井下水力压裂煤层应力场与瓦斯流场模拟研究

发布时间：2018-06-22 04:42

本文选题：井下水力压裂 + 应力场　；参考：《中国矿业大学》2013年博士论文

【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。
[Abstract]:Aiming at the negative effect of the increase of coal body moisture on gas migration and the redistribution of gas field, seepage field and stress field in the process of hydraulic fracturing in underground coal seam, theoretical analysis and numerical simulation are used in this paper. Combining the laboratory experiment with the field industrial test, the underground hydraulic fracturing technology with different coal structure adaptability is analyzed, and the gas desorption law under the condition of coal-water-gas three-phase medium is studied. The distribution characteristics of in-situ stress in the area affected by hydraulic fracturing are revealed, and the dual effect of gas migration and production in hydraulic fracturing coal seam is discussed. The feasibility of using transient electromagnetic method and tracer method to study and evaluate the distribution characteristics of hydraulic fracturing flow field in underground coal seam is pointed out. (1) the experimental and experimental study on the law of gas desorption under the condition of coal-water-gas three-phase medium shows that; The higher the moisture content of coal sample is, the less the cumulative desorption amount is, and the lower the gas desorption rate is; The results show that water can not only restrain the gas desorption migration, but also reveal the check index of the gas desorption and migration under the condition of water content, and cover up the danger of coal and gas outburst. (2) the numerical simulation of hydraulic fracturing in single hole shows that The in-situ stress on both sides of the fracturing hole has been greatly reduced, the in-situ stress has been reduced to a low body in a wide range, the displacement occurred on both sides of the borehole and the Z direction coal body, and the variation characteristics of the cuttings amount in the affected area of hydraulic fracturing, The results show that the stress distribution state of the coal face after fracturing is the same as the numerical simulation results of stress field characteristics in the area affected by fracturing, where the length of pressure relief zone increases and the response of cuttings quantity changes after fracturing. At the same time, the shortage of hydraulic fracturing is found by numerical simulation, and a new stress concentration is also produced at the fracture tip. (3) aiming at the complexity and heterogeneity of the geological conditions of coal seam occurrence, As well as the phenomena such as short circuit of fracturing fluid flow field, uneven distribution of fracture propagation, stress concentration at the tip of single hole and so on in the process of hydraulic fracturing, it is proposed that "double hole (porous) uniform fracturing, directional drilling control fracturing, hydraulic jet assisted fracturing, etc." In advance hydraulic fracturing and directional fracturing with wedge ring groove "5 kinds of fracturing are used to realize the whole of coal seam." Optimization technology of uniform fracturing. (4) by using Reynolds number and starting pressure gradient 位, the positive effect of hydraulic fracturing on accelerating gas production and the negative effect of increasing coal moisture on gas migration are studied. Water cut is not the main factor affecting the starting pressure gradient. When the permeability of coal bed increases to a certain extent, the starting pressure gradient will disappear. The effect of water increase on gas drainage is limited. The essence of hydraulic fracturing and accelerating gas drainage is to change the gas flow state in coal seam, compared with the negative effect caused by fracturing fluid filtration during fracturing. The positive effect of anti-permeability fracturing plays a controlling role in gas migration and production. (5) in order to evaluate the distribution characteristics of fracturing flow field (seepage ability, influence range, uniformity), The mathematical model of flow field evaluation for gas-bearing coal body hydraulic fracturing is established, and the theory and experimental research on the distribution characteristics of hydraulic fracturing flow field based on transient electromagnetic method and tracer tracking method are carried out, which enriches the methods and means of underground hydraulic fracturing evaluation. It has great application value to improve the construction quality and reduce the construction risk.
【学位授予单位】：中国矿业大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TD825;TD712

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