Research On Dynamic Coupling Model And Its Application Base On The Pore-fracture Dual Media Characteristics Of Coal Containing Gas

Gasextraction is the main technical means to governance gas accident,it can efficiently eliminatethe risk of gas outburst,and use the gas as the clean energy at same time.In order to get the optimal extraction design and the best extraction effect,on the basis of previous researches,this paper based on the characteristics of pore-fracture double medium,analysised the different occurrence forms,migration mechanism and output mode of gas,it set up the dual medium dynamic coupling model.And research the change law of gas pressure and permeability by 3D numerical simulation,andanalyze the influence factors about gas extraction.It also determined the reasonable boreholes spacing and can give a certain guiding significance for the gas extraction.Analysising the desorption-diffusion-seepage’s flow mechanism of gas which in the coal seam,because of the gas seepage’s speed is faster than thediffusion’s speed,it lead to thedifferential pressure between pore’s and fracture’s system,so the coal matrix began desorbingthe gas,and the dual medium gas flow control equation has built by the matrix exchange capacity.Considering the comprehensive influence of geostress,gas pressure and matrix shrinkage on coal’s permeability,which the effective stress and matrix shrinkage effect different mechanism on the pore system and fracture system,the permeability dynamic evolution model is obtained.Regard for the gassy coal-rock as elastic-plastic body and built the the coal-rock deformation control equation by the elastic-plastic constitutive relation,equilibrium equation and the geometric equation.All above these equations constituted the dual medium dynamic coupling model of coal containing gas.Embeddingthe mathematical model to COMSOL Multiphysicsthe,and built the 3D model of gas drainage borehole,it used to research the gas extraction effect by numerical simulation.Then use the pressure drop method for field test,whichresults are basically coincided with simulation results,and verified the reliability of 3D numerical simulation which based on pore-fracture dual medium dynamic coupling model,so,the results in this paper can meet the standards of the actual extraction work.