015; Liu et al., 2015). However, there are still some questions to be answered. The calculation method of fractal dimensions, the dominating factors on pore fractal features and pore types classifications according to SEM are in hot discussion. This paper aims at the pore structure features of the Lower Cambrian Niutitang Formation shale in western Hubei Province, China. Low-temperature N2 adsorption experiment was utilized to gain pore structure parameters. Four types of pores were observed by FE-SEM, and two fractal dimensions were calculated based on FHH model and N2 adsorption data. Furthermore, the relationships between fractal dimensions and shale mineral composition, pore structure parameters were discussed. The combination of qualitative observation and quantitative tests of shale pores offers a better understanding of Niutitang shale.

  • The Yangtze Platform has undergone a long history of deformation and amalgamation and presents a complex tectono- stratigraphic framework of passive margin basins (Wang and Mo, 1995). From Late pre-Cambrian Ediacaran to the Ordovician Period, thick sandstone, carbonate, and shale deposited in the Yangtze Craton in the passive margin of Yangtze Platform (Wang and Li, 2003). In the Early Cambrian, the sedimentary facies of Yangtze Block can be divided into (1) the carbonate platform, (2) the transition belt, (3) deep water deposit of Nanhua Basin from northwest to southeast (Fig. 1; Niu et al., 2018; Guo et al., 2013; Steiner et al., 2007).

    The Gucheng Village Section locates in Hefeng County, southeastern of Hubei Province. Palaeogeographically, the section is located in the carbonate platform (Niu et al., 2018). In outcrops, Niutitang Formation develops (1) black siliceous shale and argillaceous shale of lower member, (2) crystalline limestone of middle member, and (3) dark grey calcilutite and black shale with thin-medium bedding of upper member (Niu et al., 2018). According to previous studies, the mineral composition of Niutitang Formation shale is dominated by quartz and clay minerals (Wu et al., 2017; Yang X Q et al., 2016).

  • Nine shale samples of Niutitang Formation were collected from Gucheng Village, Hefeng County. These samples are distributed among the lower part of the Niutitang Formation in the studied profile and were unweathered. All samples were carefully prepared before conducting a series of experiments. X-ray diffraction (XRD) analysis, field-emission scanning electron microscopy (FE-SEM) observation and low-temperature N2 adsorption experiment were conducted to gain mineral composition, pore morphology, pore structure parameters, and fractal dimensions.

    The total organic carbon (TOC) content was measured using the LECO CS230 carbon and sulfur analyzer (Shao et al., 2017). The powdered samples were pre-treated with 5% hydrochloric acid solution at 80 ℃ to remove inorganic carbon, and washed with pure water and centrifuged several times until there was no residual hydrochloric acid solution, which can be tested by pH paper. Finally, the samples were dried, and the 2 mg powder was put into the instrument to measure TOC content.

    Figure 1.  Paleogeographic map of South China Craton in Early Cambrian and lithological column of target formation.

    X-ray diffraction (XRD) experiment was conducted on pulverized samples with X'Pert PRO DY2198 Diffractometer. The mineral composition was calculated semi-quantitatively, according to the peak area of the individual mineral on the X-ray spectra.

    The FEI Quanta 450 FEG-SEM equipped with an energy- dispersive spectrometer (EDS) was utilized to get micropores images. Before observation, two samples (G-02 and G-09) were prepared by Ar ion milling. The SEM imaging was carried out at 24 ℃ and with the humidity level at 35%.

    Low-temperature N2 adsorption experiment was performed on Micromeritics ASAP 2020 Surface Area and Porosity Analyzer to represent mesopore characteristics. Before analyzation, samples were crushed into 60–80 meshes powder, de-watered in a drying oven at 110 ℃ for 4 h and degassed under vacuum at 70 ℃ for 12 h. Then N2 adsorption-desorption isotherms were gained at -195 ℃. Pore surface area was calculated at the relative pressure range of 0.06–0.2 based on Brunauer Emmette Teller (BET) method, and pore volume was calculated through Barrette Joynere Halenda (BJH) method (Steele, 1983).

  • The shale mineral compositions are presented in Table 1. The XRD results reflect differences in the mineral compositions of the over-matured Niutitang Formation shale which is mainly composed of quartz and clay minerals. Based on the content of siliceous minerals, clay minerals, and carbonate minerals, Niutitang Formation shale can be divided into two lithofacies: siliceous shale and argillaceous shale (Fig. 2; Niu et al., 2018; Wang et al., 2017). The quartz content ranges from 25 wt.% to 56 wt.% averaging at 34 wt.% (Fig. 3b), whereas clay minerals content varies from 31 wt.% to 64 wt.% averaging at 52 wt.%. Clay minerals are composed of chlorite (with an average content of 10.7 wt.%) (Fig. 3c) and illite (with an average content of 41.3 wt.%) (Fig. 3e). Besides, there are albite (the average content is 12.8 wt.%) (Fig. 3e) and a small amount of pyrite (Fig. 3j) and siderite. The TOC content ranges from 0.90 wt.% to 1.33 wt.% with an average of 1.09 wt.%.

    Sample TOC Q Ab Ill Chl Py Sd
    G-01 1.29 56 12 28 3 0 1
    G-02 1.33 45 11 35 6 3 0
    G-03 1.15 25 17 40 17 1 0
    G-04 0.98 27 11 48 12 0 2
    G-05 0.90 36 14 47 1 1 1
    G-06 1.00 26 9 45 19 1 0
    G-07 1.10 34 15 47 4 0 0
    G-08 1.04 27 14 40 18 1 0
    G-09 1.01 28 12 42 17 1 0
    TOC. Total organic carbon; Q. quartz; Ab. albite; Ill. illite; Chl. chlorite; Py. pyrite; Sd. siderite.

    Table 1.  Mineral compositions (wt.%) and TOC (wt.%) content of Niutitang Formation shale

    Figure 2.  Lithofacies classification of Niutitang Formation shale.

    Figure 3.  Four types of pores observed in the Lower Cambrian Niutitang Formation. (a) Organic matter pores near the pyrite; (b) organic matter strip; (c) interparticle pores between albite and chlorite and between albite particles; (d) interparticle pores between quartz and albite and intraparticle pores inside quartz; (e) intraparticle pores inside albite and illite; interparticle pores between albite and illite; (f) interparticle pores between orthoclase and albite; (g) interparticle pores between quartz; (h) and (i) intraparticle pores inside chlorite; (j) intraparticle pores inside pyrite framboid; (k) micro-fractures along the albite; (l) micro- fractures inside clay mineral. Ab. Albite; Chl. chlorite; Ill. illite; Kf. orthoclase; Py. pyrite.

  • Shale pore space is essential for hydrocarbon migration and reservoir space analysis, and numerous studies on pore morphology have been done using the FE-SEM method (Li et al., 2019; Sun et al., 2019; Xu et al., 2019; Zhang et al., 2019). According to FE-SEM observation, the pores of Niutitang Formation shale are at nano-scale to micron scale on the whole. Based on pores morphology, four types of pores are observed: organic matter (OM) pores, interparticle (InterP) pores, intraparticle (IntraP) pores and micro-fractures (Loucks et al., 2012). Among them, InterP pores are most developed, followed by IntraP pores. The OM pores are seldom developed and isolated in the studied shale samples, not while as commonly seen in Niutitang Formation shale in other area (Sun et al., 2019; Yang F et al., 2016). They usually show the bubble-like shape and develop near the pyrite (Fig. 3a), and there is also an elongated organic strip where OM pores are seldom developed (Fig. 3b). InterP pores are often observed between different mineral particles and their shapes in the study area are mainly angular. The width of InterP pores ranges from dozens of nanometers up to several micrometers depending on the size of the neighboring mineral grains. There are triangle pores between albite particles, plate-like pores between albite particles, or between albite and chlorite (Fig. 3c). Also, stylolite-like pores between albite and quartz (Fig. 3d), slit-like pores between albite and illite (Fig. 3e), triangle pores between quartz and orthoclase, albite and orthoclase (Fig. 3f) and irregular pores between quartz particles (Fig. 3g) can be observed. IntraP pores are pores developed inside mineral particles, and intercrystalline pore is included. Clay minerals make up about 50% in studied shale samples, and abundant pores inside clay minerals are observed. Linear pores often locate along cleavage sheet of illite (Fig. 3e), and sometimes they are bent (Fig. 3g). Besides, there are pores in quartz (Fig. 3d) and albite (Fig. 3e). Intercrystalline pores can often be observed inside pyrite (Fig. 3j), and their shapes are more regular. The pyrite framboid is surrounded by clay minerals, and its diameter is less than 10 μm. As for micro-fractures, they can extend almost 60 μm and present along rigid minerals such as albite (Fig. 3k) and cut through the clay minerals (Fig. 3l).

  • Low-temperature N2 adsorption is mainly used to analyze the pore volumes and surface area distributions of mesopores when the relative pressure (P/P0) was between 0.01 and 1. At relatively low pressure range (P/P0 < 0.45), the adsorbed quantity increases slowly, representing monolayer adsorption dominated by van der Waals' force. When relative pressure is between 0.45 and 0.8, the adsorbed quantity increases significantly, indicating multilayer adsorption. The adsorption curve and desorption curve depart at the relative pressure of 0.45, and the hysteresis loop begins to develop, which is related to capillary condensation taking place in mesopores (Gregg and Sing, 1982). At higher relative pressure (0.8 < P/P0 < 1.0), the adsorbed quantity increases sharply, but there's a limiting uptake over a range of high P/P0 (Fig. 4). For the studied samples, the isotherm shapes belong to type Ⅳ according to IUPAC classification (Sing et al., 1985), manifesting a continuous pore system from dominating micropore and mesopore to a few macropores.

    Figure 4.  N2 adsorption-desorption isotherms of 9 samples from the Niutitang Formation shales.

    Hysteresis appearing in the multilayer range of physisorption isotherms is usually associated with capillary condensation in mesopore structure. The shapes of hysteresis loops have been identified with different pore structures (Sing et al., 1985). For the studied Niutitang Formation shale, the hysteresis loops belong to type H3, indicating the aggregates of plate-like particles giving rise to slit-shaped pores (Fig. 4) (Sing et al., 1985), which is reflected in Figs. 3e, 3h and 3i.

  • Pore structure parameters calculated from the N2 adsorption and desorption isotherms are presented in Table 2. The BET specific surface area ranges from 4.15 to 18.09 m2/g with an average of 11.67 m2/g. The adsorption BJH volume which was calculated at the relative pressure of 0.9 ranges from 0.016 to 0.032 cm3/g with an average of 0.022 cm3/g. The average pore diameter varies from 4.72 to 10.83 nm with an average of 6.41 nm, which indicates mesopores are the dominating pore type. In addition, the maximum of adsorbed quantity is between 10.266 to 21.987 cm3/g with an average of 15.740 cm3/g.

    Samples Average pore
    diameter (nm)
    SBET
    (m2/g)
    VBJH
    (cm3/g)
    Quantity adsorbed
    (cm3/g)
    G-01 10.83 4.15 0.016 10.266
    G-02 6.72 10.84 0.020 16.943
    G-03 4.72 18.09 0.025 18.056
    G-04 6.20 16.30 0.032 21.987
    G-05 5.51 11.91 0.021 14.809
    G-06 6.83 8.22 0.018 12.728
    G-07 5.74 16.53 0.031 21.016
    G-08 5.57 10.87 0.019 13.518
    G-09 5.61 8.15 0.018 12.335

    Table 2.  Pore structure parameters of the Niutitang Formation shale samples obtained from N2 adsorption-desorption isotherms

    The pore size distribution can be described according to the distribution of pore volume for pore size distribution, including differential, incremental and cumulative pore volume distribution curves (Liu et al., 2015; Clarkson, 2013) where we gain the information about pore size range, dominating pore size and pore size distribution peaks. In the case of the tensile strength effect (Gregg and Sing, 1982), the adsorption branch data is more suitable to gain the pore size distribution (Bertier et al., 2016). Based on BJH model, the plots of dV/dlogW versus D (V is the pore volume, and W is the pore diameter) illustrate the pore size distribution of the Niutitang Formation shale (Fig. 5). It can be seen that the distribution of shale samples presents bimodal or multimodal (except for sample G-03) with the major peak between 1.9 and 2.5, 3 and 4, 90 and 110 nm. As a whole, it's observed that the pore size distribution has a wide range between 1.9 and 160 nm.

    Figure 5.  Pore size distribution obtained from the adsorption branch of the N2 adsorption-desorption isotherms of the Niutitang Formation shales.

  • Owing to the intricate shale pore structure, fractal dimension is an effective proxy to reflect the complexity of pore surface roughness and spatial structure (Shao et al., 2017; Hu et al., 2016; Li et al., 2016; Liu et al., 2015). There are several methods to calculate fractal dimensions of porous material, among which Frenkel-Halsey-Hill (FHH) model proves to be the most effective and is widely used because it's only based on nitrogen adsorption data (Yao et al., 2008).

    FHH model can be described as follows.

    where P is the equilibrium pressure; P0, the saturation pressure of nitrogen; V, the adsorption volume at P. C is a constant. If the pores possess fractal features, a plot of lnV versus ln(ln(P0/P)) will show a linear relationship, and K is the slope of the straight- line determined by adsorption mechanism.

    D is the fractal dimension. D can be calculated by

    or

    when van der Waals' force dominates (at the early stage of the multilayer), the former equation fits better. When capillary condensation dominates, the latter equation fits better. Based on the N2 adsorption isotherm data, nine plots of lnV versus ln(ln(P0/P)) were obtained, and two linear segments occurred at a relative pressure of 0–0.45 and 0.45–1, showing two different adsorption mechanisms in two regions (Fig. 6). At a relative low pressure stage, the adsorption is mainly affected by monolayer coverage, and multilayer coverage begins to arise. As the adsorption proceeds, multilayer adsorption strengthens and capillary condensation takes control. The fractal dimensions D1 of the lower relative pressure and the fractal dimensions D2 of the higher relative pressure were both calculated by Eq. (2) and Eq. (3). The calculation results are shown in Table 3. Since some data of D1 and D2 calculated by Eq. (2) is less than 2, which is inconsistent with the theory of fractal dimension on pore structure, Eq. (3) seems more suitable. D1 ranges from 2.558 0 to 2.710 2 averaging at 2.651 6. D2 ranges from 2.541 5 to 2.765 2 averaging at 2.674 2. All fractal dimensions are between 2 and 3, demonstrating that the shale pores possess fractal characteristics. According to Pyun and Rhee (2004), surface fractal dimension represents the pore surface irregularity: the greater the value of the surface fractal dimension is, the more irregular and rougher the pore surface is. Pore structure fractal dimension characterizes the complexity of pore distribution and connectivity in space: when the value of the pore structure fractal dimension increases, the pore structure is more complicated (Li et al., 2016). For this paper, both D1 and D2 are adopted to describe the fractal characteristics. D1 is calculated based on the first linear segment and represents the pore surface fractal dimension. D2 stands for pore structure fractal dimension based on the second segment.

    Figure 6.  Plots of lnV versus ln(ln(P0/P)) reconstructed from the adsorption branch of the N2 adsorption-desorption isotherms of the Niutitang Formation shales samples.

    Samples P/ P0=0–0.45 P/P0=0.45–1
    D1 D2
    Slope (K) R2 3K+3 K+3 Slope (K) R2 3K+3 K+3
    G-01 -0.442 0 0.988 5 1.674 0 2.558 0 -0.458 5 0.995 2 1.624 5 2.541 5
    G-02 -0.351 8 0.983 1 1.944 6 2.648 2 -0.389 9 0.992 9 1.830 3 2.610 1
    G-03 -0.321 8 0.993 0 2.034 6 2.678 2 -0.234 8 0.998 4 2.295 6 2.765 2
    G-04 -0.382 4 0.994 3 1.852 8 2.617 6 -0.308 3 0.994 7 2.075 1 2.691 7
    G-05 -0.328 5 0.989 1 2.014 5 2.671 5 -0.281 3 0.998 1 2.156 1 2.718 7
    G-06 -0.339 8 0.986 8 1.980 6 2.660 2 -0.348 0 0.992 3 1.956 0 2.652 0
    G-07 -0.354 0 0.991 9 1.938 0 2.646 0 -0.289 7 0.998 0 2.130 9 2.710 3
    G-08 -0.325 2 0.984 8 2.024 4 2.674 8 -0.291 9 0.998 3 2.124 3 2.708 1
    G-09 -0.289 8 0.977 8 2.130 6 2.710 2 -0.330 0 0.989 7 2.010 0 2.670 0

    Table 3.  Calculation results of fractal dimensions

  • The relations among pore structure parameters (average pore size, BJH pore volume, and BET specific surface area) of Niutitang Formation shale are illustrated in Fig. 7. There is a negative correlation between BET specific surface area and average pore diameter (R2=0.44) while the relation between BJH pore volume and average pore diameter is not clear (Fig. 7a), which is consistent with Wei et al. (2013) and Zeng et al. (2014) and manifests that with the increasing average pore diameter, BET specific surface area gets smaller and the influence on pore surface area is greater. BJH pore volume increases with increasing BET surface area (R2=0.73 in Fig. 7b). The relations were previously found in the study of Barnett, Haynesville, Marcellus, Woodford, and Doig Phosphate shales in North America (Chalmers et al., 2012) and Wufeng Formation shale (Liang et al., 2015).

    Figure 7.  Relations between (a) BET specific surface area, BJH volume and average pore diameter, (b) BJH volume and BET specific surface area.

    In order to illustrate the influence of shale mineral compositions on pore structure, the relations between pore structure parameters and mineral contents are given in Fig. 8. According to XRD results, Niutitang Formation shale is mainly composed of quartz and clay minerals. Both of quartz and clay minerals content have unclear relations with BET pore specific surface area and BJH pore volume (Figs. 8b–8c, 8e–8f). While there is a positive relation between average pore diameter and quartz content (Fig. 8a, R2=0.63) but a slightly negative correlation between average pore diameter and clay mineral content (Fig. 8d, R2=0.44). However, the relationships between TOC content and average pore diameter, BET surface area and BJH pore volume are ambiguous (Fig. 9). Since the TOC content of our samples is much lower than that of the same formation in another area (Wang et al., 2016; Yang F et al., 2016), it's deduced that organic pores that have greater pore diameter, pore surface area, and pore volume are more developed with higher TOC. Hence, TOC content isn't the dominating factor on pore structure for our samples.

    Figure 8.  Relationships between quartz content and (a) average pore diameter, (b) BET specific surface area, (c) BJH pore volume, and between clay minerals content and (d) average pore diameter, (e) BET specific surface area, (f) BJH pore volume.

    Figure 9.  Relationships between TOC content and (a) average pore diameter, (b) BET specific surface area, (c) BJH pore volume.

  • The relationships between fractal dimensions and pore structure parameters are presented in Fig. 10. Both of D1 and D2 have negative relations with average pore diameter (R2=0.70 and R2=0.81 in Fig. 10a), indicating that fractal dimensions increase with decreasing pore diameter (Shao et al., 2017). D2 has a positive relationship with BET surface area (R2=0.60) while D1 has no apparent relationship with BET surface area (Fig. 10b). There are unclear relationships between D1, D2, and BJH pore volume (Fig. 10c). That's to say; fractal dimensions get larger with increasing pore surface area but with decreasing average pore diameter. Overall, both D1 and D2 are controlled by average pore diameter, and D2 is more correlated with BET specific area. Taking the FE-SEM observation and the low-temperature N2 adsorption-desorption isotherms into consideration, pores of Niutitang Formation shale vary differently in morphology, size and structure complexity. As a result, fractal dimensions can be used to quantify the characteristics of Niutitang Formation shale pores.

    Figure 10.  Relationships between fractal dimensions and pore structure parameters. (a) Plot of D versus average pore diameter; (b) plot of D versus SBET; (c) plot of D versus VBJH.

  • The relationships between fractal dimensions and mineral content are given in Fig. 11. Both of D1 and D2 decrease when quartz content increases (R2=0.45 and R2=0.60 in Fig. 11a). As a result of smooth surface, poor development of secondary pores and primary pores inside quartz particle, just some interparticle pores between quartz (Fig. 3g) which are easily filled with clay or OM, the increasing of quartz content lowers the heterogeneity of pore surface, pore development degree and the complexity of pore structure to some extent, so D1 and D2 come to be smaller. D2 increases when illite content increases (R2=0.45 in Fig. 11b). As for the relationship between clay minerals and fractal dimensions, the laminated structure of clay minerals is easily changed because of activities in post diagenetic stage and various pores and fractures are produced (Figs. 3e, 3h) to increase pore surface area and pore volume and form pore-fracture network, thus D2 slightly increase with increasing illite content. There is no apparent relationship between fractal dimensions D1 and D2 and TOC content (Fig. 11c), and similar discussions can be seen in the study of Loucks et al. (2012) and Liu et al. (2015). It's caused by the poor development of organic pores due to low TOC value and over maturity. This phenomenon testifies that organic pores have little impact on our studied shale pore structure and TOC is not the dominating factor influencing the fractal dimensions.

    Figure 11.  Relationships between fractal dimensions and (a) quartz content, (b) illite content, (c) TOC content.

  • In this paper, the pore structure and pore fractal characteristics of nine samples from the Lower Cambrian Niutitang Formation in the Middle Yangtze area were investigated combining with gas adsorption, FE-SEM observation, and fractal theory. Specific conclusions are as follows.

    (1) The pore types are main plate-like pores and slit- shaped pores, and in FE-SEM, interparticle pores are most developed, followed by intraparticle pores and micro-fracture.

    (2) The BET specific surface area ranges from 4.15 to 18.09 m2/g, the BJH pore volume ranges from 0.016 to 0.032 cm3/g and average pore diameter ranges from 4.72 to 10.83 nm. Pore size distribution shows three main peaks at 1.9–2.5, 3–4 and 90–110 nm and pore size range from 1.9 to 160 nm.

    (3) Shale pores possess different fractal features in the different relative pressure range of 0–0.45 and 0.45–1. Based on FHH model, the pore surface fractal dimension D1 ranges from 2.558 0 to 2.710 2 averaging at 2.651 6, and the pore structure fractal dimension D2 ranges from 2.541 5 to 2.765 2 averaging at 2.674 2. Average pore diameter and quartz content play a vital role in D1 and D2.

  • We sincerely appreciate the editor and reviewers for their valuable comments and suggestions. This study was supported by the National Natural Science Foundation of China (Nos. 41690131, 41572327, 41273001) and the Program of Introducing Talents of Discipline to Universities (No. B14031). The final publication is available at Springer via https://doi.org/10.1007/s12583-020-1259-0.

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