Power ultrasound-induced coal structure modification and desorption-diffusion kinetics evolution:Mechanisms and field applications
LIU Peng
CHEN Nan
NIE Baisheng
BAO Guangjie
ZHAO Zhengduo
LI Quangui
SONG Jibin
LIU Xianfeng
DENG Bozhi
LI Yun
ZHAO Kang
SUN Liang
LIU Wei
Abstract：To address the problem of gas extraction from soft and strongly adsorbed coal seams,the innovative idea of synergistic effect of high power ultrasonic field'mechanical vi-bration-cavitation-heat'to increase seepage and promote gas dissolution was adopted,and the research on the microscopic pore evolution and macroscopic desorption and diffusion behaviour of coal body under the excitation of ultrasonic field was carried out,and ultrasonic field seepage enhancement system device and the implementation of downhole long borehole seepage en-hancement process was developed.In addition,the engineering test of gas extraction was pro-moted by ultrasonic field excitatation of downhole along/through layer.The results indicate that after ultrasonic excitation,the maximum nitrogen adsorption capacities of Yuwu coal and Xintian coal increases from 2.314 0 and 1.661 6 cm3/g to 3.542 4 and 3.694 4 cm3/g,respec-tively,representing increases of 53.09％and 122.34％;the specific surface area is enhanced by 155.86％and 659.90％,respectively,and the pore volume increases by 66.67％and 100.00％.And the number of micropores and mesopores increases significantly and the pore struc-ture is effectively connected,which significantly improved the gas transport channels within the coal matrix.The result of gas adsorption and desorption experiments showes that the dif-fusion coefficients of the two coal samples increases from 1.76×10-8 and 8.95×10-8 m2/s to 1.99 ×10-8 and 1.05×10-7 m2/s,respectively,with an increase of 13.00％and 17.32％.The ultrasonic field excitation is sensitive to pore pressure,and the enhanced desorption effect is more significant in the low pore pressure stage.To adapt to the demand for seepage enhance-ment in soft and strongly adsorbed coal seams downhole,an 18 kW high-power ultrasonic field seepage enhancement system was developed,and a small-diameter,long borehole water-pres-sure synergistic ultrasonic segmentation seepage enhancement technology process was devel-oped.The results of the underground soft and strongly adsorbed coal seams ultrasonic seepage enhancement project tests show that after the ultrasonic excitation of the downhole borehole in the Yuwu Mine,the gas concentration increases by 101.82％～119.90％and the flow rate in-creases by 29.37％～136.72％in 30 d,and the radius of influence of the pumping promotion is up to 14 m.After ultrasonic infiltration enhancement in the hydraulic cavitation coal seam of Yuwu Coal Mine,the gas concentration increases by 5.14％～55.91％;after ultrasonic infil-tration enhancement in the penetrating borehole of Xintian Coal Mine,the gas concentration and flow rate increases by 58.35％～96.36％and 49.80％～54.57％respectively,and the ef-fective radius of pumping is more than 12 m,and the effective time of pumping is more than 60 d.In this study,microscopic,macroscopic and engineering multi-scale research were com-bined,the mechanism of ultrasonic field modified microscopic pore permeability enhancement and gas dissolution was elucidated,and the strengthening effect of pore water on ultrasonic pore expansion and permeability enhancement was revealed.This study confirms the good effect of ultrasonic field in the enhanced pumping of soft and strong adsorption coal seams,which provides an important support for the enhanced pumping of gas in soft and strongly ad-sorption coal seams.
Keywords：ultrasoundcoalgaspermeability enhancementdesorption diffusion
Publication Date：2025-09-30
Online Publishing Date：2025-10-31(First online date of this platform, not the publication date of the document)
Pages：17( 1020-1036 )