基于电破碎效应的脉冲致裂煤体增渗实验研究

发布时间：2018-05-25 00:18

本文选题：电破碎效应 + 煤体　；参考：《中国矿业大学》2017年博士论文

【摘要】：我国煤层气资源储量丰富,但由于煤层渗透率低,使大部分煤矿瓦斯抽采效率受到了严重制约。采取适当的技术手段、人为地增加煤层透气性是提高瓦斯抽采效率的重要途径。为此,本文针对基于电破碎效应的脉冲致裂煤体增渗方法开展了实验研究,以期为煤层气高效开发探索一条新的途径。搭建了煤岩电脉冲致裂增渗实验系统,以焦作无烟煤、淮北无烟煤、陕西烟煤、甘肃烟煤和内蒙古烟煤等5种煤样为研究对象,在空气环境下对5种煤样进行了电脉冲击穿致裂增渗实验。并以淮北无烟煤和甘肃烟煤为例研究了煤样尺寸、含水率和击穿电压等因素对电脉冲致裂煤体的影响。利用扫描电镜、红外光谱分析、压汞法和低温液氮吸附法分析了电脉冲技术对煤体微观结构的影响。同时,搭建了渗流实验系统,以淮北无烟煤为例定量研究了受围压约束的煤体在电脉冲击穿致裂后渗透率的改善效果。在实验研究的基础上,探讨了高压电脉冲致裂煤体的增渗机理。最后提出了电脉冲技术在低透气性煤层增透方面的潜在应用方法。主要研究成果如下:(1)明确了煤样在空气环境下电脉冲击穿的基本形式。研究表明:在空气环境下,煤样的电脉冲击穿有内部击穿和沿面击穿2种形式。内部击穿是电脉冲击穿过程中的等离子体通道从煤样内部通过,巨大的能量在瞬间注入等离子体通道内,形成的高温热膨胀力和冲击波使煤样发生破碎,煤样表面均呈现出烧灼状态,原生结构被破坏,形成了很多孔隙和裂隙。沿面击穿是等离子体通道沿着煤样表面发展,最终与两个电极连通,发生沿面击穿时等离子体通道中的能量大部分耗散于空气中,导致煤样没有发生明显的破坏。(2)发现了煤体内部击穿电压和击穿场强的变化规律。研究发现:在煤样长度不变的情况下,煤体发生内部击穿的概率随着煤样直径的增加呈现出上升趋势,但是煤样直径的变化对发生内部击穿时的击穿电压影响不明显;煤样的内部击穿电压随着含水率的增加呈下降趋势,随着煤样长度的增加而呈上升趋势;煤样的内部击穿场强与煤样的长度呈负指数关系,即:E(28)aeb L(10)c,式中,E为煤体的击穿场强,L为煤体长度,a,b(b(27)0)和c为常数。(3)揭示了煤样击穿后的孔隙结构演化特征。研究表明:随着击穿电压的增加,煤体表面的裂隙数量明显增加;电脉冲击穿后的煤体内部开放性的透气性孔有了一定程度的增加,煤体的微观孔隙结构有了较好的改善,但是微观孔隙结构的改善效果并不是击穿电压越大越好,随着击穿电压的上升,累积孔容呈现出先增加后减小的趋势,这意味着击穿电压存在一个最优值,当采用最佳的击穿电压时,可以使煤体内的孔容增加量达到最大值。(4)初步揭示了电脉冲击穿煤体的致裂增透机理。研究发现:在恒定的围压和不同的瓦斯压力下,被电脉冲击穿的煤样的渗透率比原煤的渗透率都有明显的增加,达到了原煤渗透率的1.4-2.2倍;在恒定的瓦斯压力和不同的围压下,电脉冲击穿煤体的渗透率也明显高于原煤的渗透率;基于固体电介质击穿理论、煤岩爆破损伤理论和煤层瓦斯渗流理论,探讨了电脉冲击穿煤体的致裂增渗机理,电脉冲击穿煤体的过程中,等离子体通道内形成的应力波作用于煤体,使煤体中形成了大量的连通裂隙,有效的提高了煤体的渗透率。(5)提出了电脉冲技术在煤层增透方面应用的三种技术设想:煤矿井下电脉冲击穿致裂煤体增渗技术、地面煤层气井电脉冲击穿煤体致裂增渗方法和地面煤层气井电脉冲解堵增渗方法。研究成果有助于完善高压电脉冲技术致裂煤体的增渗机理,为高压电脉冲技术在改善煤层渗透率的现场应用中提供理论支撑。课题研究期间发表论文8篇,其中SCI检索4篇,EI检索2篇,授权国家发明专利12项。
[Abstract]:China's coal seam gas reserves are abundant, but because of low coal seam permeability, most coal mine gas extraction efficiency has been severely restricted. Taking appropriate technical means to artificially increase the permeability of coal seam is an important way to improve gas extraction efficiency. An experimental study is carried out to explore a new way for the efficient development of coal bed gas. An experimental system of coal and rock electrical pulse fracturing is set up. 5 kinds of coal samples, such as Jiaozuo anthracite, Huaibei anthracite, Shaanxi bituminous coal, Gansu bituminous coal and Inner Mongolia bituminous coal, are used as the research objects, and 5 kinds of coal samples are subjected to electric pulse impact penetration enhancement under the air environment. Taking Huaibei anthracite and Gansu bituminous coal as an example, the influence of coal sample size, water content and breakdown voltage on electric pulse cracking coal body was studied. The influence of electric pulse technology on coal microstructure was analyzed by scanning electron microscope, infrared spectrum analysis, mercury injection method and low temperature liquid nitrogen adsorption method. At the same time, the seepage experiment system was built. In the case of Huaibei anthracite as an example, the effect of permeability improvement on the coal body subjected to the impact of the electric pulse is quantitatively studied. On the basis of the experimental study, the infiltration mechanism of the high pressure electric pulse cracking coal body is discussed. Finally, the potential application method of the electric pulse technology in the low permeability coal seam is put forward. The following are as follows: (1) the basic form of electric pulse impacting on coal samples in air environment is clarified. The study shows that in the air environment, the electric pulse of coal samples has 2 forms of internal breakdown and surface breakdown. The internal breakdown is the passage of the plasma channel from the inner part of the coal sample, and the huge energy is injected into the plasma in a moment. The high temperature thermal expansion force and shock wave formed in the road caused the coal sample to break up, the surface of the coal samples showed a burning state, the primary structure was destroyed and a lot of pores and cracks were formed. The surface breakdown along the surface is the plasma channel along the surface of the coal, and finally connected with the two electrodes, and the energy in the plasma channel is big when the surface is broken down. Partially dissipated in the air, the coal sample has not been destroyed obviously. (2) the change law of the breakdown voltage and the breakdown field strength of the coal body was found. The study found that the probability of internal breakdown of coal body appears to rise with the increase of coal sample diameter when the coal sample length is constant, but the change of coal sample diameter is occurring The internal breakdown voltage of internal breakdown is not obvious; the internal breakdown voltage of coal sample decreases with the increase of water content, and increases with the increase of coal sample length; the internal breakdown strength of coal samples is negatively exponential with the length of coal samples, that is, E (28) AEB L (10) C, E is the breakdown field strength of coal body, L is the length of coal, a, B (b). 27) 0) and C as a constant. (3) the pore structure evolution characteristics of coal sample after breakdown are revealed. The study shows that with the increase of breakdown voltage, the number of cracks on the surface of coal increases obviously; the opening of the coal body inside the coal body after the pulse is increased to a certain extent, and the micro pore structure of the coal body has been better improved, but the micro pore structure is slightly improved. The improvement effect of the pore structure is not the greater the breakdown voltage, the better the higher the breakdown voltage. With the rise of the breakdown voltage, the cumulative Kong Rong appears to increase first and then decrease, which means that the breakdown voltage has an optimal value. When the best breakdown voltage is used, the increase of the pore volume in the coal can reach the maximum. (4) the electric pulse is preliminarily revealed. It is found that under constant confining pressure and different gas pressure, the permeability of coal samples impacted by electric pulse increases significantly than the original coal permeability, reaching 1.4-2.2 times of the original coal permeability, and the permeability of the coal body under constant gas pressure and different confining pressure. It is obviously higher than the permeability of the raw coal; based on the theory of solid dielectric breakdown, the theory of coal rock blasting damage and the theory of coal seam gas seepage, the mechanism of the crack growth of the coal body is discussed. In the process of the electric pulse impacting the coal body, the stress wave formed in the plasma channel is used in the coal body, making a large number of connection cracks in the coal body. The porosity can effectively improve the permeability of coal. (5) three kinds of technical ideas for the application of electric pulse technology to coal seams are put forward: coal mine underground electric pulse impact penetrating coal infiltration technology, ground seam gas well electric pulse impacting coal body cracking increase method and surface coalbed gas well electric pulse plugging removal method. The osmotic mechanism of the cracked coal by the high pressure electric pulse technology provides the theoretical support for the field application of the high pressure electric pulse technology in improving the permeability of the coal seam. During the study period, 8 papers were published, of which 4 articles were retrieved by SCI, 2 articles were retrieved by EI, and 12 patents were authorized by the state.
【学位授予单位】：中国矿业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TD712.6

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