Vasilkovsky V.A., Mineev S.P. Some regularities of methane drifting in fractals of coal matter
- Details
- Parent Category: Geo-Technical Mechanics, 2018
- Category: Geo-Technical Mechanics, 2018, Issue 138
Geoteh. meh. 2018, 138, 93-107
DOI: https://doi.org/10.15407/geotm2018.01.093
Some regularities of methane drifting in fractals of coal matter
Vasilkovsky V.A., Mineev S.P.
Авторы:
Vasilkovsky V.A., Dr. Tech. Sci., Leading Researcher (IFGP NAS of Ukraine)
Mineev S.P., Dr. Tech. Sciences, Professor, Head of Department (IGTM NAS of Ukraine)
UDC 533.6.011: 533.583.2
Language:Russian
Abstract.
Scenario of methane drifting and methods for stimulating its escape from coal depends not only on mechanical properties of coal in the stratum but also on parameters of gas subsystem, phase state of methane and its distribution in the coal matter. Therefore, determination of phase states of methane, its volume and pattern of its distribution in the coal matter is still a live problem.
Purpose of the research was to obtain information on methane distribution and mechanisms of methane drifting in coal blocks. Experimental base of the research was obtained by the authors data on kinetics of methane desorption from 9 coal samples with different levels of metamorphism. Experimental procedure included saturation of coal, crushed to fraction of 0.2‑0.25 mm, by methane at temperature of 300 K in a high-pressure chamber (4.5 MPa) for 10 days. Subsequent desorption was measured in a vessel of known volume. Kinetics of the vessel filling was observed visually and registered in real time with interval of 0.65 s.
For interpreting the experimental data, a new analysis method based on typical time of desorption was applied. Information on the value of effective diffusion coefficient, Deff, and on character of its change during desorption was obtained. It is found that value of the Deff is changed during desorption within 10‑9‑10‑11 m2/s (for anthracite) and up to 10‑11‑10‑14 m2/s (for candle coal). Change of parameter Deff by 2‑3 orders with gas emission indicates a complex structure of coal blocks. Further analysis was carried out within the block model of the coal structure, in which blocks were weakly ordered elements of the coal substance with low permeability. Presence of methane in the block leads to formations in the form of coal-methane solution.
It is shown that, in contrast with other types of diffusion, coefficient of Volmer diffusion decreases with increase of temperature and, hence, depth of mining and changes as much as almost half with decrease of diameter of the coal spore (from 12A to 9A). It was found that decrease of volatile substance content in coal is accompanied by increased ordering of structure of its blocks and their permeability. Nature of methane distribution in the blocks was analyzed with assumption that the upper limit for the coefficient of solid-state diffusion does not exceed 10‑12 m2/s. Data on percentage content of methane in solution and in mesopores in adsorbed state were obtained. Comparison of kinetics of methane and inertia gas drifting shows that, in contrast with other matters, which do not adsorb gases enough, molecules move in the form of surface diffusion in transition pores and micropores.
Keywords:
methane, coal, coal blocks, metamorphism, effective diffusion coefficient, solid-state and Volmer diffusion, diffusion along the surface of the pores.
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About the authors
Vasilkovsky Vsevolod Alekseevich, Doctor of Technical Sciences (D. Sc.), Head of the department in Institute for Physics of Mining Processes National Academy Sience of Ukraine (IPMP NAS of Ukraine), Dnipro, Ukraine, This email address is being protected from spambots. You need JavaScript enabled to view it.
Mineev Sergey Pavlovich, Doctor of Technical Sciences (D. Sc.), Professor, Head of the department, Institute of Geotechnical Mechanics named by N. Polyakov of National Academy of Science of Ukraine (IGTM NASU), Dnipro, Ukraine, This email address is being protected from spambots. You need JavaScript enabled to view it.
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