DYNAMICS OF CHANGES IN THE VOLMER DIFFUSION COEFFICIENT OF METHANE ADSORBED IN THE MICROSORPTION STRUCTURE OF THE RESISTANT PRESSURE ELASTIC ZONE OF A COAL LAYER
Authors:   Head of Department М.S. Poliakov Institute of Geotechnical Mechanics under the National Academy of Sciences of Ukraine, Minieiev S. , Prusova A. ,   М.S. Poliakov Institute of Geotechnical Mechanics under the National Academy of Sciences of Ukraine, Yanzhula O. ,   М.S. Poliakov Institute of Geotechnical Mechanics under the National Academy of Sciences of Ukraine, Minieiev O. ,   Dnipro University of Technology
Published: July 2023

Purpose. Set the possible change in the coefficient of Volmer diffusion of methane in the microsorption structure of the elastic zone of the supporting pressure of the coal seam. Methodology. The energy of the sorption bond of methane with the coals, the activation energy of the Volmer diffusion in the porous expanse of coal, as well as the stresses of the elastic zone and its effect on the change of the Volmer porosity, was taken into account. In the calculations, such parameters as the diameter of the Volmer micropores and the length of the descending branch of the support pressure diagram were varied. Results. Approximation of calculations made it possible to establish both the pairwise dependences of the Volmer diffusion coefficient on the listed parameters and its multifactorial relationship with them. It was concluded that the diffuse process of methane in the elastic support pressure zone is not blocked by rock pressure, as previously thought, but is actively developing. In this case, the diffusion of free methane will be determined by the established pattern of change in the Volmer diffusion coefficient in the elastic zone of the coal seam bearing pressure. Calculations showed that as the distance from the maximum reference pressure increases, the Volmer diffusion coefficient of methane in the coal seam increases, which is due to a decrease in rock pressure in the descending branch of the reference pressure graph. However, this growth is not strong due to the weak compressibility of pores. Therefore, for pores of the same diameter, the Volmer diffusion coefficient in the elastic zone of the supporting pressure of the coal seam 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. Scientific novelty. Calculations of the Volmer diffusion coefficient of methane adsorbed in the micropores of coal in the elastic zone of the supporting pressure of the coal seam, which, of course, is under significant compressive stresses, have been performed. The established phenomenon confirms that methane gas release is determined not only by free gas filtration, but also by Volmer diffusion of adsorbed methane. Practical significance. Since adsorbed methane reserves are known to be the main methane reserves in coal, the regularity established in the article makes it possible to more accurately calculate the volumes of methane that will be released from the coal massif during mining operations for the assessment of safe working conditions for coal deposits and for the development of technologies for the production of shale methane.