我国大部分矿区煤层渗透性偏低，常规钻孔预抽效果较差，需进行煤层增透瓦斯抽采。脉冲超声波（>20kHz）增透技术具备安全高效、绿色可靠等优点，可有效改善煤层孔隙裂隙，提高渗透率，实现煤层瓦斯高效抽采。本文通过实验测试与理论分析，研究不同超声波脉冲频数、脉冲功率对煤体孔隙裂隙结构发育及渗流特性演化的影响规律。

利用核磁共振成像分析仪，分析不同超声波脉冲频数、脉冲功率激励下煤体孔隙结构变化规律，得到随脉冲频数、脉冲功率增大，总孔隙率变化量、总孔隙率变化率、有效孔隙率变化量、有效孔隙率变化率均增大，残余孔隙率变化量、残余孔隙率变化率均减小；当脉冲功率500 W-50 W时，脉冲频数16次与1次相比，总孔隙率变化量、有效孔隙率变化量分别增大1.77倍、1.90倍，残余孔隙率变化量减小2.26倍；当脉冲频数16次时，脉冲功率500 W-450 W与500 W-50 W相比，总孔隙率变化量、有效孔隙率变化量分别增大1.46倍、1.43倍，残余孔隙率变化量减小1.37倍。

通过非金属超声波检测分析仪，分析不同超声波脉冲频数、脉冲功率激励下煤体纵波波速衰减规律与微观损伤程度，得到随脉冲频数、脉冲功率增大，纵波波速衰减量、纵波波速衰减率及微观损伤率均增大；当脉冲功率500 W-50 W时，脉冲频数16次与1次相比，纵波波速衰减量、纵波波速衰减率及微观损伤率分别增大1.25倍、1.25倍、1.24倍；当脉冲频数16次时，脉冲功率500 W-450 W与500 W-50 W相比，纵波波速衰减量、纵波波速衰减率及微观损伤率分别增大1.15倍、1.15倍、1.13倍。

采用蔡司光学体视显微镜，分析不同超声波脉冲频数、脉冲功率激励下煤体表面裂隙面积变化规律，得到随脉冲频数、脉冲功率增大，表面裂隙面积拓展率、表面裂隙分形维数变化率均增大；当脉冲功率500 W-50 W时，脉冲频数16次与1次相比，表面裂隙面积拓展率、表面裂隙分形维数变化率分别增大2.85倍、16.45倍；当脉冲频数16次时，脉冲功率500 W-450 W与500 W-50 W相比，表面裂隙面积拓展率、表面裂隙分形维数变化率分别增大2.83倍、3.64倍。

利用煤岩芯渗透率测定仪，研究不同应力环境条件、超声波脉冲频数、脉冲功率激励下煤体渗流特性演化规律，得到随围压、有效应力增大，激励前后气测渗透率均减小，且均符合指数函数关系；随进气压力增大，激励前后气测渗透率均增大，且均符合幂函数关系。随脉冲频数、脉冲功率增大，气测渗透率均增大；以轴压4.5 MPa、围压3 MPa、进气压力1.1 MPa、出气压力0.1 MPa、有效应力为2.9 MPa为例，当脉冲功率500 W-50 W时，脉冲频数16次与1次相比，气测渗透率变化量、变化率分别增大9.59倍、9.19倍；当脉冲频数16次时，脉冲功率500 W-450 W与500 W-50 W相比，气测渗透率变化量、变化率分别增大1.24倍、1.28倍。

分析脉冲超声波激励下煤体渗流特性与孔隙裂隙结构参数的影响关系，得到随脉冲频数、脉冲功率增大，微小孔、中孔、大孔数量均有所增加，孔隙连通性显著增强，煤层渗透率明显提高；提出脉冲超声波增透煤体的技术思路，为进一步明确脉冲超声波增透技术的适用范围，以及优化工艺参数与指导现场应用提供一定依据。

The permeability of coal seams in most mining areas in China is low, and the pre-pumping effect of conventional drilling is poor, so it is necessary to carry out coal seam enhancement gas extraction. Pulsed ultrasonic (>20 kHz) enhancement technology has the advantages of safety, high efficiency, green and reliable, which can effectively improve the pore fracture of the coal seam, increase the permeability, and realize the efficient extraction of coal seam gas. In this paper, the influence of different ultrasonic pulse numbers and pulse powers on the development of pore and fracture structure and the evolution of seepage characteristics of coal is investigated through experimental tests and theoretical analysis.

Using nuclear magnetic resonance imaging analyzer, analyze the change rule of coal pore structure under different ultrasonic pulse numbers and pulse powers excitation, and get that with the increase of pulse numbers and pulse powers, the amount of total porosity change, the total porosity change rates, the amounts of effective porosity change, the effective porosity change rates increase, and the amounts of residual porosity change, and the residual porosity change rates decrease; when the pulse powers of 500 W-50 W, pulse numbers 16 times compared with 1 time, the amounts of total porosity change, effective porosity change increased by 1.77 times, 1.90 times, respectively, and the amounts of change in residual porosity decreased by 2.26 times; when the pulse numbers 16 times, the pulse powers 500 W-450 W compared with 500 W-50 W, the amounts of total porosity change, effective porosity change increased by 1.46 times, 1.43 times, respectively, and the amounts of change in residual porosity change decreased by 1.37 times.

Through the non-metallic ultrasonic detection analyzer, we analyzed the longitudinal wave velocity attenuation law and microscopic damage degree of coal under different ultrasonic pulse numbers and pulse powers excitation, and obtained that the longitudinal wave velocity attenuation amounts, the longitudinal wave velocity attenuation rates and the microscopic damage rates increased with the increase of pulse numbers and pulse powers; when the pulse powers were 500 W-50 W, the longitudinal wave velocity attenuation, longitudinal wave velocity attenuation rates and microscopic damage rates increased 1.25 times, 1.25 times and 1.24 times, respectively; when the pulse frequency number 16 times, the pulse powers 500 W-450 W were compared with 500 W-50 W, the pulse frequency numbers 16 times was compared with 1 time, the longitudinal wave velocity attenuation amounts, longitudinal wave velocity attenuation rates and microscopic damage rates increased 1.15 times, 1.15 times and 1.13 times, respectively.

Using Zeiss optical stereo microscope, we analyzed the change rule of the surface fracture areas of the coal under different ultrasonic pulse numbers and pulse powers, and obtained that the expansion rates of the surface fracture areas and the change rates of the fractal dimensions of the surface fracture increased with the increase of the pulse numbers and pulse powers; when the pulse powers were 500 W-50 W, the pulse number 16 times compared with 1 time, the surface fracture areas expansion rates, surface fractal dimension change rates increased 2.85 times, 16.45 times, respectively; when the pulse numbers were 16 times, the pulse powers 500 W-450 W compared with 500 W-50 W, the surface fracture areas expansion rates and the change rates of the fractal dimensions of the surface fracture increased by 2.83 times and 3.64 times, respectively.

Using the coal core permeability tester, we studied the evolution law of seepage characteristics of coal under different stresses of environment conditions, ultrasonic pulse numbers and pulse powers, and obtained that with the increase of the perimeter pressures and effective stresses, the gas permeability before and after the excitation decreased, and all of them were in line with the exponential function; with the increase of inlet pressures, the gas permeability before and after the excitation increased, and all of them were in line with the power function relationship; The gas permeability increases with pulse numbers and pulse powers; taking the axial pressure of 4.5 MPa, peripheral pressures of 3 MPa, inlet pressures of 1.1 MPa, outlet pressures of 0.1 MPa, and effective stresses of 2.9 MPa as an example, when the pulse powers of 500 W-50 W are used, the gas permeability increases with pulse numbers of 16 compared with 1, the gas permeability increases with the amounts of change, and the rates of change by 9.59 times and 9.19 times, respectively; when the pulse numbers 16 times, the pulse powers 500 W-450 W compared with 500 W-50 W, the gas permeability increases in the amounts and rates of change by 1.24 times and 1.28 times, respectively.

Analyze the relationship between the seepage characteristics of coal and the pore and fracture structure parameters under pulse ultrasonic excitation, and get that with the increase of pulse numbers and pulse powers, the numbers of micro-small pores, medium pores and large pores increase, the pore connectivity was significantly enhanced, and the permeability of the coal seam was obviously increased; put forward the technical ideas of pulse ultrasonic enhancement of coal, and provide some bases for the further clarification of the scope of application of pulse ultrasonic enhancement technology, as well as for the optimization of process parameters and guiding field application.