Coal Containing Methane Fluid-solid Coupling Mathematical Model And Its Application

In order to study the migration law of gas in the coal containing methane. Based onthe principle of effective stress in porous media, considering the porosity, the dynamicvariation of the permeability and the elastic-plastic constitutive relationship of coalcontaining gas, establish a elastic-plastic fluid solid coupling mathematical model ofcoal containing gas. Use COMSOL Multiphysics to verify the correctness of the model.At the same time, we analysis the factors affecting of gas boreholes in coal containinggas. This paper has made the following findings:(1) The elastic-plastic fluid solid coupling mathematical model of coal containinggas is established. Compared to the laboratory results and simulation results，The resultsshow that: the model established in this paper can reflect the seepage law of gas anddeformation characteristics of coal.(2) By analysis the factors affecting of gas boreholes in coal containing gas, drawsthe following conclusion:①Coal seam gas pressure will decrease with the increase of time, and at the initialstage of drilling pump gas pressure decreased significantly, with the drainage timeincrease of coal seam gas pressure is reduced fall velocity.②Gas drilling drainage process will make the coal and rock skeleton effectivestress should be increased, resulting in the coal and rock porosity and permeabilitydecreasing, it is for this reason that coal seam gas drainage gas pressure, the rate ofdecline slowed down significantly in late.③Confining pressure will affect the distribution of gas pressure, with the increaseof confining pressure, the gas pressure will increase, and porosity and permeability willdecrease, but near the drainage hole pressure drop obviously. Coal unloading conditionswill conducive to gas drainage.④The effect of negative pressure pumping is very limited to coal seam inner gaspressure change. Negative pressure drainage is just slightly reducing gas pressurearound the borehole. For away from the drilling drainage region, the negative pressurepumping effect on coal seam gas pressure distribution is almost negligible.⑤Increase the borehole radius is helpful to reduce the coal inner gas pressure andexpand the effective drainage radius; at one time, effective drainage radius increaseswith the hole radius, but with the increase of hole radius, this increased trend will continue to slow down.⑥In the process of multi boreholes, near the borehole, a single borehole hasgreater influence on the gas pressure of coal seam. The more close to the borehole gaspressure is low. Away from the borehole, a single borehole has less influence on the gaspressure of coal seam，around the drilling area forms a centralized gas depressor area.