Sorption isotherm is dependence between the specific mass of methane contained in a unit volume of coal and its pore pressure, and it is constructed based on the Langmuir dependence. Two coefficients included in this dependence are determined from the solution of the system of equations after the values of the specific mass of methane in two different places of the reservoir are determined. In this regard, a control well is drilled from the face of mining working, and measurements of methane parameters are made from it at two different depths. These parameters include the initial rate of gas release from the well and the pressure of methane in it.
The initial outgassing rate is determined using a flow meter. And for pressure measurements, capital sealing of the well is required since the pressure of methane in it can squeeze out the sealer. Therefore, for these purposes, it is proposed to use not a sealer, but a spherical shell into which methane enters from the well. The shell material is adopted with low stiffness characteristics therefore it is easy to measure its dimensions.
Deformation of the shell under the action of excessive pressure of methane is associated with its geometric and physical-mechanical parameters, which are determined by the well-known formulas of the theory of shells. Knowing the magnitude of shell deformation, it is easy to calculate the methane excess pressure.
According to the conclusions of Academician S.A. Khristianovich the filtration processes in a coal seam with a moving free edge are stationary, and isothermal. Therefore, it is not difficult to switch from the excess pressure in the shell to the pressure in the well, and, consequently, to the pore pressure of methane. With known values of the initial gas release rate and methane pressure, it is easy to calculate the specific mass of the methane in the well in two of its sections, and then determine the porosity coefficients from the Langmuir equation.
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