水分对低阶煤瓦斯时变扩散动力学影响机制及突出指标响应

The low rank coal accounts for more than 55% of the proved coal reserves in China. It has the characteristics of high natural moisture content. The change of moisture content significantly affects the gas desorption-diffusion characteristics and outburst indexes. The basic researches of effect of moisture on gas diffusion kinetics of low rank coal are insufficient. This project takes low rank coal with different natural moisture contents as the research object to study pore structure of water-containing coal with experiment methods of small angle X-ray scattering and low field nuclear magnetic resonance. This project uses quantum chemistry calculations combined with infrared spectroscopy to characterize the "water-methane-coal" molecular interactions. This project starts comparing experiments on expansion deformation of adsorbed water and methane by coal. We design a test method of gas desorption characteristics with water-containing coal to obtain the characteristics and key parameters of desorption curves of low rank coal with different water contents. We propose the mechanism of synergism of adsorption swelling and water-methane competitive adsorption with gas diffusion kinetics of low rank coal. Based on the full-time desorption and diffusion of coal particles and the pore-scale effect of water-induced matrix expansion, a time-varying diffusion coefficient was introduced to establish a low rank coal gas diffusion model, which reveals the mechanism of moisture on kinetics of gas full-time diffusion in low rank coal. We will grasp the response feature and rule of the outburst indexes on moisture to explain the internal relations between moisture and outburst indexes, which provides a theoretical basis for outburst prediction and prevention in low rank coal seams.

低阶煤占我国已探明煤炭储量55%以上，具有自然含水率高特点。水分变化显著影响瓦斯解吸扩散特性及突出指标，而水分对低阶煤瓦斯解吸扩散动力学影响机制研究尚存不足。本项目以不同自然含水率低阶煤为研究对象，采用小角X射线散射和低场核磁共振研究含水煤孔隙特征，运用量子化学计算结合红外光谱表征“水-甲烷-煤”分子相互作用；开展煤吸附水和甲烷膨胀变形对比实验，研发含水煤甲烷解吸特征测试方法，获得不同含水率低阶煤解吸曲线变化特征和关键参数，提出吸附水膨胀和水-甲烷竞争吸附对低阶煤甲烷解吸动力学协同作用机制；基于煤粒甲烷全时解吸扩散规律与水分诱导基质膨胀孔隙尺度改变作用，引入扩散系数时变效应，建立考虑水分影响的低阶煤甲烷扩散模型，揭示水分对低阶煤甲烷全时扩散动力学作用机制；掌握突出指标对水分响应特征规律，阐释水分和突出指标内在联系，为低阶煤突出预测和防治提供理论基础。

在我国已探明的煤炭储量中，低阶煤占比达到近一半左右，其具有自然含水率高的特点。水分变化显著影响瓦斯解吸扩散特性及突出指标，而水分对低阶煤瓦斯解吸扩散动力学影响机制研究尚存不足。据此，以三个典型低阶煤矿井沈北矿区蒲河煤矿、铁法矿区小青煤矿和铁法大兴煤矿煤样为研究对象,并选取义马矿区新义煤矿的中阶煤做对比煤样。采用X射线衍射、拉曼和傅里叶变换红外光谱分析技术、小角X射线散射（SAXS）、流体侵入法和瓦斯吸附/解吸试验分析了试验煤样的化学结构、孔隙结构和瓦斯时变扩散动力学特性。结果表明低阶煤样的芳构化程度相较于对比煤样较低，但含氧官能团含量较高。SAXS试验结果表明低阶煤的中孔较为发育。不同含水率（0%~16.8%）试验煤样的吸附/解吸试验结果表明，水分子和甲烷分子在煤体中存在竞争吸附关系，随着煤样含水量的增加，瓦斯解吸量减少，但其影响程度会逐衰弱。且相较于对比煤样，低阶煤样受水分的影响较大。通过分析水分对低阶煤瓦斯时变扩散特性的影响发现，低阶煤样中含水率的增加降低了扩散系数，减缓了时变扩散系数衰减的速率，也减少了时变扩散系数衰减至0的时间。此外，建立煤矿复杂地层突出煤层（低阶煤）瓦斯抽采效果评价指标体系，提出突出指标敏感性和临界值的确定方法。