Author 1:
Name & Surname: Karkashadze G. G.
Company: National University of Science and Technology — MIS&S (Moscow, Russia)
Work Position: Professor
Scientific Degree: Doctor of Engineering Sciences
Contacts: g-karkashadze@mail.ru

Author 2:
Name & Surname: Mazanik E. V.
Company: SUEK-Kuzbass JSC (Leninsk-Kuznetsky, Russia)
Work Position: Deputy General Director—Director for Aerological Safety
Scientific Degree: Candidate of Engineering Sciences

Author 3:
Name & Surname: Ermak G. P.
Company: Federal Environmental, Industrial and Nuclear Supervision Service of Russia—Rostekhnadzor (Moscow, Russia)
Work Position: Head of Coal Mining Industry Administration
Scientific Degree: Candidate of Engineering Sciences

Participation of S. V. Slastunov, Dr Eng, Prof, MIS&S, in preparation of this article is appreciated.

In predicting the risk of outbursts of coal and gas in underground coal mines, it should be taken into account that the greatest potential source is the energy of absorbed methane, which under hazardous conditions instantly turns into gaseous state and destroys coal. In all cases, the starting mechanism of a coal and methane outburst is the change in the rock pressure and reduction in strength of coal, which initiates growth of micro cracks and subsequent rapid desorption of methane, like a physical explosion. This liberates enormous amounts of energy during expansion of gas. Preliminary coal bed degassing naturally reduces potential energy of coal methane absorbed. Concurrently, coal bed is unladed from the natural rock pressure due to coal shrinkage on degasification. The paper presents the results of modeling stress-strain state of a coal bed under preliminary gas drainage. The boundary conditions of the simulation object take into account vertical and horizontal compressive stresses of rock pressure under the action of gravity. The pressure of methane increases with depth according to the linear law. Differential equations of mass transfer of methane in terms of partial derivatives consider the Langmuir isotherm. The initial condition is was distribution of methane reservoir pressure. According to the results of computer simulation analysis, geomechanical stresses in coal bed depend on the permeability of coal and surrounding rocks. The problem of coal methane drainage in holes is considered. It is shown that shrinkage of coal induces tensile and compressive strains reaching ultimate strength values. This effect can be used for the purpose of targeted geomechanical unloading of gas-bearing coal bed to reduce the extreme rock pressure. As estimates show, the change in the current reservoir pressure of methane only by one bar causes deformation equivalent to the action of multiple normal mechanical stresses. The magnitude of stress when pressure drops by more than five bars may be sufficient to rupture structural elements of coal and to initiate intensive fracturing. The fact of reducing strain energy of rock pressure in degassing process is of great importance for practice as it is established that degassing of reservoir with removal of coal bed methane in the range of 1–2 m³/t provides a significant reduction in energy of rock pressure, which is responsible for starting dangerous geological phenomena. In this case, the factor of rock pressure reduction due to degassing is particularly significant in strata where rock bursts occur.
The study was supported by the Ministry of Education and Science of the Russian Federation, in the framework of the State Task Assignment to the National University of Science and Technology MIS&S (NUST MIS&S), Agreement No. 14.575.210025. Unique identification number RFMEFI57514X0025.

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