Research On The Damage And Degradation Law And Seepage Mechanism Of Gas-containing Coal Roc

Coalbed methane as a companion in the process of coal formation,is a clean energy with great development potential,and at the same time,it is also a prerequisite for coal mine power disasters.With the gradual extension of coal mining to the deep,the coal seam occurrence environment is facing problems such as complex geological structure,high geostress,high gas pressure and low permeability.In the process of coalbed methane extraction and underground coal mining,the stress state and seepage behavior of coal and rock will change significantly compared with the original state.Especially,with the increase of coal mining depth,the coal in front of the working face are prone to plastic deformation or even instability under the action of supporting pressure,which leads to the complexity of coal mechanical characteristics and gas flow law,thus greatly increasing the possibility of coal and gas outburst accidents.Therefore,it is of great practical significance to study the deformation characteristics of coal and the law of gas seepage in the process of coalbed methane extraction and underground coal mining to ensure the safe and efficient production of coal mines.The coal samples studied in this paper are taken from K₂coal seam of Songzao coal mine in Chongqing and No.3 coal seam of Zhaozhuang coal mine in Jincheng,Shanxi,and the pore pressure seepage test under constant external stress（simulating coalbed methane extraction）and triaxial compression-seepage test under different confining pressures and different gas pressures（simulating underground coal mining）are carried out respectively.The mechanical response and seepage characteristics of coal in elastic stage and damage fracture process are respectively proved,and the influence mechanism of adsorption-load coupling on damage-seepage characteristics of coal is clarified.The main research progress is as follows:（1）Analyze the coal permeability evolution law in the process of pore pressure reduction,and based on the scientific hypothesis that matrix shrinkage and effective stress increase caused by pore pressure decrease have competing effects on permeability,the dominant factors of permeability evolution on both sides of critical pore pressure are discussed.Based on the deformation theory of porous elastic medium,the coal permeability model under the change of pore pressure is deduced.The rationality of the model is verified by experimental data,and the characteristics of gas seepage during coalbed methane extraction are revealed.（2）The characteristics of deformation and failure stage and damage evolution law of coal under different confining pressure and gas pressure are analyzed,and the influence law of confining pressure and gas pressure on the change of physical and mechanical parameters of coal is expounded,and the cooperative response mechanism between damage evolution and permeability change in the process of whole stress strain is further analyzed.Reveal the deterioration mechanism of gas on coal strength,and discuss the influence of gas pressure change on reservoir stability under in-situ conditions.（3）The expression of total damage variables of coal under the coupling of gas adsorption and stress loading is derived,and the damage constitutive model of coal is established under the framework of elastic-plastic mechanics.The permeability jump coefficient is introduced to describe the sudden increase of permeability after coal damage and fracture,and a damage-permeability model based on elastic-plastic deformation is further constructed.The rationality of the established constitutive model and damage-permeability model is verified by the experimental data under different gas pressure conditions,which shows that the established model can well describe the deformation characteristics of coal and the gas seepage law during underground mining of coal mines.