松软煤层瓦斯抽采钻孔失稳机理与控制技术基础研究

In view of horizontal gas extraction borehole instability and the influence of hole collapse on the gas extraction efficiency in soft seam, an instability experimental model and platform of the horizontal gas extraction borehole for soft coal seam will be established in the research. Through the methods of model testing, field monitoring, and theoretical analysis, firstly, creep properties of horizontal gas extraction borehole under the action of gas-solid coupling function will be conducted to reveal mechanism of borehole instability. A buckling failure criterion of borehole based on the risk assessment model will be proposed. Secondly, physical property changes of coal-rock mass and gas transportation rules around borehole under the coupling effect of creep and seepage will be researched, then effect evaluation index of gas extraction efficiency introducing time will be put forward. Finally, fundamental research of new borehole-protecting solutions based on borehole-protecting materials (hole-protecting sieve tube, high hardness porous nano-synthetic hole collapse prevention material, and high permeability gel composite material) and stationary protecting technology will be introduced and investigated for technical solution for effectively improving the gas drainage efficiency. Modeling test and field industrial test are expected to be used for revealing both dynamic changes of gas drainage efficiency and gas seepage characteristics around borehole before and after using different borehole-protected solutions. The proposed studies will further improve the existing theory, provide essential theory and practical solutions for high-efficient gas drainage in soft coal seam, and has important significance in operation for further increasing of the gas drainage efficiency and realizing high-efficient exploitation of coal and gas.

针对松软煤层水平瓦斯抽采钻孔失稳塌孔影响抽采效率的问题，基于地质力学模型试验技术，构建松软煤层水平瓦斯抽采钻孔失稳微缩模型实验平台；结合系列模型实验、现场监测和理论分析，研究气固耦合作用下水平瓦斯抽采钻孔蠕变失稳特征，建立基于风险评价模型的钻孔失稳破坏判定准则；研究蠕变-渗流耦合作用下钻孔周围煤层物性变化及瓦斯运移随时间的演化规律，建立引入时间变量的瓦斯抽采效果评价指标；同时开展护孔筛管、高硬度多孔纳米合成防塌孔护孔材料、高渗流胶凝复合护孔材料、“定点式”护孔技术的基础研究，分析护孔前后瓦斯抽采效率动态变化特性，以及钻孔周围煤层瓦斯运移规律。本研究将进一步完善瓦斯抽采钻孔失稳理论，提高瓦斯抽采效率，对实现煤与瓦斯安全共采具有重要的现实意义和实用价值。

长期以来，受松软煤层渗透率低和钻孔稳定性差等因素的影响，松软高瓦斯煤层瓦斯治理难度大，成为我国煤矿重大灾害的高发区域。基于此，本研究首先通过理论分析研究了水平钻孔周围岩体受力状态，推导了钻孔周围岩体弹塑性应力及钻孔围岩弹性位移公式，采用摩尔-库伦强度准则分析了不同侧压系数下钻孔壁失稳条件。其次，研究了瓦斯在煤体中的赋存状态、吸附理论及流动规律，分析了煤对瓦斯吸附及瓦斯在煤体中流动的主要影响因素。最后，通过实验室实验对PVC、PP、ABS三种管材打孔前后进行抗压性能研究，运用FLAC3D软件对三种筛管抗压性能进行数值模拟研究，并在淮北海子矿进行护孔筛管对比试验，得出ABS筛管抗压性能及瓦斯抽采效果均优于PVC筛管，接近裸孔瓦斯抽采效果。基于EH4电导率成像设备，开发了一套井下顺层钻孔变形特征内部影像监测系统，对钻孔内部蠕变过程进行实时监测。对塌孔常发区域提出定点支护技术，并开发了一种泡沫混凝土材料，该材料的抗压强度为20.37 MPa，平均孔隙率约为40 %，满足现场应用要求。本项目研究成果为深入理解松软煤层瓦斯抽放水平钻孔的失稳机制提供了基础，为高效支护钻孔提供了技术指导，对提高矿井瓦斯抽放效率具有重要研究价值。