我国大部分矿区煤层渗透率较低，需要采取煤层增透措施以提高瓦斯预抽效率。超声波激励是一种高效的煤层增透技术，尤其是含水煤体在多级脉冲激励下可有效改造孔隙结构，促进瓦斯解吸。目前，多级脉冲超声波对煤体孔隙与瓦斯解吸特性影响以及不同含水率煤层超声波激励增透效果需要进一步研究。因此，本文通过实验室测试及理论分析，研究多级脉冲超声波激励对含水煤体孔隙结构及瓦斯解吸的影响规律及机理。

利用自主研发的超声波激励煤体瓦斯解吸实验系统以及低温氮吸附仪，探究了不同超声波功率和煤体饱水度条件下，煤的孔隙结构变化特征及瓦斯解吸规律。随超声波功率和煤体饱水度的增大，煤体平均孔径、比表面积和总孔容均增大，孔隙综合分形维数降低；超声波功率为1000 W时，与干燥煤体相比，煤体孔径、比表面积和总孔容相对增幅由煤体25%饱水度的0.634%、4.369%、3.504%分别增加到100%饱水度的3.199%、7.699%、8.992%，孔隙综合分形维数相对降幅从0.037%增大至0.373%。煤体瓦斯解吸量、解吸率及平均解吸速率均与超声波功率、煤体饱水度呈正线性相关；与干燥煤体相比，煤体瓦斯解吸量增幅、解吸率增幅和平均解吸速率增幅均随煤体饱水度增加呈线性增大趋势，超声波激励对饱水煤体的孔隙改造及瓦斯解吸影响效果最好。

得到超声波激励后煤体平均孔径、比表面积、总孔容、孔隙分形维数及瓦斯解吸量、解吸率、平均解吸速率随多级脉冲次数的变化关系。饱水煤体的平均孔径、比表面积、总孔容均大于超声波常规功率激励煤体，且随多级脉冲超声波次数增加呈增大趋势，孔隙分形维数随多级脉冲次数增大而减小。与超声波1000 W激励煤体相比，煤体平均孔径、比表面积和总孔容的相对增幅与多级脉冲次数呈正幂指数相关，相关系数在0.826以上；煤体瓦斯解吸量、解吸率及平均解吸速率的相对增幅与多级脉冲次数呈正线性关系，线性相关度达0.989。

揭示了多级脉冲超声波激励含水煤体瓦斯解吸机理，超声波功率逐级递增且循环作用，以水为媒介形成应力波冲击的周期性变化，促使煤体产生疲劳损伤，强化了煤的孔隙改造作用，并加剧瓦斯分子动能，进而促进煤体瓦斯解吸；提出了多级脉冲超声波发射器结合水力化技术增透煤层抽采瓦斯的方法，以期为进一步明确低渗煤层多级脉冲超声波增透技术适用性，指导相应工艺参数优化和现场应用提供一定依据。

Most of the coal seams in China's mining areas have low permeability, and measures to increase the permeability of coal seams are needed to improve the efficiency of gas pre-pumping. Ultrasonic excitation is an efficient technology to increase the permeability of coal seams, especially the water-bearing coal can effectively modify the pore structure and promote the gas desorption under multi-stage pulse excitation. At present, the influence of multi-stage pulsed ultrasonic wave on the pore space and gas desorption characteristics of coal and the effect of ultrasonic excitation on penetration enhancement of coal seams with different water content need to be further investigated. Therefore, this thesis investigates the effects of multi-stage pulsed ultrasonic excitation on the pore structure and gas desorption of water-bearing coal and the mechanism through laboratory tests and theoretical analysis.

Using the self-developed ultrasonic excitation coal gas desorption experimental system and low-temperature nitrogen adsorption instrument, we investigated the change characteristics of coal pore structure and gas desorption law under different ultrasonic power and coal water saturation conditions. With the increase of ultrasonic power and water saturation, the average pore diameter, specific surface area and total pore volume of the coal increased, and the integrated fractal dimension of the pores decreased; when the ultrasonic power was 1000 W, compared with the dry coal, the relative increase of the pore diameter, specific surface area and total pore volume of the coal increased from 0.634%, 4.369%, and 3.504% of the coal at 25% water saturation to 3.199%, 7.504% and 3.199%, respectively, of the coal at 100% water saturation. 3.199%, 7.699%, and 8.992%, and the relative decrease of pore integrated fractal dimension increased from 0.037% to 0.373%. The amount of gas desorption, desorption rate and average desorption rate of the coal were positively and linearly correlated with the ultrasonic power and the water-saturated degree of the coal; compared with the dry coal, the increase in the amount of gas desorption of the coal, the increase in the rate of desorption and the increase in the average desorption rate of the coal showed a linear trend of increase with the increase of the water-saturated degree of the coal, and ultrasonic excitation had the best effect on pore remodeling and gas desorption of the water-saturated coal.

The average pore diameter, specific surface area, total pore volume, pore fractal dimension, gas desorption volume, desorption rate and average desorption rate of the coal after ultrasonic excitation were obtained with the change of the number of multistage pulses. The average pore diameter, specific surface area and total pore volume of the water-saturated coal were larger than those of the ultrasonic conventional power-excited coal, and showed an increasing trend with the increase of the number of multistage ultrasonic pulses, and the fractal dimension of the pores decreased with the increase of the number of multistage pulses. Compared with 1000 W ultrasonic excitation, the relative increases of average pore diameter, specific surface area and total pore volume were positively correlated with the number of multistage pulses, with the correlation coefficient above 0.826; and the relative increases of gas desorption volume, desorption rate and average desorption rate were positively correlated with the number of multistage pulses, with the correlation coefficient reaching 0.989.

The mechanism of gas desorption in water-bearing coal bodies stimulated by multi-stage pulsed ultrasonic waves is revealed. The ultrasonic wave power increases step by step and acts cyclically, forming cyclic changes of stress wave impacts with water as the medium, prompting fatigue damage of the coal, intensifying the pore modification of the coal and aggravating the kinetic energy of the gas molecules, which then promotes the desorption of the gas in the coal; and the method of gas extraction in the coal beds by combining multi-stage pulsed ultrasonic emitters with the hydraulic technology for increasing the penetration of coal seams is proposed, in order to further clarify the method of gas desorption in low-permeability coal bodies. The method of multi-stage pulsed ultrasonic transmitter combined with hydraulicization technology to increase the permeability of coal seam gas extraction is proposed, which is expected to further clarify the applicability of multi-stage pulsed ultrasonic permeability technology in low-permeability coal seams, and guide the optimization of the corresponding process parameters and on-site application to provide a certain basis.

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