我国大部分深部煤层瓦斯赋存具有高瓦斯、高应力、低渗透特征，尤其是低渗透特性，采用常规钻孔预抽煤层瓦斯效果不理想，为提高煤层瓦斯预抽率、缩短预抽时间，需对煤层采取强化增透措施，其中超声波致裂煤层增透是一种具有多种效应（空化效应、机械振动效应、热效应）耦合作用的技术，逐渐受到重视。论文采用实验及理论分析，分析超声波不同频率、时间对煤体孔隙结构损伤及渗流特性影响，研究超声波致裂作用对煤体孔隙结构损伤机理。

采用蔡司stemi508显微镜分析超声波致裂作用对煤体宏观裂隙损伤演化规律，利用盒子分形维数算法分析煤体表面裂隙分形维数特征。煤体表面裂隙宽度扩展率、分形维数增长率与致裂频率呈线性负相关；与致裂时间呈线性正相关。表明超声波致裂作用促使煤体表面裂隙扩展发育，煤体表面裂隙形态变复杂。

利用低场核磁共振技术研究超声波致裂作用下煤体内部孔隙结构演化规律。不同致裂频率、时间作用使煤体各尺寸孔隙结构、孔隙度均得到不同程度发育、贯通。煤体各尺寸孔隙增长率与致裂频率呈先增大后减小的二次函数关系，与致裂时间呈线性正相关。煤体有效孔隙度增长率、总孔隙度增长率均同致裂频率和致裂时间正相关，残余孔隙度增长率与致裂频率和致裂时间负相关。超声波频率28 kHz、35 kHz时，孔隙结构发育最为明显，煤体封闭孔隙相互贯通，内部微孔裂隙发育，自由流体空间比例增加，瓦斯抽采效率提高。致裂时间越长，孔隙结构连通性越好。

使用煤岩芯渗透率测试仪、核磁共振技术，超声波致裂作用下，煤体渗透率均得到改善。煤体渗透率变化率与致裂频率呈先增大后减小的趋势，与致裂时间呈线性正相关。致裂频率为28 kHz、35 kHz时，渗透率变化率最为明显。对比分析不同频率、时间致裂作用下煤体核磁渗透率变化率与气测渗透率变化率，渗透率变化率趋势大致相同。

通过分析超声波致裂作用下煤体宏观裂隙、内部孔隙结构与渗流特性变化相互关系，致裂频率最优范围为28 kHz~35 kHz；随着致裂时间延长，煤体孔裂隙相互贯通，改善煤体渗透率，提高瓦斯渗流能力。

论文通过多种实验手段及方法研究了超声波致裂作用对煤体孔隙结构变化及渗透特性影响规律，为提高深部低透煤层瓦斯灾害防治及煤与瓦斯安全共采提供一定理论依据和技术支持。

Most deep coal seam gas occurrence in China is characterized by high gas, high stress and low permeability, especially low permeability. The effect of pre-draining coal seam gas by conventional drilling is not ideal. In order to improve the pre-pumping rate of coal seam gas and shorten the pre-pumping time, measures should be taken to enhance the permeability of coal seam. Among them, ultrasonic is a permeability enhancement technology for fracturing coal seams under the coupling action of various effects (cavitation effect, mechanical vibration effect and thermal effect), and has gradually received attention. The paper adopts experimental and theoretical analysis, the effects of ultrasonic frequency and time on coal pore structure damage and seepage characteristics were analyzed, and the damage mechanism of ultrasonic fracturing on coal pore structure was explored.

Zeiss stemi508 microscope was used to test the damage evolution law of macro-cracks in coal body caused by ultrasonic fracturing. The fractal dimension characteristics of coal surface cracks were analyzed by box dimension algorithm. The expansion rate of coal surface fissures and the growth rate of fractal dimension of surface fissures are linearly and negatively correlated with the fracturing frequencies; but linearly and positively correlated with the fracturing time. It indicates that the ultrasonic fracturing makes the coal surface fissures more developed and the shape of the surface fissures more complex.

Low-field nuclear magnetic resonance technology was used to detect the evolution law of the pore structure inside the coal body under the action of ultrasonic fracturing. Different fracturing frequencies and time have different degrees of development and penetration of the pore structure and porosity of each size of the coal body. The pore growth rate of each size of coal body and the fracturing frequency show a quadratic function of increasing and then decreasing, and a linear positive correlation with the fracturing time. The effective porosity growth rate and total porosity growth rate of coal are positively correlated with the fracturing frequency and time, and the residual porosity growth rate is negatively correlated with the fracturing frequency and time. Under the effect of ultrasonic fracturing, the fracturing frequencies are 28 kHz and 35 kHz, and the pore structure is the most obvious. Micro-pore fractures are developed in the coal body, and the closed pores are connected with each other, the internal micro-pore fissures are developed, the proportion of free fluid space is increased, and the gas extraction efficiency is improved. As the fracturing time increases, the pore structure connectivity becomes better.

Using the coal core permeability tester and nuclear magnetic resonance technology to detect and analyze, the coal permeability has been improved under the effect of ultrasonic fracturing. The permeability change rate of coal increases first and then decreases with the fracturing frequency, and there is a positive linear correlation between the permeability change rate and the fracturing time. The rate of permeability change is most obvious when the fracturing frequencies of 28 kHz and 35 kHz. A comparative analysis of the change rate of nuclear magnetic permeability and gas permeability shows that the trend of the change rate of coal permeability under different fracturing frequency and time trends is roughly the same.

The effect of ultrasonic fracturing on the macroscopic fractures, internal pore structure and seepage characteristics of the coal body are analyzed in relation to each other. The optimal fracturing frequency range is 28 kHz to 35 kHz. As the fracturing time increases, the pores and fissures in coal body are connected with each other, which increases the permeability of coal body and improves the gas seepage capacity.

This paper studies the effect of ultrasonic fracturing on the change of pore structure and permeability characteristics of coal body by various experimental means and methods. It provides some theoretical basis and technical support for gas disaster prevention and control and safe co-mining of coal and gas in deep low-permeability coal seams.

[1]刘峰, 曹文君, 张建明, 等. 我国煤炭工业科技创新进展及“十四五”发展方向[J]. 煤炭学报, 2021, 46(1):1-15.

[2]谢和平. 深部岩体力学与开采理论研究进展[J]. 煤炭学报, 2019, 44(5):1283-1305.

[3]袁亮, 张平松. 煤炭精准开采地质保障技术的发展现状及展望[J]. 煤炭学报, 2019, 44(8):2277-2284.

[4]袁亮. 我国深部煤与瓦斯共采战略思考[J]. 煤炭学报, 2016, 41(1):1-6.

[5]何满潮. 深部的概念体系及工程评价指标[J]. 岩石力学与工程学报, 2005(16):2854-2858.

[6]谢和平, 周宏伟, 薛东杰, 等. 我国煤与瓦斯共采:理论、技术与工程[J]. 煤炭学报, 2014, 39(8):1391-1397.

[7]林海飞, 李树刚, 赵鹏翔, 等. 我国煤矿覆岩采动裂隙带卸压瓦斯抽采技术研究进展[J]. 煤炭科学技术, 2018, 46(1):28-35.

[8]付裕, 刘升贵. 宣东二矿瓦斯抽采钻孔爆破增透参数设计[A]. 北京力学会第20届学术年会论文集, 中国北京: 北京力学会, 2014: 4.

[9]张培河. 基于生产数据分析的沁水南部煤层渗透性研究[J]. 天然气地球科学, 2010, 21(3):503-507.

[10]韩金轩, 杨兆中, 李小刚, 等. 我国煤层气储层压裂现状及其展望[J]. 重庆科技学院学报(自然科学版), 2012, 14(3):53-55.

[11]周红星, 程远平, 刘洪永, 等. 突出煤层穿层钻孔群增透增流作用机制[J]. 采矿与安全工程学报, 2011, 28(4):618-622.

[12]林柏泉, 李子文, 翟成, 等. 高压脉动水力压裂卸压增透技术及应用[J]. 采矿与安全工程学报, 2011, 28(3):452-455.

[13]李波, 张路路, 孙东辉, 等. 水力冲孔措施研究进展及存在问题分析[J]. 河南理工大学学报(自然科学版), 2016, 35(1):16-22.

[14]宋维源, 王忠峰, 唐巨鹏. 水力割缝增透抽采煤层瓦斯原理及应用[J]. 中国安全科学学报, 2011, 21(4):78-82.

[15]刘健, 刘泽功, 高魁, 等. 深孔定向聚能爆破增透机制模拟试验研究及现场应用[J]. 岩石力学与工程学报, 2014, 33(12):2490-2496.

[16]张永民, 邱爱慈, 秦勇. 电脉冲可控冲击波煤储层增透原理与工程实践[J]. 煤炭科学技术, 2017, 45(9):79-85.

[17]李守国, 吕进国, 贾宝山, 等. 高压空气爆破低透气性煤层增透技术应用研究[J]. 中国安全科学学报, 2016, 26(4):119-125.

[18]Zhang L, Ye Z W, Tang J, et al. Comparative Experiment Study on Nitrogen Injection and Free Desorption of Methane-Rich Bituminous Coal Under Triaxial Loading[J]. Nephron Clinical Practice, 2017, 62(4):911-928.

[19]Xu J Z, Zhai C, Liu S, et al. Investigation of temperature effects from LCO2 with different cycle parameters on the coal pore variation based on infrared thermal imagery and low-field nuclear magnetic resonance[J]. Fuel, 2018, 215(1):528-540.

[20]余本胜, 和世超. 电磁场对煤体瓦斯流动的影响模拟分析[J]. 煤炭科学技术, 2009, 37(9):31-33+37.

[21]姜永东, 宋晓, 崔悦震, 等. 声场作用下煤中甲烷解吸扩散的特性[J]. 煤炭学报, 2015, 40(3):623-628.

[22]胡国忠, 杨南, 朱健, 等. 微波辐射下含水分煤体孔渗特性及表面裂隙演化特征实验研究[J]. 煤炭学报, 2020, 45(S2):813-822.

[23]Ye L Z, Zhu X J, Liu Y. Numerical study on dual-frequency ultrasonic enhancing cavitation effect based on bubble dynamic evolution[J]. Ultrasonics Sonochemistry, 2019, 59:104744.

[24]于国卿. 超声波对煤体孔隙结构影响规律研究[D]. 中国矿业大学, 2018.

[25]姜永东, 李业, 崔悦震, 等.声场作用下煤储层渗透性试验研究[J]. 煤炭学报, 2017, 42(S1):154-159.

[26]宋超, 姜永东, 王苏健, 等. 超声波作用下煤体微观结构的试验研究[J]. 煤炭科学技术, 2019, 47(5):139-144.

[27]Qin L, Zhai C, Liu S, et al. Changes in the petrophysical properties of coal subjected to liquid nitrogen freeze-thaw A nuclear magnetic resonance investigation[J]. Fuel, 2017, 194:102-114.

[28]Cai C Z, Gao F, Li G S, et al. Evaluation of coal damage and cracking characteristics due to liquid nitrogen cooling on the basis of the energy evolution laws[J]. Journal of Natural Gas Science and Engineering, 2016, 29:30-36.

[29]Lin H F, Li J L, Yan M, et al. Damage caused by freeze-thaw treatment with liquid nitrogen on pore and fracture structures in a water-bearing coal mass[J]. Energy Science and Engineering, 2020, 8(5):1667-1680.

[30]任韶然, 范志坤, 张亮, 等. 液氮对煤岩的冷冲击作用机制及试验研究[J]. 岩石力学与工程学报, 2013, 32(S2):3790-3794.

[31]Xu J Z, Zhai C, Ranjith P G, et al. Petrological and ultrasonic velocity changes of coals caused by thermal cycling of liquid carbon dioxide in coalbed methane recovery[J]. Fuel, 2019, 249:15-26.

[32]王兆丰, 周大超, 李豪君, 等. 液态CO2相变致裂二次增透技术[J]. 河南理工大学学报(自然科学版), 2016, 35(5):597-600.

[33]张东明, 白鑫, 尹光志, 等. 低渗煤层液态CO2相变定向射孔致裂增透技术及应用[J]. 煤炭学报, 2018, 43(7):1938-1950.

[34]卢义玉, 廖引, 汤积仁, 等. 页岩超临界CO2压裂起裂压力与裂缝形态试验研究[J]. 煤炭学报, 2018, 43(1):175-180.

[35]梁卫国, 贺伟, 阎纪伟. 超临界CO2致煤岩力学特性弱化与破裂机理[J/OL]. 煤炭学报: 1-12. DOI:10.13225/j.cnki.jccs.YG21.1899.

[36]丁洋. 低透气性煤层深孔预裂爆破增透抽采瓦斯技术研究[D]. 西安科技大学, 2013.

[37]王海东. 深部开采低渗透煤层预裂控制爆破增透机理研究[D]. 中国地震局工程力学研究所, 2012.

[38]刘健, 刘泽功, 高魁, 等. 不同装药模式爆破载荷作用下煤层裂隙扩展特征试验研究[J]. 岩石力学与工程学报, 2016, 35(4):735-742.

[39]赵善坤, 黎立云, 吴宝杨, 等. 底板型冲击危险巷道深孔断底爆破防冲原理及实践研究[J]. 采矿与安全工程学报, 2016, 33(4): 636-642.

[40]毕慧杰, 邓志刚, 苏振国, 等. 深孔爆破在小煤柱巷道顶板控制中的应用[J/OL]. 煤炭科学技术:1-8. DOI:10.13199/j.cnki.cst.2019-1421.

[41]齐庆新, 雷毅, 李宏艳, 等. 深孔断顶爆破防治冲击地压的理论与实践[J]. 岩石力学与工程学报, 2007, 26(S1):3522-3527.

[42]余永强, 杨小林, 梁为民, 等. 控制爆破致裂提高矿井瓦斯抽放率试验研究[J]. 煤炭学报, 2007, 32(4): 377-381.

[43]李春睿, 康立军, 齐庆新, 等. 深孔爆破数值模拟及其在煤矿顶板弱化中的应用[J]. 煤炭学报, 2009, 34(12):1632-1636.

[44]曹树刚, 李勇, 刘延保, 等. 深孔控制预裂爆破对煤体微观结构的影响[J]. 岩石力学与工程学报, 2009, 28(4):673-678.

[45]李树刚, 赵勇, 许满贵. 低频机械振动含瓦斯煤孔隙率方程及其试验[J]. 煤炭学报, 2016, 41(10):2612-2619.

[46]鲍先凯, 刘源, 郭军宇, 等. 煤岩体在水中高压放电下致裂效果的定量评价[J]. 岩石力学与工程学报, 2020, 39(4):715-725.

[47]林柏泉, 钟玉婷, 曹轩, 等. 循环微波辐射下煤体孔裂隙结构演化特征[J]. 西安科技大学学报, 2021, 41(6):964-972.

[48]Zhang L, Zhang C, Tu S H, et al. A study of directional permeability and gas injection to flush coal seam gas testing apparatus and method[J]. Transport in Porous Media, 2016, 111(3):573-589.

[49]Shimada S, Li H Y, Oshima Y, et al. Displacement behavior of CH4 adsorbed on coals by injecting pure CO2, N2, and CO2-N2 mixture[J]. Environmental Geology, 2005, 49(1):44-52.

[50]Mohammadian E, Junin R, Rahmani O, et al. Effects of sonication radiation on oil recovery by ultrasonic waves stimulated water-flooding[J]. Ultrasonics, 2013, 53(2):607-614.

[51]Vladimir, O, Abramov, et al. Sonochemical approaches to enhanced oil recovery[J]. Ultrasonics Sonochemistry, 2015.

[52]Mullakaev M S, Abramov V O, Abramova A V. Development of ultrasonic equipment and technology for well stimulation and enhanced oil recovery[J]. Journal of Petroleum Science and Engineering, 2015, 125:201-208.

[53]Abramov V O, Mullakaev M S, Abramova A V, et al. Ultrasonic technology for enhanced oil recovery from failing oil wells and the equipment for its implemention[J]. Ultrasonics Sonochemistry, 2013, 20(5):1289-1295.

[54]Vladimir O. Abramov a, Anna V, et al. Acoustic and sonochemical methods for altering the viscosity of oil during recovery and pipeline transportation[J]. Ultrasonics Sonochemistry, 2017, 35:389-396.

[55]Avvaru B, Venkateswaran N, Uppara P, et al. Current knowledge and potential applications of cavitation technologies for the petroleum industry[J]. Ultrasonics Sonochemistry, 2018, 42.

[56]Hamidi H, Mohammadian E , Junin R , et al. A technique for evaluating the oil/heavy-oil viscosity changes under ultrasound in a simulated porous medium[J]. Ultrasonics, 2014, 54(2):655-662.

[57]鲜学福. 我国煤层气开采利用现状及其产业化展望[J]. 重庆大学学报, 2000.

[58]马会腾, 翟成, 徐吉钊, 等. 基于NMR技术的超声波频率对煤体激励致裂效果的影响[J]. 煤田地质与勘探, 2019, 47(4): 38-44.

[59]Tang Z Q, Zhai C , Zou Q L, et al. Changes to coal pores and fracture development by ultrasonic wave excitation using nuclear magnetic resonance[J]. Fuel, 2016, 15:571-578.

[60]Shi Q M, Qin Y, Li J Q, et al. Simulation of the crack development in coal without confining stress under ultrasonic wave treatment[J]. Fuel, 2017, 205:222-231.

[61]肖晓春, 潘一山, 吕祥锋, 等. 超声激励低渗煤层甲烷增透机理[J]. 地球物理学报, 2013, 56(5):1726-1733.

[62]Shi Q M, Qin Y, Zhou B Y, et al. Porosity changes in bituminous and anthracite coal with ultrasonic treatment[J]. Fuel, 2019, 255,115739

[63]田洪波, 蒋曙光, 李玥, 等. 功率声波激励下无烟煤孔隙变化及裂隙发育研究[J]. 煤矿安全, 2017, 48(8): 9-12.

[64]王云刚, 李满贵, 陈兵兵, 等. 干燥及饱和含水煤样超声波特征的实验研究[J]. 煤炭学报, 2015, 40(10):2445-2450.

[65]范翔宇, 段美恒, 张千贵, 等. 页岩层理与含水率对声波传播影响的实验研究[J]. 西南石油大学学报(自然科学版), 2017, 39(2):53-61.

[66]Sahinoglu E, Uslu T. Effects of various parameters on ultrasonic comminution of coal in water media[J]. Fuel Processing Technology, 2015, 137:48-54.

[67]Rossat M, Chaix J F, Garnier V. Ultrasonic wave propagation in heterogeneous solid media[J]. Journal of the Acoustical Society of America, 2016, 123(5):3844.

[68]易俊. 声震法提高煤层气抽采率的机理及技术原理研究[D]. 重庆大学, 2007.

[69]Jiang Y D, Son X, Liu H, et al. Laboratory measurements of methane desorption on coal during acoustic stimulation[J]. International Journal of Rock Mechanics & Mining Sciences, 2015, 78:10-18.

[70]卢义玉, 王景环, 黄飞, 等. 空化水射流声震效应促进瓦斯解吸渗流测试装置的改进[J]. 煤炭学报, 2013, 38(9):1604-1610

[71]李晓红, 冯明涛, 周东平, 等. 空化水射流声震效应强化煤层瓦斯解吸渗流的实验[J]. 重庆大学学报, 2011, 34(4): 1-5.

[72]赵丽娟. 超声波作用下的煤层气吸附一解吸规律实验[J]. 天然气工业, 2016, 36(2):21-25.

[73]于永江, 张春会, 王来贵. 超声波干扰提高煤层气抽放率的机理[J]. 辽宁工程技术大学学报(自然科学版), 2008, 27(6):805-808.

[74]于国卿, 翟成, 秦雷, 等. 超声波功率对煤体孔隙影响规律研究[J]. 中国矿业大学学报, 2018, 47(2):264-270+322.

[75]Zhang J W, Li Y L. Ultrasonic vibrations and coal permeability: Laboratory experimental investigations and numerical simulations[J]. International Journal of Mining Science and Technology, 2017, 27(2):221-228.

[76]秦雷. 液氮循环致裂煤体孔隙结构演化特征及增透机制研究[D]. 中国矿业大学, 2018.

[77]徐吉钊. 液态CO2循环冲击致裂煤体孔隙结构及损伤力学特征研究[D]. 中国矿业大学, 2020.

[78]郭继胜. 不同液氮注射参量对煤体致裂效果影响规律的研究[D]. 中国矿业大学, 2020.

[79]B . B .霍多特著, 宋士钊, 王佑安. 煤与瓦斯突出[M]. 中国工业出版社, 1966.

[80]Cai Y D, Liu D M, Pan Z J, et al. Petrophysical characterization of Chinese coal cores with heat treatment by nuclear magnetic resonance[J]. Fuel, 2013, 108:292-302.

[81]Li H, Lin B Q, Chen Z W, et al. Evolution of coal petrophysical properties under microwave irradiation stimulation for different water saturation conditions[J]. Energy & Fuels, 2017, 31(9):8852-8864.

[82]严敏, 张一真, 林海飞, 等. 液氮浸融对不同预制温度煤体损伤特性试验研究[J]. 煤炭学报, 2020, 45(8):2813-2823.

[83]姜鹏, 郭和坤, 李海波, 等. 低渗透率砂岩可动流体T2截止值实验研究[J]. 测井技术, 2010, 34(4): 327-330.

[84]Ou Y Z, Liu D M, Cai Y D, et al. Fractal Analysis on Heterogeneity of Pore-Fractures in Middle-High Rank Coals with NMR[J]. Energy & Fuels, 2016, 30(7): 5449-5458.

[85]Cai Y D, Liu D M, Pan Z J, et al. Petrophysical characterization of Chinese coal cores with heat treatment by nuclear magnetic resonance[J]. Fuel, 2013, 108(11):292-302.

[86]Yao Y B, Liu D M, Yao C, et al. Petrophysical characterization of coals by low-field nuclear magnetic resonance (NMR)[J]. Fuel, 2010, 89(7):1371-1380.

[87]Kenyon W E, Day P I, Straley C, et al. A Three-Part Study of NMR Longitudinal Relaxation Properties of Water-Saturated Sandstones[J]. SPE Formation Evaluation, 1988, 3(3):622-636.

[88]Westphal H, Surholt I, Kiesl C, et al. NMR Measurements in Carbonate Rocks: Problems and an Approach to a Solution[J]. Pure and Applied Geophysics, 2005, 162(3):549-570.

[89]Yao Y B, Liu D M, Liu J G, et al. Assessing the Water Migration and Permeability of Large Intact Bituminous and Anthracite Coals Using NMR Relaxation Spectrometry[J]. Transport in Porous Media, 2015, 107(2):527-542.

[90]Talabi O, Alsayari S, Iglauer S, et al. Pore-scale simulation of NMR response[J]. Journal of Petroleum Science & Engineering, 2008, 67(3):168-178.

[91]Ye L Z, Zhu X J, Liu Y. Numerical study on dual-frequency ultrasonic enhancing cavitation effect based on bubble dynamic evolution[J]. Ultrasonics Sonochemistry, 2019, 59:104744.

[92]Dimitriadou E , Raftopoulou M , Kasapidou P M , et al. Ultrasound promoted synthesis of chromeno[2,3-b]pyridines and their evaluation as lipid peroxidation inhibitors[J]. Archive for Organic Chemistry, 2014:372-384.

[93]邝生鲁, 贡长生. 声化工研究进展[J]. 现代化工, 1989, 9(6): 23-26.