Research On Numerical Simulation Of Fluid-solid And Field Application For Coalbed Methane Recovery

Coal mine gas hazards is one of the main factors that disturbed mine safety production.Gas extraction can effectively reduce the gas content of coal seam and provide safety producted circumstance of mine.With the deeper exploitated of coal mining in China,gas content coalbed was presented by soft and larger gas pressure,which induced the drilling hole of soft coal seam collapsed easily in the process of gas extraction resulting the gas extraction efficiency was decreased.In this paper,mainly based on the characteristics of the creep deformation around the boreholes of coal seam,combined the experimental investigation,theoretical analysis,numerical simulation and filed application methods to improved methane extraction parameters,then a filed application was developed that based on the optimizated parameters,furthermore the gas extraction efficiency was tested at the same time.The stress-strain law and lateral deformation characteristics of coal body are analyzed by the mechanical properties of soft and hard coal.The failure process of hard coal body failure is characterized by elastic-brittle deformation,and the failure process of soft coal is characterized by plastic deformation and volume expansion,the internal structure of coal body,especially the development degree of pore fissure,is the main influencing factor.Based on the experimental results,the creep characteristics of coal containing gas are analyzed and the deformation control equations of the coal body around the borehole are obtained.Based on the gas seepage equation and the coal deformation control equation,a fluid-solid coupling mathematical model considering the creep characteristics of coal is established by considering the permeability dynamic evolution model under the action of matrix shrinkage and effective stress.The gas extraction process is simulated by COMSOL Multiphysics software,and the relationship between the optimum spacing of holes and the effective radius of gas extraction is obtained through the simulation results,and the optimum spacing between holes is 3.2-4.2 m;The mathematical model of stress variation around the roadway was established,and the numerical simulation analysis of the stress around the roadway was carried out on the basis of the mathematical model.The rational sealing depth of the tunnel was determined to be 12 m.According to the mathematical model of fluid solid coupling,the reasonable pre pumping period of gas was simulated to be 180 d.According to the simulation results that optimized and changed some parameters and tested the gas extracted efficiency of working face result of testing and optimizing parameters conforms to various standards,and it can reduce the number and the total length of 25%of drilling holes,shorten the gas extraction period(i.e.,reduced by 30 days),the arrangement of boreholes not only ensure the coal mine have a safety production environment but also reduced drilling construction quantity,meanwhile the economic benefit enhanced obviously.