Simulation Study of Coal Seam Gas Extraction Characteristics Based on Coal Permeability Evolution Model under Thermal Effect.

The permeability evolution law of high temperature and high stress coal seam is determined by the influence of multiphase coexistence and multifield coupling. In an environment greatly affected by disturbance and high temperature, the coal permeability model under the coupling of thermal and mechanical creep is not only a vital framework from which to examine gas migration law in multiphase and multifield coal seams but also an important theoretical foundation for gas control in coal seams. The influence of high-temperature environment on creep deformation and permeability is analyzed by several creep seepage tests under different temperature conditions.A mathematical model for the evolution of coal permeability considering the influence of temperature is established through the theory of matrix-crack interaction based on gas adsorption and desorption and thermal expansion deformation. Based on the permeability model under the coupling of thermal and mechanical creep, the numerical model of gas migration, seepage field, diffusion field, stress field, and temperature field is constructed, and the law of gas migration in coal seam under multifield coupling is explored. The influence law of thermal effect on gas extraction characteristics is analyzed, in which the time-varying mechanism of temperature field, the relationship between creep deformation and temperature and pressure, the influence of creep deformation on permeability, the dynamic distribution of gas pressure, and the change of gas extraction quantity are described in detail. It is concluded that the influence of temperature on permeability is much greater than that of creep deformation and that a high initial coal seam temperature is beneficial to gas extraction. It provides theoretical basis and technical guidance for the study of multifield coupled gas migration and coal seam gas treatment.