【作者】 付江伟；

【导师】 傅雪海；

【作者基本信息】 中国矿业大学 ， 地质资源与地质工程， 2013， 博士

【摘要】 论文针对井下煤层水力压裂过程中滤失率引起的煤体水分增加对瓦斯运移的负效应以及“瓦斯场、渗流场、应力场”重新分布规律问题，采用理论分析、数值模拟、实验室实验和现场工业性试验相结合的方法，分析了不同煤体结构适应性的井下水力压裂技术，研究了煤-水-气三相介质条件下瓦斯解吸规律，揭示了水力压裂影响区域地应力分布特征，探讨了水力压裂煤层瓦斯运移产出的双重效应，指出了利用瞬变电磁法和示踪剂法对井下煤层水力压裂流场分布特征研究和评价的可行性。（1）煤-水-气三相介质条件下瓦斯解吸规律的实验/试验研究表明，煤样含水率越高，累计解吸量越少、瓦斯解吸速率越低；ΔP、q、K13个指标值随煤体含水率的增大而减小。说明水分对瓦斯解吸运移不但有抑制作用，同时还揭示出含水状态下所测试的校检指标，掩盖了煤与瓦斯突出危险性。（2）井下单孔水力压裂数值模拟表明，压裂孔两侧本来的应力升高区域地应力大大降低，很大范围内地应力都降低到低状体，钻孔两侧及Z方向煤体发生位移；现场水力压裂影响区钻屑量的变化特征，反映了压裂后集中应力带向煤体深部转移，采掘工作面卸压带长度增大，钻屑量变化响应的工作面应力分布状态，与压裂影响区应力场特征数值模拟结果一致；通过数值模拟同时也发现了水力压裂的不足之处，在裂缝尖端也产生了新的应力集中。（3）针对煤层赋存地质条件的复杂性和非均质性，以及水力压裂研究过程中出现的压裂液流场短路、裂隙扩展分布不均、单孔尖端应力集中等现象，提出了“双孔（多孔）均匀压裂、定向钻进控制压裂、水力喷射辅助压裂、预先水力割缝导向压裂、开楔形环槽定向压裂”5种用于实现煤层整体、均匀压裂的优化工艺。（4）利用流态判识标准雷诺数Re和启动压力梯度λ，对水力压裂增透加速瓦斯产出的正效应，以及煤体水分增大抑制瓦斯运移负效应的研究表明，含水率并不是影响启动压力梯度的主要因素，当煤层渗透率增大到一定程度，启动压力梯度就将消失，揭示了对于透气性较好的高渗煤层，水分的增加对瓦斯抽采的影响是有限的，水力压裂增透加速瓦斯抽采的本质是改变了瓦斯在煤层内流态，与压裂过程中压裂液滤失引起的负效应相比，压裂增透产生的正效应对瓦斯运移产出起控制作用。（5）针对在评价压裂流场分布特征（渗流能力、影响范围、均匀程度）方面存在的难题，构建了含瓦斯煤体水力压裂流场评价数学模型，开展了基于瞬变电磁法和示踪剂跟踪法的水力压裂流场分布特征理论和实验研究，丰富了井下水力压裂评价的方法和手段，对提高现场施工质量、减小施工风险有很大应用价值。更多还原

【Abstract】 According to the underground coal seam hydraulic fracturing process of coal moisturefiltration rate caused by the increase of gas migration in the negative effects as well as theredistribution problem of gas field, seepage field, stress field. This paper analysed thehydraulic fracturing technology in different coal structure adaptability and researched thegas desorption laws under coal-water-air three-phase medium conditions to reveal theeffect of regional stress distribution characteristics of hydraulic fracturing by adoptingtheoretical analysis, numerical simulation as well as combining laboratory experiment andindustrial experiment. Discussed the double effects of hydraulic fracturing of coalbed gasmigration and production and pointed out the feasibility of using transient electromagneticmethod and tracer method to study and evaluate underground coal seam hydraulicfracturing field distribution characteristics.(1) Experimental study on the gas desorption law which is under the condition ofcoal-water-air three-phase medium shows that the higher the coal sample moisture contentis, the less the cumulative desorption quantity and the lower the desorption rate will be;values of ΔP、q、K1decrease with the increase of coal water content. It not only gives thatwater has inhibitory effect on methane desorption and migration, but also reveals thechecking indexes which are tested under the moisture-contained condition conceal the riskof coal and gas outburst.(2) Numerical simulation of single drill hydraulic fracturing showed both sides of thedrill reduced greatly. The stress was reduced to a low state in a wide range. Coal bodydisplaced beside the drilling and in the direction on of Z. The variation of drilling cuttingsvolume of field test reflected stress concentration belt transferred to the deep coal seam.Pressure relief belt length increased in front of mining working face. The variation ofdrilling cuttings volume of field test corresponded to the distribution of stress state in thenumerical simulation. The shortage of hydraulic fracturing was discovered duringnumerical simulation. Hydraulic fracturing causes a new stress concentration at the cracktip.(3) In view of the complexity of geological conditions of coal seam occurrence andheterogeneity, and in the study of hydraulic fracturing fluid break down agent flow fieldshort circuit, fracture propagation maldistribution, haplopore point stress concentrationphenomena, propose diplopore（multihole）uniformity fracturing, directional drilling dam fracturing, hydrojet assistance fracturing, beforehand waterpower slotting guidingfracturing, karat cambridge ring gutter orient fracturing five strain design to realize coalseam whole, even used to implement the coal fracturing optimization process.(4) Flow state was applied for recognizing standard Reynolds number Re and startingpressure gradient. The studies on positive effect of hydraulic fracture accelerating gasproduction by increasing permeability, as well as negative effect of increasing moisturerestraining gas migration, reflected that moisture content is not the dominant factoraffecting the starting pressure gradient, however, while permeability of coal seam increasesto certain extent, starting pressure gradient vanishes. When it comes to a high permeabilitycoal seam, increasing moisture has a limited impact on gas extraction, and hydraulicfracture accelerating gas production by increasing permeability in essence alters the flowstate of gas in coal seam. Compared to negative effect caused by fracturing fluid loss, thepositive effect resulting from fracturing controls gas production.(5) For the problem of evaluating the distribution’s characteristics of fracturing’s flowfield(including seepage capability, influence area and degree of uniformity),we build amathematical model to evaluate the fracturing’s folw field of the coal containing gas. Weconducted the survey that is the distribution’s characteristics of fracturing’s flow field bymeans of experiment and theory,which is based on TEM and tracer method. It enriches themethod of evaluating the fracturing downhole and makes great application value toimprove the quality of site construction and reduce the risk of construction.更多还原