The paper contains main aspects of methodological approach to objective analytic assessment of maximum permissible output of the mine faces from the viewpoint of gas factor. Analytic forecast is centered around the assessment of methane inflow into the face area from all possible sources, based on fundamental physical laws, modern tools of mathematical modeling and in-situ tests of main properties and state parameters of the gas-bearing coal formation. Objective and reliable estimation of permissible outputs is a starting point for justified selection of a seam degassing technology, that has to be based on time factor and predicted value of gas recovery from a coal seam to a degassing well. Recommendations have been formulated on the selection of degassing technology for the coal seam «Boldyrevsky» of the Kirov mine, based on the use of cutting-edge technological schemes (hydraulic fracture, carried out from development workings, etc.), successfully implemented on the mentioned site.
Works in this scientific direction were started in the main coal basins of the USSR about 40 years ago. The basic technology was the technology of hydrodissection of coal seams with subsequent extraction of water and gas. At the depth of occurrence of coal seams more than 500-600 m, the efficiency of this technology begins to decrease and there is a need to develop and use additional physical, physical-chemical, thermodynamic and other active effects on low-permeable, not unloaded from the mining pressure coal seams. The developed methods have no analogues in the world practice and are protected by patents.
The technology of coal bed degassing using the effect of hydraulic impact and redistribution of rock pressure in the bottom-hole zone has been developed and tested in the mines. The basic technology provides hydraulic treatment of coal seam with water injection at pressure of 100-150 atm. Under the proposed technology, at the stage of flowing water from the well in the calculated mode, hydraulic shocks are realized by cyclic overlapping of the water flow, which causes pressure pulses with an amplitude of 170-200 atm. In addition, the technological variant of changing the rock pressure in the vicinity of the borehole by forming slots located along the helical line has been developed. Tangential stresses arise in the coal massif, which leads to increase of its permeability. The given technological variants provide increase of coalbed methane flow rate by 1.5-2 times.
More than 40 years ago, the main basins of the USSR began to carry out advance degassing of coal seams, extracting coalbed methane from the surface through wells. The basic technology is hydrodegasification of coal seams with subsequent extraction of water and gas. For high-gas-bearing coal seams occurring at depths of more than 500-600 m, the technology was improved by developing new ways of active impacts on the coal seam: physical, chemical, thermodynamic and a number of others. New technologies were developed: pneumatic separation, pneumothermal impact, hydrodistraction using gaseous nitrogen, cyclic hydrodistraction using liquefied nitrogen, etc., protected by patents and having no analogues in the world.
The substantiated technologies and installations designed for the extraction of methane from coal seams, as well as the analysis of experience in the operation of mines of the main coal basins of Russia and the countries of the near abroad allow us to draw conclusions about the high efficiency of designs that ensure the safety of mining operations and reduce the unit costs of subsoil reclamation. Promising methods of increasing permeability of coal-bearing formations and stand coals are also investigated.
