Abstract Hydraulic technology is commonly used in enhanced coalbed methane recovery. This technology also causes the coal to remain in a high water content state for a long time, and the expansive clay inside the coal will swell in this high water content state. However, the swelling characteristics of the expansive clay and its effect on the permeability of the coal under water-saturated conditions are not clear. In this study, comparative experiments were conducted on dry coal, coal treated with 0.5% KCl solution, and water-saturated coal to analyze the swelling characteristics and permeability evolution of anthracite containing expansive clay. The scanning electron microscopy results revealed that the surface of the dry coal was flat and smooth, whereas that of the water-treated coal contained many dark areas with expansions of varying sizes. The swelling rate tests show that the volume of the water-treated coal increased by 12.5% compared to the kerosene-treated coal, which is mainly caused by the hydration swelling of the expansive clay. The low-temperature nitrogen adsorption tests show that hydration swelling can significantly reduce the cumulative pore volume of water-saturated coal, mainly the macropores and mesopores. The seepage tests show that the permeability of the water-saturated coal is lower than that of dry coal under varying effective stresses and gas pressures. The permeability damage rate of the water-saturated coal is significantly higher than that of the KCl solution-saturated coal, which also indicates that the expansive clay has a significant effect on the permeability of coal seams.

中文翻译：

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含水饱和条件下含膨胀粘土的无烟煤膨胀特性及渗透率演化

摘要 水力技术是提高煤层气采收率的常用技术。这种技术也使煤长期保持在高含水状态，煤内部的膨胀粘土会在这种高含水状态下膨胀。然而，膨胀粘土的膨胀特性及其对水饱和条件下煤渗透性的影响尚不清楚。本研究通过对干煤、0.5% KCl 溶液处理煤和水饱和煤进行对比试验，分析了含膨胀粘土无烟煤的膨胀特性和渗透率演化。扫描电镜结果表明，干煤表面平整光滑，而水处理煤表面含有许多大小不一的膨胀暗区。膨胀率试验表明，水处理煤的体积比煤油处理煤增加了12.5%，这主要是由膨胀粘土的水化膨胀引起的。低温氮吸附试验表明，水化膨胀可以显着降低水饱和煤的累积孔隙体积，主要是大孔和中孔。渗流试验表明，在不同的有效应力和瓦斯压力下，水饱和煤的渗透率低于干煤。水饱和煤的渗透破坏率明显高于KCl溶液饱和煤，这也说明膨胀粘土对煤层渗透率有显着影响。