【作者】 李贤忠；

【导师】 林柏泉；

【作者基本信息】 中国矿业大学 ， 安全技术及工程， 2013， 博士

【摘要】 在我国煤矿开采过程中，与瓦斯相关的危害越来越严重，严重影响煤矿安全生产。同时瓦斯作为一种非常规天然气能源，储量达36.8万亿m3。我国70%左右的煤层瓦斯赋存具有微孔隙、低渗透率、高吸附的特征。水力压裂是提高煤层瓦斯抽采效率的有效技术措施之一，但是现有水力压裂技术需设备大、压力大，不利于煤矿井下推广。本文采用理论分析、实验研究和现场试验相结合的方法，在常规水力压裂基础上提出了脉动水力压裂技术，取得如下主要研究成果：首先研究了地应力和脉动压力波两种载荷作用下煤岩体破裂损伤机理。分析了脉动压力波产生机理，确定流量脉动率。在分析煤岩体孔隙、裂隙的基础上，研究地应力对煤岩体力学性质及对水力压裂的影响规律。确定总应力强度因子为地应力与脉动压力波分别作用于煤岩体上位移和应力的分量之和，描绘出总应力强度因子曲线。研究水力压裂起裂及扩展机理，并利用数值模拟软件验证，得出水力压裂能使煤岩体应力带想压裂孔两侧煤层深处移动，并在大范围内形成了塑性变形，有效降低地应力的同时破坏煤岩体，有效降低煤层的瓦斯压力。第二、将脉动压力的传播看做应力波的传播，选取瞬变流模型为研究脉动压力波传播基本模型，利用脉动压力传播方程对脉动压力进行数值计算，分析裂隙贯通前后脉动压强变化规律，脉动反射波由于波速和流速的叠加，使其在裂隙尖端出现压力增大的现象。利用脉动水力压裂平台验证在管路闭合条件下，脉动频率为50Hz与40Hz时，脉动压力波波峰在裂隙尖端出现压力增大现象，最大增幅50%。在此基础上研究脉动压力波破煤岩机理，得出脉动水力压裂能以较小的脉动压力取得常规水力压裂的效果。第三、针对本煤层脉动水力压裂封孔困难的状况，分析高压封孔的基本原理，通过添加膨胀剂、减水剂等材料研制出水泥基抗高压封孔材料，通过实验分别得出膨胀剂与减水剂的添加配比，利用低场核磁共振设备研究添加膨胀剂与减水剂的水泥浆体的水化反应过程，将水化反应分为四个阶段，指出在反应期（1.5h之内）完成现场注浆工作，得出水化反应的起始时间，为现场施工提供理论指导。最后，为配合高压脉动水力压裂技术的应用，解决工程实践中遇到的问题，研制了高压脉动水力压裂一体化装备，提出治理高瓦斯低透气性煤层卸压增透的“钻”“压”“抽”三位一体技术，并在此基础上将该装备应用于晋煤集团成庄矿，共在三个不同区域进行试验，对相关参数进行了测定分析。研究成果在现场应用表明，实施脉动水力压裂后，瓦斯抽采效果明显。脉压裂孔平均纯流量为0.05m3/min，为普通抽采孔的2.5倍。压裂结束后压裂区域含水量提高2倍左右，煤层透气性系数增加了47.8倍，达到41m2/(MPa2d)，压裂后压裂孔周围10m范围内脉冲及辐值明显降低，使支承压力峰值降低。研究结果对于单一低透煤层瓦斯防治提供理论与实践基础，课题研究期间作者发表学术论文7篇，其中EI检索两篇，EI录用两篇，获得各项科研奖励5项。更多还原

【Abstract】 During the process of coal mining in China, the hazards related to gas is moreand more serious, which will not only affect the coal mine production safety, but gasemissions into the air will also cause atmospheric pollution, meanwhile gas as a kindof unconventional natural gas energy, reserves of36.8trillion m3. About70%ofChina Coalbed gas have the characteristics of micro-porosity, low permeability andhigh adsorption, resulting the gas disaster-prone. Hydraulic fracturing is an effectivetechnique to improve the efficiency of gas extraction from coal seam, but the existinghydraulic fracturing technology has big equipment and pressure, which is notconducive to the coal mine.We developed pulsating hydraulic fracturing technologybased on the conventional hydraulic fracturing, which can increase seam permeability,reduce stress and increase the amount of gas drainage.In this paper, we analysed the fracture damage mechanism of coal rock massunder the effect of two loads, crustal stress and pulsating stress wave firstly,confirmed that the total stress intensity should be the sum of displacement and stresscomponent of crustal stress and pulsating stress wave acting on the coal rock mass.Total stress intensity factor curve was traced out and pulsating hydraulic fracturingprocess can be divided into three stages. Under repetitive effect of pulsating stresswave, the energy of coal rock mass accumulates continuously which makes it fracturerandomly. The fracture of coal rock mass makes the static stress field changescontinuously, meanwhile, the follow-up dynamic stress field changes randomly.Comprehensive changes of the two stress fields increases the randomness of fatiguedamage of rock mass in turn and then lead to the damage accumulates continuously,mechanical property of rock mass degenerates ceaseless, at last, it makes thecondition of jointed rock changes from crack initiation, expansion to joint wellconnected. Analysis of numerical simulation showed that after hydraulic fracturing,crustal stress of elevated stress area on both sides of cracks reduced to a very lowlevel and plastic deformation was formed in a large area. This indicates that hydraulicfracturing technology can reduce the crustal stress effectively while damaging coalrock mass and reduce the gas pressure of coal seam. At the same time, direction ofcoal crack can be controlled by setting oriented control drill holes.secondly, regarding the spread of pulsating pressure as the propagation of stresswave, the transient flow model was selected for the study of pulse pressure wave propagation, fluctuating pressure propagation equation was used to calculate the valueof fluctuating pressure. The variation of fluctuating pressure before and after thecracks connect with each other was analysed. Due to the superposition of wavevelocity and flow velocity, pressure of pulsating reflected wave increases at the tip ofcrack. Using pulsating hydraulic fracturing experiment platform, different pulsefrequency was tested. At the condition of50Hz, pulsating stress wave increased by50%, reached to1.5MPa. However, at40Hz, pulsating stress wave increased by28.6%, reached to0.9MPa. It can be seen that the damage effect on coal-rock mass isbetter at the condition of50Hz.Thirdly, we analyzed the basic principle of the high pressure sealing in responseto the problems of drilling sealing in pulsating hydraulic fracturing. We determinedthe ratio of expansion agent and water reducing agent through experiments, anddeveloped the cement-based high-pressure sealing material by adding expansion agentand water reducing agent. What’s more, the hydration process of cement paste withexpansion agent and water reducing agent was divided into four stages, through theresearch by low-field NMR equipment in it. It was pointed out that the grouting workshould accomplished during the reaction period and the start time of hydration processwas33~35minutes, providing theoretical guidance for the site construction.Finally, to cope with the application of high pressure pulse hydraulic fracturingtechnology and problems occurred in engineering practice, we manufactured theintegration equipment of high pressure pulsating hydraulic fracturing, proposed drill-fracture-drainage trinity technology for pressure relief and permeability increase inhigh gas, low permeability coal seam. On that basis, the equipment was applied in theChengzhuang Mine of Jinmei Group. Field tests were conducted in three differentareas and relevant parameters were analysed.Field test results show that there is an obvious effect in gas extraction afterpulsating hydraulic fracturing. The average pure flow of pulsation fracturing hole is0.05m3/min,2.5times of normal drainage hole. After fracturing, water content infracturing area increased by2times and permeability coefficient of coal seamincreased by47.8times, reached to41m2/(MPa2d). Pulse and amplitude valuedecreased obviously within the10m range of fracturing hole which reduces the peakvalue of abutment pressure.In addition,7papers about research results were and will be published, in which2has been indexed by EI,2will be published in EI source journals.更多还原