【作者】 周东平；

【导师】 李晓红；

【作者基本信息】 重庆大学 ， 采矿工程， 2010， 博士

【摘要】 随着煤矿开采深度的越来越大,含瓦斯煤层微孔隙、低渗透性、高吸附的赋存特征越来越显现出来,在实施“先抽后采”的煤及煤层瓦斯井下双能源开采过程中,瓦斯难以抽采所导致的煤矿瓦斯事故、环境污染和能源浪费等问题是困扰煤矿生产的主要问题。国内外专家对煤层气开采激励技术进行了相当广泛的研究,其强化措施主要包括煤层造穴、水力压裂、注气和物理场激励等。声震法是一种有效的强化提高煤层气抽采率的技术,可控声震法在现场的应用工艺还不够成熟,难以推广。但是利用高压水射流割缝卸压技术在现场的应用已经比较成熟,现场应用较为广泛,这种淹没状态下的水射流往往会发生空化现象,空泡的溃灭会产生巨大的空化噪声,目前国内外对利用此空化效应所产生的噪声波促进煤层瓦斯解吸渗流的研究还处于空白。本文结合国内外在低透气性煤层强化煤层瓦斯抽采的研究现状,依托国家自然科学基金委员会专项创新群体基金项目“高压水射流破岩理论及其在地下工程中的应用基础研究”(项目编号:50621403,50921063),以西南地区煤矿为研究对象,运用实验研究、理论推导和数值模拟相结合的方法研究了空化水射流空化效应产生机理、空化噪声频谱特性、传播衰减和热效应,并进行了空化效应促进煤层瓦斯解吸渗流的实验研究,最后研究了空化水射流空化声震作用下煤层瓦斯解吸渗流机理和现场应用。本文所研究内容及获得的结论主要包括以下几个方面:①对空化效应产生的可视化实验和数值模拟研究表明,空化水射流空泡云的发育过程都经历了空泡云的膨胀、压缩、再膨胀、压缩、溃灭的几个过程。缩放型喷嘴中空化产生点在喉管和扩散段边界层的位置,在有悬浮物的具有一定速度的淹没液中,空化则发生在与速度垂直的悬浮物两侧。上述两种方法所获得的空泡云与泵压、围压的关系是相吻合的:空泡的产生随射流泵压和围压而变化,泵压越大,空化效果越明显,围压对空泡的产生存在最佳值。②通过对空泡溃灭的噪声波的频谱特性的研究,得到空化噪声波可以用单指数模型、双指数模型以及脉冲序列模型来表示,但脉冲序列模型能够更好的表示空化噪声波的特性。噪声波在煤层中传播将会导致煤层温度升高,从而促进煤层瓦斯解吸渗流。③对空化水射流的空化振动测试实验表明,空化现象发生以后,气穴溃灭时噪声振动的频段很宽,在2000-10000Hz,说明空化腔中空化气泡半径在尺度上有很大差异,振动在5400-6800Hz之间出现了一段振动频率的峰值,说明气泡在此溃灭半径范围内的存在更加集中。振动频率越集中,对煤层瓦斯解吸渗流影响更加显著。④对空化水射流的空化效应促进煤层瓦斯解吸的实验研究表明,空化效应的产生对煤层瓦斯解吸渗流都有促进作用。与未加空化效应的煤样解吸相比,当施加空化数为0.0038的空化声震时,煤样解吸时间缩短16.4%,解吸量增加率为22.6%。⑤通过对煤层吸附瓦斯的微观特性和空化声震促进煤层瓦斯解吸渗流的机理研究表明,吸附势垒是由煤大分子结构和瓦斯气体的性质决定的,瓦斯分子的吸附势垒越深,脱附时需要的能量越大,吸附量就越大,而脱附所需要的能量由气体分子的碰撞或升高温度来提供,为了能够离开煤的表面,解吸成为自由气体,瓦斯气体分子必须至少获得吸附时损失的那部分能量才能脱离煤体的作用。空化声震主要是通过机械振动效应、热效应和致裂损伤效应来促进煤层瓦斯解吸渗流的。空化声震的施加,机械振动效应降低了煤层骨架应力,致裂损伤效应提高煤层的孔隙度,煤层系统温度的升高提供了煤层瓦斯解吸的活化能,它们共同作用强化了煤层瓦斯的解吸渗流。⑥现场试验表明,利用高压水射流钻孔割缝及空化声震强化瓦斯解吸后,单孔最高瓦斯抽采浓度提高27.3倍,最高纯瓦斯抽放量提高15倍。与相同赋存条件下的石门揭煤工程相比,其瓦斯预抽时间降低45.27%。瓦斯预抽钻孔数量减少30.5%,钻孔进尺减少33.7%。本论文的主要创新之处在于:①首次进行了高压水射流空化现象全过程的可视化研究,确定了泵压、围压对空化效应的影响规律,揭示了空泡云的孕育、发展、溃灭机理及聚能特征。②创新性地提出将高压水射流空化声震效应用于强化煤层瓦斯解吸渗流进而提高煤层瓦斯抽采率的新思路,利用自行研制的空化声震促进煤层瓦斯解吸渗流实验装置,建立了空化水射流参数与煤层瓦斯解吸渗流之间的关系模型。③确立了空化噪声波频谱特性优化描述模型及传播衰减规律,得出了空化噪声波温度效应的能量方程及机械振动效应的致裂损伤模型,揭示了空化水射流声震效应促进煤层瓦斯解吸渗流机理,为高压水射流空化效应促进煤层瓦斯解吸渗流的理论研究及工程应用奠定了理论和实验基础。更多还原

【Abstract】 With the increasing depth of coal mining,the intrinsic properties of coal seams (micro-porosity, low permeability and high adsorption) become more apparent. It’s difficult to execute gas drainage in the process of coal-gas dual-energy mining, which often causes ethane explosion, environment pollution and energy wasting. So far, many techniques have been studied to improve gas drainage, such as caving, hydraulic fracture, CO2 injection and physical field excitation. Sonic vibrating method is deems as promising, it can increase the methane drainage rate efficiently; however, it is hard to further promote for it’s immature technical process. Thanks to the technology of water jet with high pressure, this problem can be solved effectively, because cavitation water jet in the situation of submergence can produce noise when bubble collapse, and this noise can promote methane desorption and seepage. No research has been reported about how sonic vibrating of cavitation water jet promotes methane desorption and seepage although this technology has been widely adopted in coal seams slotting.In the paper, the mechanism of cavitation, spectral characteristics of cavitation noise, propagation model and heat effect are researched by lab experiment, theoretic analysis and numerical simulation, then how cavitation promotes the methane desorption and seepage is studied via experiment.Finally, the mechanism of gas desorption and seepage under sonic vibrating of cavitation water jets and field test is studied theoretically., some conclusions are arrived as follows.①The growth of bubble cloud includes swelling and compressing, reinflating and recompressing, collapsing and falling in the cavitation water jets. Cavitation develops on the boundary layer between throat and diffusion section of Convergent-divergent nozzle. In the submerged suspended-particulate, cavitation develops on both sides of suspended-solid at vertical speed orientation. The result of numerical simulation is close to that of experimental method: The cavitation bubble changes with pump pressure and confining pressure, larger the pump pressure is, cavitation develops more obviously; and suitable confining pressure could produce the perfect bubble.②The noise of bubble collapse can be described by single index model, double exponential model or pulse sequence model, but the pulse sequence model can better express the characteristics of cavitation noise waves. Propagation of noise will raise coal temperature and promote methane desorption and seepage.③The experiment of vibration of cavitation shows that the frequency band of cavatation vibration is wide, 2000-10000Hz, when bubble collapse, it means the size of bubble is variable. Additionally, there exists concentrated bubble diameter at the frequency from 5400 to 6800Hz. Vibration frequency of the more concentrated impact on the coal seam gas desorption flow is more significant.④The experiments show that cavitation can effectively promote the methane desorption and seepage. Compared with the situation of no cavitation, desorption time of coal gas shortens by 16.4% and desorption quantity increases by 22.6% when cavitation number is 0.0038.⑤Adsorption barrier is decided by macromolecular structure of coal and components of gas, the deeper adsorption barrier is, the more energy is needed when desorption, and absorption mount is larger. The energy of desorption is provided by collisions of gas molecules or temperature rising. And it must be larger than wasted energy when absorption if methane molecules escapes from coal. The mechanism of gas desorption and seepage under sonic vibrating of cavitation water jets through the effects of mechanical vibration, thermal effects and the effects of hydraulic fracturing and damage to the promotion of coal seam gas desorption and seepage is studied theoretically. Imposed cavitation sonic vibrating, mechanical vibration effects reduce the coal skeleton stress, fracturing damage effect to improve the porosity of coal, coal bed system temperature for the coal seam gas desorption, together strengthen desorption and seepage of coal seam gas.⑥Field tests show that using high pressure water jet cutting drilling and cavitation sonic vibrating, the highest single hole concentration of gas extraction increased by 27.3 times, the highest pure gas drainage rate by 15 times. Under the same conditions with the occurrence of coal projects crosscut than expected time to reduce 45.27%. Reduce the number of pre-drilling holes 30.5%, 33.7% reduction of drilling footage.Three Main innovation points of the dissertation are:①The first time a high-pressure water jet cavitation visualization experiment of the entire process to determine the pump pressure, confining pressure on the cavitation effects, reveal the mechanism of bubble cloud breeding, development, and collapse and shaped features, is carried out.②Sonic vibrating of cavitation water jet is firstly moved to promote methane desorption, seepage and methane drainage rate, using self-developed cavitation sonic vibrating for coal gas desorption flow experimental equipment, and the relationship model between cavitation water jet parameters and coal gas desorption flow is set up.③The cavitation noise spectrum optimization model, attenuation law, noise wave energy equation and model of mechanical vibration induced crack damage is established, and the mechanism of sonic vibrating of cavitation water jet to promote methane desorption and seepage is revealed. It is the fundamental basic of theory and experiment for its engineering application.更多还原