含瓦斯软煤钻孔塌孔机制及多孔材料填充护孔特性

Soft coal seams containing high gas exist in over 53.3% of coal mines across China. Coal and gas outburst occurs in these coal seams most frequently. However, gas control is greatly difficult in such places. Currently, gas drainage using boreholes is the main gas control method. Unfortunately, this method has technical problems which include difficulty of drilling, easy deformation and collapse of boreholes. Thus, it is urgent to study the deformation and collapse mechanism of soft gassy coal considering the effects of high geostress and drilling disturbance. Based on stress and strain relationship of soft coal, this program will propose the failure criterion of soft gassy coal. The mechanical model of borehole stability will be established for the quantitative analysis of relation between borehole stability, drilling loads, gas seepage and geostress. Moreover, this program will present new method of retaining boreholes in which particles of porous material are conveyed to fill boreholes. The seepage characteristics and the mechanical response of granular materials in boreholes will be studied. The influence of porous filling on borehole stability will be determined. This program will reveal the time-space evolution law of borehole deformation in soft coal influenced by the coupling effect of gas seepage, geostress and supporting stress. The achievements of the program can provide scientific guidance for drilling engineering of gas drainage in mining areas that contain soft coal seams.

我国53.3%以上的煤矿赋存有松软高瓦斯煤层，是煤与瓦斯突出事故易发、频发的主要区域。松软煤层瓦斯治理非常困难，目前主要依靠井下钻孔抽采，但是软煤钻孔存在钻进难、易变形、易塌孔等技术难题，亟需研究解决高地应力作用和钻进扰动下含瓦斯软煤钻孔变形垮塌机制这一关键课题。本项目基于软煤的应力应变关系，提出含瓦斯软煤的破坏准则，建立钻进动载荷影响下钻孔坍塌失稳的力学模型，定量分析钻孔稳定性与钻进载荷、瓦斯渗流和地应力的关系，揭示钻进扰动下含瓦斯软煤钻孔塌孔机制。提出气力输送多孔材料颗粒填充钻孔的新护孔方法，分析颗粒材料孔内渗流特征和支撑孔壁的力学响应，研究多孔材料充填对钻孔稳定性的影响规律，揭示煤层瓦斯渗流、地应力和支护应力耦合作用下软煤钻孔形变的时空演化规律。研究成果可为我国松软煤层矿区瓦斯抽采钻进工程提供科学指导。

针对高地应力软煤钻进扰动下钻孔塌孔和成孔后钻孔稳定性问题，本研究本节分析了软煤钻进时钻头切削体与煤岩体之间的接触应力分布。实验分析了钻进动载荷作用下松软煤体的应力应变特性，开展了动载荷作用下软煤单轴、三轴压缩实验，得到了煤体塑性、屈服及失稳发生的条件参数；考虑了孔隙压力沿钻孔径向的非线性分布特征，结合有效应力原理以及围岩非线性孔隙压力分布特征，基于软煤破坏特征的广义Hoke-Brown强度准则作为软煤破坏判据，对钻孔弹性区和塑性区应力进行了理论推导，得到了钻进动载荷影响下钻孔坍塌失稳的力学模型，分析了地质强度指标GSI、软煤钻进动载荷扰动系数D、应力不均衡系数λ、原始瓦斯压力对煤层钻孔稳定性的影响，引用参数R/D对钻孔稳定性等级划分。结合案例计算结果表明，地质强度指标GSI和应力不均衡系数λ是影响钻孔稳定的关键因素。钻孔周围瓦斯压力梯度变化，对抽采钻孔的稳定性影响不应被忽略；实验研究了三轴应力下含瓦斯软煤分级加载蠕变变形特性，考虑到软煤在蠕变各个阶段的特征，并引入损伤变量对软煤的粘性系数进行修正，建立了软煤粘弹塑性非线性蠕变本构模型，并推导出该模型的三维蠕变本构方程。以该模型为基础，借助数值模拟的方法分析了裸孔、不同强度充填支护后钻孔的稳定性；搭建了多孔材料充填体压缩-渗流实验平台，实验测试了聚苯乙烯(EPS)泡沫、聚氨酯（PU）泡沫、聚丙烯（EPP）泡沫四种不同充填强度材料颗粒体的压缩应变-渗流特性，测试了四种材料不同粒径充填体、多粒径1:1体积比混合、不同材质组合颗粒充填体的抽采导流能力变化规律，分析了在钻孔变形应力加载条件下不同几何特征尺度、充填强度、加载量对充填体导流能力的影响，为实际工程技术应用提供最佳工艺参数。

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