【作者】 袁志刚；

【导师】 王宏图；

【作者基本信息】 重庆大学 ， 采矿工程， 2014， 博士

【摘要】 随着煤矿开采深度的增加，煤与瓦斯突出危险性不断增加。对于低渗透性且具有突出危险的煤体，如何有效降低煤与瓦斯突出危险性是亟待解决的重大安全科技问题。煤岩体水力压裂是低渗透煤体瓦斯抽采、突出煤体消突的有效技术途径，尤其是对于单一低渗突出煤体。煤岩体水压裂缝的扩展及瓦斯运移是决定煤岩体水力压裂效果的主要因素。为此，本文以煤岩体水压裂缝扩展及瓦斯运移为主要研究对象，采用理论分析、数值计算和现场试验相结合的方法，系统、深入地研究了煤岩体水力压裂裂缝扩展及对瓦斯运移影响。本文的主要研究成果与结论有：①建立了煤岩体水力压裂渗流—损伤耦合数学模型，该模型采用统计方法来表征煤岩体参数的非均匀性，涉及了渗流场和应力场的耦合作用，内含弹—脆性、弹性软化和弹性弱化3种损伤本构，考虑了损伤的演化过程及其对渗透率等物理参数的影响；提出了该数学模型的耦合迭代求解算法，并利用Matlab软件进行有限元编程实现了数值求解，通过与商业软件计算结果及理论解析解的比较，验证了该数学模型及其数值解法的正确性；系统研究了煤岩体的非均匀性、初始地应力场和钻孔孔径对水压裂缝起裂、扩展的影响，研究了预先水力割缝导向压裂法和多孔控制压裂法的水压裂缝控制机制及影响因素，研究结果为现场水力压裂参数设计及控制压裂提供了理论依据。②从水力压裂驱赶瓦斯效应、改变瓦斯流态和影响瓦斯吸附解吸特性三方面研究了煤岩体水力压裂对瓦斯运移的影响。提出了煤岩体水力压裂与瓦斯抽采统一数学模型，并应用于压裂后的瓦斯抽采数值模拟，研究压裂后的瓦斯运移规律；数值计算结果表明，损伤单元的煤体瓦斯压力降低明显，说明水压裂缝处的煤体透气性得到改善，形成了新的“更宽阔、通畅”的瓦斯运移通道，显著提高了瓦斯抽采效果。研究结果对现场压裂钻孔和瓦斯抽采钻孔布置优化具有指导意义。③基于煤岩体变形模型、水压裂缝面内流体压降模型和水压裂缝扩展模型，建立了低渗透煤岩体水力压裂单一裂缝扩展数学模型，提出了该数学模型的数值求解算法，并利用APDL二次开发语言实现了数值求解。确定了注入压力、煤岩体弹性模量、初始地应力场以及压裂液黏度对水力压裂单一裂缝扩展的影响规律。研究结果为现场水力压裂施工作业参数选择提供理论指导。④基于煤体注水难易程度的6个判别指标，构建了煤岩体水力压裂后注水难易程度的Fisher判别模型和可拓判别模型。工程实例判别结果表明，2种方法的判别结果与工程勘察分类、模糊聚类法和神经网络法的结果一致或更好，实现了压裂后煤体注水难易程度的科学评价和分类，为水力压裂后进一步采取静压注水措施的可行性判断提供了参考依据。⑤基于水力压裂裂缝扩展规律及其对瓦斯的运移影响理论研究，并兼顾考虑煤矿井下施工条件和瓦斯抽采等制约因素，提出了煤岩体水力压裂技术，该技术集煤岩体增透、瓦斯驱赶、抽采与注水湿润于一体。煤岩体水力压裂现场试验结果表明，水压裂缝的扩展经历了“闭合—张开—产生新裂缝”的过程，随着压裂孔与水压裂缝前沿距离的增大，水压力沿程衰减，水压裂缝扩展所需的水压不断增大；压裂后的考察钻孔和压裂钻孔中的瓦斯浓度增加，验证了水力压裂的驱赶瓦斯效应。现场瓦斯抽采和突出预测指标结果表明，压裂钻孔的瓦斯抽采浓度和抽采纯量呈现“高—低—高”的特点；压裂影响范围内的突出危险性预测指标值均未超标，验证了煤岩体水力压裂对瓦斯运移的影响理论，即水力压裂技术可有效增大煤岩体的透气性，提高瓦斯抽采率和消除煤与瓦斯突出危险性，并具有显著的技术经济效益。更多还原

【Abstract】 With the increase of mining depth, the risk of coal and gas outburst increases. Howto reduce coal and gas outburst risk effectively is a major safety problem and letter to beresolved for low permeability and gas bursting coal seam. Hydraulic fracturing ofcoal-rock mass is an effective technical approach for gas drainage of low permeabilityand gas bursting coal seam, especially for a single coal seam. Crack propagation ofhydraulic fracturing for coal-rock mass and gas migration are major factors deciding theeffect of hydraulic fracturing. Thus, this paper took crack propagation of hydraulicfracturing for coal-rock mass and gas migration as main study object, crack propagationof hydraulic fracturing for coal-rock mass and its influence on gas migration weresystematically and thoroughly studied by combining theoretical analysis with numericalsimulation and field investigation, which had important theoretical significance andengineering application prospect. The main research results and conclusions are asfollows:Firstly, mathematical model for seepage and damage coupling of hydraulicfracturing was established, which used statistical approach to represent heterogeneity ofcoal-rock mass parameters, involved coupling effect between seepage filed and stressfield, contained three constitutive relations, namely elastic-brittle, elastic-soften andelastic-weaken, considered the evolutionary process of damage and its influence onpermeability and other physical parameters; the coupling iterative algorithm for thismodel was worked out and numerically solved by finite element programming usingmatlab software, and the results of which were compared with business software andtheoretical analsysis, which verified the validity of mathematical model and itsnumerical method. Designed programme of numerical calculations were used to studyheterogeneity of coal-rock mass, in-situ stress field, diameter and shape of boreholewhose influences on crack and propagation of hydraulic fracturing for coal-rock mass.Hydraulic fracturing technology of hydraulic cutting in advance and multiboreholecontrol fracturing were studied. The above research results provided theoretical basisfor parameter design and borehole layout for field hydraulic fracturing.Secondly, gas migration influenced by hydraulic fracturing was studied from threeaspects, namely methane driven effect, gas flow feature changed and gas adsorption anddesorption influenced. Based on this, the unified mathematical model for hydraulic fracturing and gas drainage was established, and then was applied to numericalsimulation of gas drainage after fracturing, which studied the gas migration afterfracturing. The results proved that gas pressure near damage zone decreasedsignificantly, which illustrated that coal seam permeability near hydraulic fracture wasgreatly improved and new gas migration channel was formed near hydraulic fracture,which could significantly improve gas drainage effect. The above results providedguiding significance for the field borehole location optimization of gas drainage.Thirdly, based on deformation model of coal-rock mass, fluid pressure drop modelin hydraulic fracture, crack model and criterion for hydraulic fracture propagation,mathematical model of single crack propagation for low permeability coal-rock masswas established, whose numerical algorithm was studied and implemented using thesecondary development language APDL of ANSYS. The crack propagationcharacteristics, by changing injection pressure, elastic modulue, and in-situ stress fieldand fracturing fluid viscosity respectively were studied. The numerical simulationresults were consistent with the field observation results, which showed that thesimulation results could provide guidance for the choice of field construction parameterof hydraulic fracturing.Fourthly, based on six discriminant index of water infusion difficulty degree forcoal seam, Fisher discrimination model and extension discrimination model for coalseam water infusion difficulty degree after hydraulic fracturing were built. Thediscrimination results of engineering cases showed that the two above methods wereconsistent or better than the results of engineering investigation, fuzzy clusteringmethod and neural network method, which achieved the scientific evaluation andclassification of water infusion difficulty degree after hydraulic fracturing, and providedreference for the feasibility judgement of static pressure water infusion measure afterhydraulic fracturing to prevent coal and gas outburst.Fifthly, aiming at different coal structure types and considering constructionconditions underground coal mine and constraint factors of gas drainage, hydraulicfracturing process and technology was proposed, and then was applied in guiding thedesign of field hydraulic fracturing. The field hydraulic fracturing observation resultsshowed that the crack propagation had went through process of closure, expansion andnew crack generated. With the increase of distance between borehole and fractureleading edge, the water pressure decayed along distance and the intrinsic crack reopened,the water pressure needed for crack propagation was increased gradually. The gas concentration in inspection boreholes and fracturing boreholes after hydraulic fracturingwer all increased, which verified the methane driven effect of hydraulic fracturing. Thefiled investigation results of gas drainage and outburst prediction index showed that thegas drainage scalar quantity was high and kept smooth and steady during initial gasdrainage stage, followed by a short reduction period, and then gas drainage scalarquantity increased again later, a persistent gas production period emerged; besides, theoutburst prediction index in the influence range of hydraulic fracturing was lower thanthe critical index, which verified gas migration influenced by hydraulic fracturing,namely, hydraulic fracturing of coal-rock mass could increase permeability of coal-rockmass effectively, enhance gas drainage efficiency and eliminate the risk of coal and gasoutburst, it had obvious technical and economic benefit.更多还原