Study On Microstructure Fine Characterization And Desorption And Seepage Characteristics Of Coal Body Under Ultrasonic Incentive

In order to reveal in depth the mechanism of the sound field to improve the extraction rate of methane,the paper used CT,low temperature nitrogen absorption,NMR and FIB-SEM methods to fine characterize the microstructure of coal before and after ultrasonic incentive.Using the self-designed experimental system of methane adsorption,desorption and seepage under ultrasonic incentive,the desorption and diffusion characteristics of methane in coal under different powers ultrasonic incentive,and the characteristics of methane seepage in coal under stress field,pore pressure and ultrasonic were studied experimentally.The mechanism of improving the permeability of coal seam and promoting the desorption and diffusion of methane by sound field is discussed.The main conclusions are as follows:?1?Ultrasonic vibration effects,cavitation effects,and thermal effects can change the structure of the coal body.The CT scan results show that the ultrasonic incentive causes the coal body to be partially damaged,and new cracks are generated,the original crack channel is cleaned and the coal seam connectivity is increased.The results of low temperature nitrogen absorption show that the isothermal adsorption/desorption curves of coal samples before and after ultrasonic incentive are consistent,and the N₂adsorption amount,average pore size,specific surface area and pore volume of coal increase with the increase of ultrasonic power.The NMR results show that the coal sampleafter the ultrasonic incentive,the peak value of the T₂ curve increases,the pore crack increases,the imaging pixel points increase rapidly,the connectivity range expands,and the interpenetrating fractures are formed,indicating that the ultrasonic has caused damage to the internal microstructure of the coal sample.The FIB-SEM results show that there are closed pores in the coal,closed pores and through pores constitute the internal pores of the coal body,the 3D model of coal structure is established by using the three-dimensional reconstruction software Avizo.?2?The desorption and diffusion laws of methane in coal before and after ultrasonic incentive are basically the same.The total desorption of methane in coal under ultrasonic incentive is larger than that without ultrasonic,and increases with the increase of ultrasonic power.The diffusion model can better describe the desorption characteristics of methane in coal,and the saturation desorption parameter of the model increases linearly with the increase of power.Under the ultrasonic incentive,the diffusion coefficient of coal increases and the diffusion capacity increases,indicating that ultrasonic can promote the desorption and diffusion of methane.?3?Experiment studied on the law of seepage in coal under stress field,pore pressure and ultrasonic.It is concluded that the permeability of coal decreases with a negative exponential function as the average effective stress increases.Under the same conditions,the permeability of coal increases under ultrasonic incentive,and the permeability of coal increases with the increase of ultrasonic incentive time.After 2.5hours of ultrasonic action,the permeability of coal tends to be stable,indicating that ultrasonic wave can increase the permeability of coal.