Numerical Simulation And Application Of Parameter Optimization Of Carbon Dioxide Phase Change Cracking Control Hole

As a new type of coal seam pressure relief and permeability increasing technology,carbon dioxide phase transformation cracking technology has a wide range of application and good cracking effect.In this paper,theoretical analysis and numerical simulation are used to study the mechanism of the control pore in the phase transformation cracking of carbon dioxide.The main research contents and conclusions are as follows:(1)Based on the analysis of the basic principle of carbon dioxide phase transformation cracking technology,the process of carbon dioxide phase transformation cracking is divided into high pressure gas action stage and stress wave action stage.The TNT equivalent of CO2 transformation induced cracking was calculated and the relationship between pressure and time was analyzed.In this paper,the mechanical effect of the controlled pore in the stage of stress wave action in the process of phase change induced cracking is studied,and the influence range of the crushed and fractured areas with controlled pore is analyzed.(2)The coupling mathematical model of solid and gas of coal body cracked by carbon dioxide transformation is established.The parameters of control hole are introduced into the effective stress equation.The mathematical model of damage evolution of coal body is represented by the deformation field equation,element damage equation and permeability equation of coal body with control hole.Combined with the equations of gas migration,mass conservation and energy conservation in coal seam,a coupling mathematical model of solid and gas in coal seam caused by carbon dioxide with effective force of control pore is established.(3)COMSOL numerical simulation is carried out to simulate the process of cracking caused by carbon dioxide transformation.The influence of the same cracking pressure on different mechanical properties of coal and rock masses and the influence of different cracking pressure on the same coal body are simulated.The influence of different positions of control holes on the cracking effect and the influence law of different hole diameters on cracks are simulated.The results show that the radius of the control hole is 10.2%larger than that of the crack area without the control hole,and the effect of setting the control hole at the boundary of the crack area and the stress disturbance area is the best.The crack with larger control hole diameter develops faster and the influence range of the crack network is wider.(4)Through the field application of the technology,the results show that the effective influence radius of carbon dioxide phase change cracking is 5m?6m,which is similar to the numerical simulation results.It shows that the technology can effectively improve the permeability of coal seam,improve the gas concentration and gas extraction.The results can provide a new analytical method for optimizing the parameters of control holes in the process of carbon dioxide transformation induced cracking,and enrich the basic theoretical research of carbon dioxide transformation induced cracking.