Minieiev S.P., Prusova А.А., Yanzhula О.S., Minieiev О.S. Regularity of change in the volmer diffusion coefficient of methane adsorbed in the microsorption structure of the elastic zone of the coal seam bearing pressure

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Parent Category: Geo-Technical Mechanics, 2023
Category: Geo-Technical Mechanics, 2023, Issue 164

Geoteh. meh. 2023, 164, 61-70

https://doi.org/10.15407/geotm2023.164.061

 

REGULARITY OF CHANGE IN THE VOLMER DIFFUSION COEFFICIENT OF METHANE ADSORBED IN THE MICROSORPTION STRUCTURE OF THE ELASTIC ZONE OF THE COAL SEAM BEARING PRESSURE

1Minieiev S.P., 1Prusova А.А., 2Yanzhula О.S., 3Minieiev О.S.

1M.S. Poliakov Institute of Geotechnical Mechanics of the National Academy of Sciences of Ukraine, 2Limited Liability Company «METINVEST KHOLDING», 3Dnipro University of Technology

UDC 622.831.322

Language: English

Abstract. The Volmer diffusion coefficient of methane adsorbed in the micropores of coal in the elastic zone of the coal seam bearing pressure, which normally is under conditions of significant compressive stress, was calculated with taking into account the energy of the methane sorption connection with coal, the energy of Volmer diffusion activation in the porous space of coal, and the stressed state of the elastic zone with its influence on the change of Volmer porosity. During the calculations, such parameters as the diameter of Volmer micropores and the length of the descending branch of the bearing pressure diagram were varied. As a result of the approximation of these calculations, both pairwise dependences of the Volmer diffusion coefficient on the listed parameters and its multifactorial relationship with them were established. Therefore, it is concluded that the process of methane diffusion in the elastic zone of bearing pressure is not blocked by the rock pressure, as previously thought, but is actively developing. The diffusion of free methane will be determined by the established regularity of changes in the Volmer diffusion coefficient in the elastic zone of the coal seam bearing pressure. The calculations show that as the distance from the maximum of the bearing pressure increases, the Volmer diffusion coefficient of methane in the coal seam increases, which is due to a decrease in the pressure of rocks in the descending branch of the bearing pressure diagram. However, this growth is not great due to the weak compressibility of pores. Therefore, for pores of the same diameter, the Volmer diffusion coefficient in the elastic zone of the coal seam bearing pressure for the given mining geological conditions can be considered a constant. For depths of, for example, 1000 m and pore diameters of 10 Å, the value of the Volmer diffusion coefficient will be approximately 3.77·10-8 m2/s. This confirms that methane gas release is caused not only by filtration of free gas, but also by Volmer diffusion of adsorbed methane. In turn, the reserves of the latter are known to be the main reserves of methane in coal. Therefore, the established regularity makes it possible to more accurately calculate the volumes of methane, which will be released from the coal massif during mining operations, in order to assess safety of conditions for coal deposits mining and to develop technologies for coal mine methane production.
Keywords: adsorbed methane, microstructure of a coal seam, Volmer pores, area of bearing pressure, elastic zone, Volmer diffusion coefficient.

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About authors:

Minieiev Serhii Pavlovych, Doctor of Technical Sciences (D.Sc.), Professor, Head of the Department of Pressure Dynamics Control in Rocks, M.S. Poliakov Institute of Geotechnical Mechanics of the National Academy of Sciences of Ukraine (IGTM of the NAS of Ukraine), Dnipro, Ukraine, This email address is being protected from spambots. You need JavaScript enabled to view it.

Prusova Alla Andriivna, Candidate of Technical Sciences (Ph.D.), Senior Researcher, M.S. Poliakov Institute of Geotechnical Mechanics of the National Academy of Sciences of Ukraine (IGTM of the NAS of Ukraine), Dnipro, Ukraine.

Yanzhula Oleksii Serhiiovych, Candidate of Technical Sciences (Ph.D.), Director of the Directorate for Technical Development and Investments, Limited Liability Company «METINVEST KHOLDING», Dnipro, Ukraine.

Minieiev Oleksandr Serhiiovych, Candidate of Technical Sciences (Ph.D.), Associate Professor, Dnipro University of Technology (NTU "DP"), Dnipro, Ukraine.