Study On The Gas Solid Coupling Model Based On Transversely Isotropic Characteristics Of Coal And Its Application

Coal is a typical sedimentary rock with transversely isotropic characteristics.The movement of gas in coal seams is a typical problem of gas solid coupling.Most of the current coal-gas coupling models are based on the assumption of coal isotropy,ignoring the transversely isotropic of coal structure.On the assumption that coal is transversely isotropic,the thesis adopted the methods of theoretical analysis,laboratory test and computer numerical simulation.The superposition relations of coal body deformation under adsorption/desorption or seepage were studied,and the deformation and permeability law of adsorbed gas considering the transverse isotropic structure characteristics of coal body were studied.Then a gas-solid coupling model which can reflect the deformation and permeability characteristics of coal body was constructed.Finally,the influence of drilling angle and spacing on extraction were studied with the gas-solid coupling model.The research is of great significance to the development of coalbed methane resources and the safety production of coal mines.The deformation mechanism of coal in the process of coal adsorption/desorption gas and gas seepage was analyzed.A method to verify the superposition relationship of coal deformation is the result of comprehensive action of adsorption expansion deformation and effective stress compression deformation was proposed.The superposition relation of coal deformation was verified by the data of CH4 and He adsorption and seepage deformation.The results showed that the average relative errors of the coal deformation of adsorption and seepage were 4.27%and 5.48%,respectively.It was verified that the deformation of coal was the result of comprehensive action of adsorption expansion deformation and effective stress compression deformation.Based on the test of isothermal adsorption of CH4 and He with vertical bedding samples of Tingnan coal mine,it was found that the deformations of coal in vertical bedding and parallel bedding direction were different under the action of gas compression,pure adsorption and both in the process of coal isothermal adsorption.The difference had nothing to do with gas pressure and the adsorbate,which was related to the nature of coal.In addition,based on the transversely isotropic characteristics of coal isothermal adsorption deformation,the isothermal adsorption deformation equation of transversely isotropic coal was deduced,and deformation equation was verified with the data of isothermal adsorption test.Taking the coal samples of Pingdingshan No.12 coal mine,Zhangcun coal mine,Tingnan coal mine and Xinjing coal mine as the research objects,the permeability tests of different bedding coal samples in different directions were carried out.The results showed that the permeability of coal was transversely isotropic,and the permeability in parallel bedding direction was similar.The permeability in parallel bedding direction was larger than that in vertical bedding direction and there were some differences between the direction of vertical bedding and parallel bedding.Based on the isothermal adsorption deformation characteristics of transversely isotropic coal,the governing equation of stress field considering transversely isotropic characteristics of coal was established.Based on the concept of structural anisotropy ratio,a permeability model considering anisotropy of coal was established.A gas-solid coupling model considering the transverse isotropy of coal was constructed with the flow equation.Finally,based on the basis of 207 working face of 4#coal seam in Tingnan coal mine,Shaanxi Province,the gas-solid coupling model considering coal transverse isotropy was used to study the influence law of the distance between boreholes and the direction of borehole layout on the pumping effect.In this thesis,the deformation of coal body was determined by the combined action of adsorption expansion deformation and effective stress compression deformation,which accorded with superposition relation.The isothermal adsorption deformation and seepage deformation of coal body were both transversely isotropic.The isothermal adsorption deformation equation and seepage equation of transversely isotropic coal were deduced,and the transversely isotropic characteristics of coal were considered.The gas solid coupling model improved the gas solid coupling theory.