Abstract Water-injected technique was once considered as an effective way to solve the gas-induced problems in the mining industry, but has been stagnant due to its unstable conditions. A systematic knowledge on the micro-mechanism of water injection into coal seams is beneficial to better understand water-based techniques. However, the laboratory investigations considering the engineering background of water injection as well as the pore morphology of targeted coal seam have been rarely studied. In this paper, characterization of pore morphology and the effect of injected water on gas desorption characteristic were carried out using pore structure analyzers (N2 adsorption and mercury intrusion methods), high-resolution scanning electron microscopy and a home-made instrument (water-injecting desorption test). The pore morphology results from pore size distribution, fractal dimension, pore shape and connectivity indicate that the essential configuration of pore structure is well-developed larger pores containing abundant smaller pores with extensive distribution of constricted pores that are inaccessible to fluid migration. The influence of pore morphology on desorption process may be attributed to the microporous constrictions with non-effective pores, which are geometrically interpreted by pore blocking mechanism. The desorption test results show the total desorption volumes and initial effective diffusion coefficient have the reduce rates of 26.65% and 38% with the moisture content increasing from dry to 1.8% while have a little change as moisture increases (1.8%–11.2%), demonstrating the obstruction of water molecule on gas desorption pathway and the existence of extremity moisture content. Water injection has a remarkable effect on the average desorption rates in the initial period of 10 min; however, the ultimate desorption volume of 0.81 mL/g with higher moisture content of 11.2% is not sensitive to adsorption equilibrium pressure. Moreover, combined with the mature water-injected technique in the actual coal seam, a conceptual design was summarized to consider the effect of the constricted pore morphology on the interactions of “water-gas-coal”, which may demonstrate the micro-mechanism of gas migration in the far water-injected coal seam. Meanwhile, in the near water injection zone, due to more energetic gas molecules forming gas bubble in the aqueous condition, nucleation appears to be imagined to explain the pressure-insensitive phenomenon. These findings are of great guiding significance to the theoretical studies and field applications of actual water-injected coal seam.

中文翻译：

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含水煤孔隙形态特征及其对甲烷解吸的影响——注水煤层瓦斯运移机理探索

摘要 注水技术曾被认为是解决采矿业瓦斯问题的有效途径，但因条件不稳定而停滞不前。对煤层注水微观机理的系统知识有利于更好地理解水基技术。然而，考虑到注水工程背景以及目标煤层孔隙形态的实验室研究很少被研究。本文利用孔隙结构分析仪（N2 吸附法和压汞法）、高分辨扫描电镜和国产仪器（注水法）对孔隙形貌进行表征以及注入水对气体解吸特性的影响。解吸试验）。由孔径分布、分形维数、孔形状和连通性得出的孔形态表明，孔结构的基本构型是发育良好的大孔，其中包含丰富的小孔，以及广泛分布的狭窄孔，流体无法迁移。孔隙形态对解吸过程的影响可能归因于具有无效孔隙的微孔收缩，这是通过孔隙阻塞机制进行几何解释的。解吸试验结果表明，总解吸体积和初始有效扩散系数随水分含量从干燥增加到1.8%，降低率分别为26.65%和38%，而随着水分的增加（1.8%~11.2%）变化不大，证明水分子对气体解吸途径的阻碍和末端水分含量的存在。注水对10 min初始阶段的平均解吸速率有显着影响；然而，0.81 mL/g 的最终解吸体积和 11.2% 的较高水分含量对吸附平衡压力不敏感。此外，结合实际煤层中成熟的注水技术，总结出考虑收缩孔隙形态对“水-气-煤”相互作用的影响的概念设计，这可能证明了水-气-煤相互作用的微观机制。远注水煤层瓦斯运移. 同时，在近注水区，由于更多的高能气体分子在水相条件下形成气泡，成核似乎被认为可以解释压力不敏感现象。这些发现对实际注水煤层的理论研究和现场应用具有重要的指导意义。