煤岩体水力压裂裂缝扩展及对瓦斯运移影响研究

发布时间：2018-03-06 01:30

本文选题：煤岩体　切入点：水力压裂　出处：《重庆大学》2014年博士论文　论文类型：学位论文

【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。
[Abstract]:With the increase of mining depth, increasing the risk of coal and gas outburst. With coal outburst danger for low permeability and how to reduce the risk of coal and gas outburst is a major security technology problem to be solved. The hydraulic fracturing of coal rock is the extraction of coal gas in low permeability, effective method of outburst coal the body of outburst, especially for single low permeability outburst coal. Expansion and gas migration in coal and rock mass hydraulic fracture is a major factor in determining the effect of hydraulic fracturing of coal and rock. Therefore, the extension of hydraulic fracture of coal and rock and gas migration as the main research object, using theoretical analysis, system method, numerical calculation and field test the combination of the in-depth study of the coal rock mass hydraulic fracturing crack propagation and the influence on gas migration. The main research results and conclusions:
Firstly, the coupled mathematical model of hydraulic fracturing of coal rock mass seepage damage, non uniformity of the model adopts the statistical method to characterize the coal rock mass parameters, involving the coupling effect of seepage field and stress field, including elastic brittle, elastic softening and weakening of 3 kinds of elastic damage constitutive, considering the damage evolution process and the effect on the permeability of the physical parameters; the coupling iterative algorithm of the mathematical model, and finite element programming numerical solution by using Matlab software. By comparing the results and analytical solution with commercial software, verifies the correctness of the mathematical model and numerical solution; non uniformity of coal rock mass, initial stress and hole of hydraulic fracturing, the influence of expansion, pre fracturing and hydraulic slotting guide porous control fracturing fracture water control The mechanism and influencing factors are used to provide theoretical basis for the design of field hydraulic fracturing parameters and the control of fracturing.
The methane driven hydraulic fracturing effect, change the gas flow and effect of gas adsorption and desorption characteristics of the three aspects of the influence of coal rock mass hydraulic fracturing of gas migration is proposed. The coal rock mass hydraulic fracturing and gas drainage unified mathematical model, numerical simulation of gas production after fracturing and applied to the study of gas migration law after fracturing; the numerical results show that the coal gas pressure damage unit was significantly reduced, indicating the coal pressure crack permeability is improved, the formation of a new "broad channel of gas migration smoothly, significantly improves the gas drainage effect. The results of drainage borehole layout optimization has guiding significance on the field of fracturing drilling and gas.
Based on the coal rock deformation model, hydraulic fracture plane pressure drop model and hydraulic crack propagation model was established for low permeability coal rock hydraulic fracturing single crack propagation mathematical model, put forward the numerical algorithm of the mathematical model, and use APDL two development language is employed. To determine the injection pressure, coal and rock influence of elastic modulus, initial stress field and the viscosity of fracturing fluid for hydraulic fracturing of single crack propagation. The results for the hydraulic fracturing operation parameters provide theoretical guidance.
The coal injection to 6 degree discriminant index based on construction of the coal rock mass hydraulic fracturing after injection of the degree of difficulty of Fisher discriminant model and extension discriminant model. Results the engineering example shows that the results of 2 methods and engineering classification, fuzzy clustering method and neural network method is consistent with the result or better and realized after fracturing coal injection to the scientific evaluation of degree and classification, provides a reference to determine the feasibility of hydraulic fracturing after taking further measures the static pressure water injection.
The propagation of hydraulic fractures based on the theory and Research on the effects of the gas migration, taking into account the factors considered in coal mine construction conditions and gas drainage, put forward the coal rock mass hydraulic fracturing technology, the technology of coal rock mass permeability, gas drive, drainage and water injection in one wet coal rock mass hydraulic fracturing site. Tests show that the expansion of hydraulic fracture through the process of closed - Open - new cracks ", with the increase of hydraulic fracturing hole and crack front distance, water pressure attenuation, hydraulic crack propagation required water pressure increases; increasing gas concentration after fracturing and fracturing borehole drilling investigation and verification the effect of methane driven fracturing. Mining and outburst prediction index results show that pumping site gas drainage and mining, concentration of pure quantity showed a" high low high "special gas fracturing drilling Point; outburst prediction of fracturing effect within the scope of the index did not exceed the standard, the influence of gas migration in coal rock hydraulic fracturing theory test, permeability that hydraulic fracturing technology can effectively increase the coal mass and improve the gas drainage rate and eliminate the danger of coal and gas outburst, and has remarkable technical and economic benefits.

【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TD712

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