Abstract
Coal pores not only serve as the storage space for coalbed methane but also provide channels for gas migration. The accurate characterization of coal pore structures is of significance to study the methane adsorption behaviors. In this work, the quantitative relationship between gas adsorption and pore characteristics was investigated in depth for bituminous coals. Results of scanning electron microscopy showed that the surface morphological characteristics of these samples differ greatly. Some typical pore types including cylindrical pores and conical pores were found in these samples. The remarkable hysteresis loop was observed, which is attributed to the bottle-shaped pores with poor connectivity. Fractal theory was introduced to quantitatively evaluate the surface roughness of coal. Pore fractal dimensions, D1 and D2, were calculated using low-pressure N2 gas adsorption data, and their values were in the range of 2.125–2.721 and 2.084–2.461, respectively. D1 was larger than the corresponding D2 for the same sample, suggesting that micropore structures in coal were more complex when compared with mesopores and transition pores. Both D1 and D2 were enhanced with increase in micropore specific surface area, but they were reduced with increase in mesopore specific surface area. Gas adsorption in coal was estimated from the perspective of fractal dimension. Judging from the fitting degree, the influence of D1 on adsorption capacity of coal was remarkably greater than that of D2. D1 is expected to be used as one of the major adsorption indicators in the future study.
Similar content being viewed by others
References
Cavelan, A., Boussafir, M., Mathieu, N., & Laggoun-Défarge, F. (2020). Impact of thermal maturity on the concomitant evolution of the ultrafine structure and porosity of marine mudstones organic matter; contributions of electronic imaging and new spectroscopic investigations. International Journal of Coal Geology, 231, 103622.
Ceglarska-Stefańska, G., & Brzóska, K. (1998). The effect of coal metamorphism on methane desorption. Fuel, 77, 645–648.
Chalmers, G. R. L., & Bustin, R. M. (2007). On the effects of petrographic composition on coalbed methane sorption. International Journal of Coal Geology, 69(4), 288–304.
Chandra, D., Vishal, V., Bahadur, J., & Sen, D. (2020). A novel approach to identify accessible and inaccessible pores in gas shales using combined low-pressure sorption and SAXS/SANS analysis. International Journal of Coal Geology, 228, 103556.
Chattaraj, S., Mohanty, D., Kumar, T., Halder, G., & Mishra, K. (2019). Comparative study on sorption characteristics of coal seams from Barakar and Raniganj formations of Damodar Valley Basin, India. International Journal of Coal Geology, 212, 103202.
Chen, K., Liu, X. F., Wang, L. K., Song, D. Z., Nie, B. S., & Yang, T. (2021). Influence of sequestered supercritical CO2 treatment on the pore size distribution of coal across the rank range. Fuel, 306, 121708.
Chen, L. W., Wang, L., Yang, T. H., & Yang, H. M. (2021). Deformation and swelling of coal induced from competitive adsorption of CH4/CO2/N2. Fuel, 286, 119356.
Chen, M., Yang, Y., Gao, C., Cheng, Y. P., Wang, J. C., & Wang, N. (2020). Investigation of the fractal characteristics of adsorption-pores and their impact on the methane adsorption capacity of various rank coals via N2 and H2O adsorption methods. Energy Science & Engineering, 8(9), 3228–3243.
Clarkson, C. R., & Bustin, R. M. (1999). The effect of pore structure and gas pressure upon the transport properties of coal: A laboratory and modeling study. 2. Adsorption rate modeling. Fuel, 78(11), 1345–1362.
Crosdale, P. J., Beamish, B. B., & Valix, M. (1998). Coalbed methane sorption related to coal composition. International Journal of Coal Geology, 35(1–4), 147–158.
De Boer, J. H. (1958). The shape of capillaries (pp. 68–92). Butterworth.
Farmer, I. W., & Pooley, F. D. (1967). A hypothesis to explain the occurrence of outbursts in coal, based on a study of West Wales outburst coal. International Journal of Rock Mechanics and Mining Sciences, 4(2), 189–193.
Fernandez-Diaz, J. J., Gonzalez-Nicieza, C., Alvarez-Fernandez, M. I., & Lopez-Gayarre, F. (2013). Analysis of gas-dynamic phenomenon in underground coal mines in the central basin of Asturias (Spain). Engineering Failure Analysis, 34, 464–477.
Gao, W., Yi, T. S., & Jin, J. (2017). Pore integrated fractal characteristics of coal sample in western Guizhou and its impact to porosity and permeability. Journal of China Coal Society, 42(5), 1258–1265.
Garbacz, J. K. (1998). Fractal description of partially mobile single gas adsorption on energetically homogeneous solid adsorbent. Colloid Surfaces A, 143(1), 95–101.
Gentzis, T. (2000). Subsurface sequestration of carbon dioxide-an overview from an Alberta (Canada) perspective. International Journal of Coal Geology, 43, 287–305.
Gerami, A., Armstrong, R. T., Jing, Y., Wahid, F. A., Arandiyan, H., & Mostaghimi, P. (2019). Microscale insights into gas recovery from bright and dull bands in coal. Journal of Petroleum Science and Engineering, 172, 373–382.
Groshong, R. H., Jr., Pashin, J. C., & McIntyre, M. R. (2009). Structural controls on fractured coal reservoirs in the southern Appalachian Black Warrior foreland basin. Journal of Structural Geology, 31(9), 874–886.
Hamawand, I., Yusaf, T., & Hamawand, S. G. (2013). Coal seam gas and associated water: A review paper. Renewable and Sustainable Energy Reviews, 22, 550–560.
He, X., Liu, X., Nie, B., & Song, D. (2017). FTIR and Raman spectroscopy characterization of functional groups in various rank coals. Fuel, 206, 555–563.
He, X., Liu, X., Song, D., & Nie, B. (2019). Effect of microstructure on electrical property of coal surface. Applied Surface Science, 483, 713–720.
Jing, Y., Armstrong, R. T., Ramandi, H. L., & Mostaghimi, P. (2017). Topological characterization of fractured coal. Journal of Geophysical Research: Solid Earth, 122(12), 9849–9861.
Karacan, C. O., & Okandan, E. (2001). Adsorption and gas transport in coal microstructure: Investigation and evaluation by quantitative X-ray CT imaging. Fuel, 80, 509–520.
Karacan, C. Ö., Ruiz, F. A., Cotè, M., & Phipps, S. (2011). Coal mine methane: A review of capture and utilization practices with benefits to mining safety and to greenhouse gas reduction. International Journal of Coal Geology, 86(2–3), 121–156.
Keshavarz, A., Sakurovs, R., Grigore, M., & Sayyafzadeh, M. (2017). Effect of maceral composition and coal rank on gas diffusion in Australian coals. International Journal of Coal Geology, 173, 65–75.
Kiani, A., Sakurovs, R., Grigore, M., & Sokolova, A. (2018). Gas sorption capacity, gas sorption rates and nanoporosity in coals. International Journal of Coal Geology, 200, 77–86.
Kong, X. G., Li, S. G., Wang, E. Y., Ji, P. F., Wang, X., Shuang, H. Q., & Zhou, Y. X. (2021). Dynamics behaviour of gas-bearing coal subjected to SHPB tests. Composite Structures, 256, 113088.
Kong, X. G., Li, S. G., Wang, E. Y., Wang, X., Zhou, Y. X., Ji, P. F., Shuang, H. Q., Li, S. R., & Wei, Z. Y. (2021). Experimental and numerical investigations on dynamic mechanical responses and failure process of gas-bearing coal under impact load. Soil Dynamics and Earthquake Engineering, 142, 106–579.
Li, Q., Liu, D. M., Cai, Y. D., Zhao, B., Lu, Y. J., & Zhou, Y. F. (2021). Effects of natural micro-fracture morphology, temperature and pressure on fluid flow in coals through fractal theory combined with lattice Boltzmann method. Fuel, 286, 119–468.
Li, W., Liu, H., & Song, X. (2015). Multifractal analysis of Hg pore size distributions of tectonically deformed coals. International Journal of Coal Geology, 144, 138–152.
Liao, Z. W., Liu, X. F., Song, D. Z., He, X. Q., Nie, B. S., Yang, T., & Wang, L. K. (2021). Micro-structural damage to coal induced by liquid CO2 phase change fracturing. Natural Resources Research, 30(2), 1613–1627.
Liu, S. M., Li, X. L., Wang, D. K., & Zhang, D. M. (2021b). Experimental study on temperature response of different ranks of coal to liquid nitrogen soaking. Natural Resources Research, 30(2), 1467–1480.
Liu, X., Nie, B., Wang, W., Wang, Z., & Zhang, L. (2019b). The use of AFM in quantitative analysis of pore characteristics in coal and coal-bearing shale. Marine and Petroleum Geology, 105, 331–337.
Liu, X., Song, D., He, X., Wang, Z., Zeng, M., & Deng, K. (2019d). Nanopore structure of deep-burial coals explored by AFM. Fuel, 246, 9–17.
Liu, X. F., & Nie, B. S. (2016). Fractal characteristics of coal samples utilizing image analysis and gas adsorption. Fuel, 182, 314–322.
Liu, X. F., Nie, B. S., Guo, K. Y., Zhang, C. P., Wang, Z., & Wang, L. K. (2021). Permeability enhancement and porosity change of coal by liquid carbon dioxide phase change fracturing. Engineering Geology, 287, 106106.
Liu, X. F., Song, D. Z., He, X. Q., Nie, B. S., & Wang, L. K. (2019a). Insight into the macromolecular structural differences between hard coal and deformed soft coal. Fuel, 245, 188–197.
Liu, X. F., Song, D. Z., He, X. Q., Wang, Z. P., Zeng, M. R., & Wang, L. K. (2019c). Quantitative analysis of coal nanopore characteristics using atomic force microscopy. Powder Technology, 346, 332–340.
Liu, X. F., Wang, Z. P., Song, D. Z., He, X. Q., & Yang, T. (2020). Variations in surface fractal characteristics of coal subjected to liquid CO2 phase change fracturing. International Journal of Energy Research, 44(11), 8740–8753.
Loucks, R. G., Reed, R. M., Ruppel, S. C., & Jarvie, D. M. (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.
Lu, G., Wang, J., & Wei, C. (2018). Pore fractal model applicability and fractal characteristics of seepage and adsorption pores in middle rank tectonic deformed coals from the Huaibei coal field. Journal of Petroleum Science and Engineering, 171, 808–817.
Lu, G., Wei, C., Wang, J., Meng, R., & Tamehe, L. S. (2021). Influence of pore structure and surface free energy on the contents of adsorbed and free methane in tectonically deformed coal. Fuel, 285, 119087.
Mahamud, M., López, Ó., Pis, J. J., & Pajares, J. A. (2003). Textural characterization of coals using fractal analysis. Fuel Processing Technology, 81(2), 127–142.
Mendhe, V. A., Bannerjee, M., Varma, A. K., Kamble, A. D., Mishra, S., & Singh, B. D. (2017). Fractal and pore dispositions of coal seams with significance to coalbed methane plays of East Bokaro, Jharkhand, India. Journal of Natural Gas Science and Engineering, 38, 412–433.
Moore, T. A. (2012). Coalbed methane: A review. International Journal of Coal Geology, 101(1), 36–81.
Mostaghimi, P., Armstrong, R. T., Gerami, A., Hu, Y., Jing, Y., Kamali, F., Liu, M., Liu, Z. S., Lu, X., Ramandi, H. L., Zamani, A., & Zhang, Y. L. (2017). Cleat-scale characterisation of coal: An overview. Journal of Natural Gas Science and Engineering, 39, 143–160.
Murata, S., Hosokawa, M., Kidena, K., & Nomura, M. (2000). Analysis of oxygen-functional groups in brown coals. Fuel Processing Technology, 67(3), 231–243.
Nie, B. S., Liu, X. F., Yang, L. L., Meng, J. Q., & Li, X. C. (2015). Pore structure characterization of different rank coals using gas adsorption and scanning electron microscopy. Fuel, 158, 908–917.
Nie, B. S., Liu, X. F., Yuan, S. F., Ge, B. Q., Jia, W. J., & Chen, X. H. (2016). Sorption charateristics of methane among various rank coals: Impact of moisture. Adsorption, 22(3), 315–325.
Nie, B. S., Ma, Y. K., Hu, S. T., & Meng, J. Q. (2019). Laboratory study phenomenon of coal and gas outburst based on a mid-scale simulation system. Scientific Reports, 9, 15005.
Niu, Q., Cao, L., Sang, S., Wang, W., Zhou, X., Yuan, W., Ji, Z., Chang, J., & Li, M. (2021). Experimental study on the softening effect and mechanism of anthracite with CO2 injection. International Journal of Rock Mechanics and Mining Sciences, 138, 104614.
Niu, Q., Cao, L., Sang, S., Zhou, X., Wang, W., Yuan, W., Ji, Z., Wang, H., & Nie, Y. (2020). Study on the anisotropic permeability in different rank coals under influences of supercritical CO2 adsorption and effective stress and its enlightenment for CO2 enhance coalbed methane recovery. Fuel, 262, 116515.
Pan, J., Niu, Q., & Wang, K. (2016). The closed pores of tectonically deformed coal studied by small-angle X-ray scattering and liquid nitrogen adsorption. Microporous and Mesoporous Materials, 224, 245–252.
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), 3558–65.
Ruppel, T. C., Grein, C. T., & Bienstock, D. (1974). Adsorption of methane on dry coal at elevated pressure. Fuel, 53(3), 152–162.
Sampath, K. H. S. M., Perera, M. S. A., Matthai, S. K., Ranjith, P. G., & Li, D. Y. (2020). Modelling of fully-coupled CO2 diffusion and adsorption-induced coal matrix swelling. Fuel, 262, 116486.
Siddiqui, M. A. Q., Ueda, K., Komatsu, H., Shimamoto, T., & Roshan, H. (2020). Caveats of using fractal analysis for clay rich pore systems. Journal of Petroleum Science and Engineering, 195, 107622.
Song, D. Z., Liu, X. F., He, X. Q., Nie, B. S., & Wang, W. X. (2021). Investigation on the surface electrical characteristics of coal and influencing factors. Fuel, 287, 119–551.
Wang, Z. Y., Cheng, Y. P., Wang, L., Zhou, H. X., He, X. X., Yi, M. H., & Xi, C. P. (2020). Characterization of pore structure and the gas diffusion properties of tectonic and intact coal: Implications for lost gas calculation. Process Safety and Environmental Protection, 135, 12–21.
Wojtacha-Rychter, K., Honanie, N., & Smoliński, A. (2020). Effect of porous structure of coal on propylene adsorption from gas mixtures. Scientific Reports, 10(1), 1–11.
Xia, B. W., Liu, X. F., Song, D. Z., He, X. Q., Yang, T., & Wang, L. K. (2021). Evaluation of liquid CO2 phase change fracturing effect on coal using fractal theory. Fuel, 287, 119569.
Xie, H. P. (1996). Fractals—An introduction to rock mechanics (pp. 15–23). Science Press.
Zhang, D. F., Li, C., Zhang, J., Lun, Z. M., Jia, S. Q., Luo, C. J., & Jiang, W. P. (2019a). Influences of dynamic entrainer-blended supercritical CO2 fluid exposure on high-pressure methane adsorption on coals. Journal of Natural Gas Science and Engineering, 66, 180–191.
Zhang, D. F., Liu, S. L., Fu, X. X., Jia, S. Q., Min, C. G., & Pan, Z. J. (2019b). Adsorption and desorption behaviors of nitrous oxide on various rank coals: Implications for oxy-coal combustion flue gas sequestration in deep coal seams. Energy & Fuels, 33(11), 11494–11506.
Zhang, M., Chakraborty, N., Karpyn, Z. T., Emami-Meybodi, H., & Ayala, L. F. (2021). Experimental and numerical study of gas diffusion and sorption kinetics in ultratight rocks. Fuel, 286, 119300.
Acknowledgments
This study was financially supported by the National Natural Science Foundation of China (Grant Nos. 52004042, U19B2009), Open Fund of Shaanxi Key Laboratory of Geological Support for Coal Green Exploitation (No. DZBZ2020-10), the State Key Laboratory Cultivation Base for Gas Geology and Gas Control (Henan Polytechnic University) (Grant No. WS2019B08).
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Liu, X., Kong, X., Nie, B. et al. Pore Fractal Dimensions of Bituminous Coal Reservoirs in North China and Their Impact on Gas Adsorption Capacity. Nat Resour Res 30, 4585–4596 (2021). https://doi.org/10.1007/s11053-021-09958-7
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11053-021-09958-7