Academician Melnikov Institute of Integrated Mineral Development – IPKON, Russian Academy of Sciences, Moscow, Russia:

V. A. Bobin, Head of Department, Doctor of Engineering Sciences
O. N. Malinnikova, Head of Laboratory, Doctor of Engineering Sciences
V. N. Odintsev, Leading Researcher, Doctor of Engineering Sciences, odin-vn@yandex.ru
V. A. Trofimov, Leading Researcher, Doctor of Engineering Sciences

The concept of the governing role of coal microstructure in the mechanism of fast transition of methane between the bound and unbound states and on participation of methane in gas-dynamic fracture of coal, starting from micro-scale, is developed. The concept contains two determinative factors – transition of methane molecules between bound and unbound state and ability of free methane to disintegrate coal in micro-fractures. The studies used the methods of fractal analysis of multi-scale images of damage obtained in outburst-hazardous and outburst-nonhazardous coal using a scanning electron microscope with the resolving power around 100 nm; analytical estimation of time of bound methane molecule liberation from coal particles by the mechanism of diffusion; assessment of stress state of coal particles after contact interaction between them and the theory of tensile micro-fracturing due to release of methane molecules in the fracture space. It follows from the joint analysis of methane desorption and coal fracture conditions that the governing role of coal micro-structure is conditioned by the possibility to determine participation of bound methane in the dynamic fracture of coal at a micro-level. Moreover, by contrast to unbound methane initially occurring in coal, disintegration of coal by bound methane should unavoidably transfer to larger scales. Peculiarities of bound methane conditions in coal (occluded or dissolved methane) are of no high importance for gasdynamic fracture of coal. The undertaken research supports the conclusion that the analysis of coal damage at a micro-scale can be an efficient method to predict coal and gas outbursts in coal beds.

1. Malyshev Yu. N., Trubetskoy K. N., Ayruni A. T. Fundamentally applied methods of solving the coal layer methane problems. Moscow : Izdatelstvo Akademii gornykh nauk, 2000. 519 p.
2. Bobin V. A. Sorption processes in natural coal and its structure. Moscow : IPKON AN SSSR, 1987. 135 p.
3. Ettinger I. L. Diffusion field in coal layer. Fiziko-tekhnicheskie problemy razrabotki poleznykh iskopaemykh. 1991. No. 4. pp. 109–111.
4. Ulyanova E. V. Structural and composite reconstructions in fossil coals. Connection of microstructure with kinetics of mining processes. Saarbrücken : Palmarium Academic Publishing, 2012. 304 p.
5. Khristianovich S. A., Salganik R. L. Sudden emissions of coal (rock) and gas. Stresses and strains. Preprint Instituta problem mekhaniki AN SSSR. 1980. No. 153. 75 p.
6. Litwiniszyn J. Rarefaction Shock Waves, Outbursts Consequential Coal Damage. International Journal of Rock Mechanics and Mining Science & Geomechanics Abstracts. 1990. 27, Iss. 6. pp. 535–540.
7. Huoyin Li. Major and minor structural features of bedding shear zone along a coal seam and related gas outburst, Pingdingshan coalfield, northern China. International Journal of Coal Geology. 2001. Vol. 47, Iss. 2. pp. 101–113.
8. Fan Chaojun, Li Sheng, Luo Mingkun, Du Wenzhang, Yang Zhenhua. Coal and gas outburst dynamic system. International Journal of Mining Science and Technology. 2017. Vol. 27, Iss. 1. pp. 49–55.
9. An F. H., Cheng Y. P. An explanation of large-scale coal and gas outbursts in underground coal mines: the effect of low-permeability zones on abnormally abundant gas. Natural Hazard Earth System Sciences. 2014. Vol. 14. pp. 2125–2132.
10. Guan P., Wang H., Zhang Y. Mechanism of instantaneous coal outbursts. Geology. 2009. Vol. 37, No. 10. pp. 915–918.
11. Sidorenko A. A., Sishchuk J. M., Gerasimova I. G. Underground mining of multiple coal seams: Problems and solutions. Eurasian Mining. 2016. No. 2. pp. 11–15. DOI: 10.17580/em.2016.02.03
12. Wang S., Elsworth D., Liu J. Rapid decompression and desorption indused energetic failure in coal. Journal of Rock Mechanics and Geotechnical Engineering. 2015. Vol. 7, Iss. 3. pp. 345–350.
13. Feldman E. P., Vasilenko T. A., Kalugina N. A. Physical kinetics of coal-methane system: Mass transfer, pre-outburst events. Fiziko-tekhnicheskie problemy razrabotki poleznykh iskopaemykh. 2014. No. 3. pp. 46–65.
14. Bazhin V. Yu., Feshchenko R. Yu., Ramana G. V., Shabalov M. Yu. Extreme low-grade coal treatment coupled with X-ray testing. CIS Iron and Steel Review. 2016. No. 1. pp. 4–8. DOI: 10.17580/cisisr.2016.01.01
15. Dyrdin V. V., Smirnov V. G., Shepeleva S. A. Parameters of methane condition during phase transition at the outburst-hazardous coal seam edges. Fiziko-tekhnicheskie problemy razrabotki poleznykh iskopaemykh. 2013. No. 6. pp. 78–82.
16. Alekseev A. D., Vasilenko T. A., Gumennik K. V., Kalugina N. A., Fel'dman E. P. Diffusion-filtration model of methane escape from a coal seam. Zhurnal tekhnicheskoy fiziki. 2007. Vol. 77, No. 4. pp. 65–74.
17. Trubetskoy K. N., Ruban A. D., Viktorov S. D., Malinnikova O. N., Odintsev V. N. et al. Fractal structure of deformed coal beds and their susceptibility to gas-dynamic failure. Doklady Akademii nauk. 2010. Vol. 431, No. 6. pp. 818–821.

18. Smith T. G., Lange G. D., Marks W. B. Fractal methods and results in cellular morphology – dimensions, lacunarity and multifractals. Journal of Neuroscience Methods. 1996. Vol. 69, Iss. 2. pp. 123–136.
19. Malinnikova O. N., Malinnikov V. A., Uchaev D. V., Uchaev D. V. About the effect of noises, caused by coal sample images SEM on the assessment of coal inclination to sudden emissions. Deformation and destruction of defected materials and dynamic phenomena in rocks and excavations : thesis of reports of the XXVI International scientific school named by Academician S. A. Khristianovich. Alushta, 2016. pp. 134–139.
20. Savinykh V. P., Malinnikov V. A., Uchaev D. V., Uchaev D. V. Automated technology of decoding and analysis of linear and ring structures on space images. Izvestiya vuzov. Geodeziya i aerofotosemka. 2012. No. 6. pp. 53–65.
21. Malinnikova O. N., Odintsev V. N., Trofi mov V. A. Assessment of conditions of coal methane yield on microstructure level. Gornyy informatsionno-analiticheskiy byulleten. 2009. Special issue No. 11. Methane. pp. 189–204.
22. Kuznetsov S. V., Trofimov V. A. Gasdynamics in a coal seam. Part 1: Mathematical description of the desorption kinetics. Fiziko-tekhnicheskie problemy razrabotki poleznykh iskopaemykh. 2009. No. 1. pp. 6–14.
23. Nazarova L. A., Nazarov L. A. Evolution of stresses and permeability of fractured-and-porous rock mass around a production well. Fiziko-tekhnicheskie problemy razrabotki poleznykh iskopaemykh. 2016. No. 3. pp. 11–19.
24. Nazarova L. A., Nazarov L. A. Inverse Problems in Geomechanics: Diagnostics and Prediction of the State of Rock Masses with Estimating Their Properties. Applied Inverse Problems: Select Contributions from the First Annual Workshop on Inverse Problems : Conference proceedings. New York : Springer, 2013. Vol. 48. pp. 95–103.
25. Atkinson B. K. Fracture Mechanics of Rock. London : Academic Press, 1987. 546 p.
26. Bobin V. A., Zimakov B. M., Odintsev V. N. Assessment of energy of inter-molecular repulsion of sorbate molecules in coal micropores. Fiziko-tekhnicheskie problemy razrabotki poleznykh iskopaemykh. 1989. No. 5. pp. 48–56.
27. Urakaev F. Kh. Theoretical and applied aspects of mechanochemistry of inorganic substances. Modelling of mechanochemical processes. Saarbrücken : LAP Lambert Academic Publishing, 2011. 408 p.