| Coal seam gas is one of the main hazards which Threat to mine safety. Simultaneously, Coal seam gas extraction has important value as a clean efficient energy. This article analysis of the reservoir way, migration law and output mechanism of gas inside the coal base on the structure model of pore-fissure media. This provided a theoretical basis to the building of mathematical model of loaded coal gas flow.On the basis of previous studies this paper argues that, the adsorbed Gas diffusion in coal matrix and the free state gas Seepage in coal mass fracture common components of the gas flow field. Gas seepage in coal mass fracture comply with Darcy’s law and gas migration rule in the small pores complies with the Fick’s law. Sorption-desorption dynamic balance is broken by gas flowing, coal gas in the pore system and fracture system occur mass exchange. Based on the above principle, this paper established loaded coal gas flow mathematical model on the basis of reasonable assumptions. And taking into account the effective stress change and adsorption inflation effect, this paper established dynamic evolution model of permeability and porosity.In this paper, taking raw coal containing gas as the research object, using the self-developed thermal-fluid-solid-mechanics coupling adsorption-desorption experimental system for coal containing gas, seepage desorption experiment of loaded coal containing gas was carried out, using the non-adsorption gas helium(He) calibration method to measure the porosity of loaded coal. The experiment measured the initial permeability and initial porosity of loaded coal at different adsorption balance pressures, providing the necessary parameters data for the numerical calculation of gas flow model.Comparing numerical calculation of gas flow model with experimental results for loaded coal, simulation calculating results keep good consistency with experimental data in initial porosity, initial permeability and export flow. Results show that as gas flow in the coal, the pore pressure, porosity and permeability changes dynamically, and change slow down and tend to be stable. Under the condition of low gas adsorption equilibrium pressure, as internal gas flow out, gas pressure decreases, and porosity and permeability of coal samples increases, which are verified by the experiment. However, under high gas adsorption equilibrium pressure, porosity and permeability of coal samples decrease firstly and increase afterward, showing asymmetric U-shaped variation law. The dynamic change of porosity and permeability is the result of the coupling of flow field and solid field. Therefore, when studying the gas mechanism of coal seam gas, the influence of fluid-solid coupling effect cannot be ignored. |
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