含瓦斯原煤宏-细-微三观结构动力水侵特征及瓦斯运移规律实验研究

Reveal dynamic water invasion characteristics of raw coal containing gas and its effect on gas migration, in order to provide theoretical basis for hydraulic control technique which is used to solve the gas disaster of deep mining in China's coal mine. Mechanical parameters of Water-pneumatic, fracture spread, water distribution and gas seepage characteristic in the Macro - Micro structure of water invasion coal containing gas was obtained by raw coal water dynamic injection experiment, the true triaxial shear flow experiment and observation of water invasion sample by SEM with computer image analysis, the fractal dimension of macro-meso structure and water dynamic injection infiltration fractal model of raw coal was obtained. Based on the test principle of pore structure by Nuclear Magnetic Resonance (NMR), the relationship of injection pressure, water content distribution and meso-micro pore structure was obtained by the test of water content in full scale pore structure, and the water dynamic injection permeability fractal model of raw coal containing gas was set up, combined with desorption experiment of water invasion coal containing gas, the influence of water invasion critical dimensions and water content distribution on gas desorption characteristics was obtained. By the radial seepage experiment combined with the permeability of effective stress expression, the relationship of adsorption-swelling stress of water invasion coal containing gas, adsorption parameters, mechanical parameters and the permeability of coal was obtained, the coupling model between micro-adsorption swelling of water invasion raw coal containing gas and macro seepage was establish. From macro-meso-micro scale, we reveal dynamic water invasion characteristics of raw coal containing gas and its effect mechanism on gas migration.

揭示含瓦斯原煤动力水侵特征及其对瓦斯运移规律的影响，将为我国高瓦斯矿井深部开采水力化防治技术提供理论基础。本项目通过原煤动力水侵、真三轴剪切渗流试验和水侵试样切片扫描电镜观测及计算机图像处理分析，获得宏-细观结构动力水侵过程中水气力学参数、裂隙展布、外侵水分布及承压水中瓦斯渗流特征，优选表征原煤宏-细观结构分形维数，构建宏-细观结构水侵渗透率分形模型；基于NMR测试孔隙结构原理，结合全尺度孔隙水含量分布试验，获得原煤微-细观孔隙结构水侵压力、水含量与孔隙结构间量化关系，构建微-细观结构水侵渗透率分形模型，结合解吸试验，获得水侵临界尺度、水含量分布对瓦斯解吸特性影响；通过径向渗流试验，结合渗透率有效应力表达式，建立水侵含瓦斯原煤吸附膨胀应力、吸附参数、煤体力学参数与渗透率间关系，构建水侵原煤瓦斯微观吸附膨胀与宏观渗流耦合模型；从宏-细-微三观尺度揭示含瓦斯原煤动力水侵特征及其对瓦斯运移影响。

含瓦斯原煤动力水侵过程是一个气-液-固三相体系相互作用的复杂力学过程，揭示动力水侵特征及其对瓦斯运移规律的影响，对提升我国矿井瓦斯防治技术水平具有重要理论意义。本项目首先采用多种实验手段，结合分形理论研究了水侵煤体全尺度结构分布及分形特征，并通过不同水侵方式含瓦斯原煤核磁共振测试，从宏-细观角度分析了注水煤层真实力学环境下原煤孔隙结构与水侵压力间量化关系以及水侵煤体渗透特性；其后，基于自研原煤高压水侵及径向气体渗流实验系统开展了不同覆压、瓦斯压力下原煤水侵驱气实验，提出了一种考虑毛细管力的有效应力模型，揭示了动力水侵过程中煤-水-气力学作用机制；最后开展了水侵含瓦斯煤样的径向稳态渗流实验，结合渗透率有效应力模型，定量分析了水侵原煤瓦斯吸附膨胀与渗流耦合特性。研究表明：水侵过程中水压和围压主要改变中孔与大孔结构，高压水的扩孔作用可有效沟通孔隙网络，增加孔体积，而增大围压会压缩煤体，减小孔体积；结合水侵原煤宏-细观结构渗透率分形模型对比发现，在宏-细观尺度内理论与实测渗透率的变化规律一致；同时，在动力水侵初始阶段，水在低渗煤层内流动存在启动压力梯度，符合非线性渗流特征，随覆压增加，煤层渗透率明显降低，启动压力梯度显著增大，根据实验结果及启动压力梯度与渗透率间的幂指数函数关系，获得了含瓦斯煤层注水非线性渗流特性；瓦斯径向稳态渗流实验表明，煤吸附CH4与水均导致煤体膨胀变形进而降低渗透率，随渗流压力增加，CH4在干燥煤样中的渗透率降低，He气在干燥煤样中的渗透率恒定，随含水率增加，He气在湿煤样中的渗透率降低，呈指数函数关系；结合渗透率有效应力模型发现模型预测与实验测量值均表明煤吸附水膨胀变形高于煤吸附瓦斯的膨胀变形，阐明了水侵原煤瓦斯吸附膨胀与宏观渗流耦合关系。因此本课题全面系统阐明了含瓦斯原煤动力水侵及瓦斯运移这一复杂动力学过程，为我国深部开采水力化防治瓦斯技术应用和推广提供了理论支撑。