NMR experiments on the migration characteristics of water in bedding-bearing low rank coal

Coal seam water injection is an effective technique for dust reduction in coal mines. Imbibition is an important means of water transport in coal seams and is influenced by coal bedding. The spatial distribution of water in the seepage process was obtained, and the spontaneous seepage characteristics and water transport mechanisms of coals containing different layered angles were revealed by NMR. Results show that the bedding mainly serves as the water flow channels in the imbibition. When the angle increases, the imbibition rate of adsorption pores and seepage pores in the early stage decreases. The imbibition is firstly transported to the top quickly along the bedding flow channel, 1.5h for 0 degrees bedding coal sample, 24h for 90 degrees, when the water reached its apex, the curve no longer changed and imbibition proceeded slowly. With the increase of bedding angle, the imbibition equilibrium time increased from 3h to 30h, up to 9 times more, the maximum imbibition rate decreases significantly, reduced from 5.64 g/h to 1.13 g/h, the flow resistance increases, and the remaining capillary force after equilibrium increases from 0.007 Pa to 5.24 Pa. When the capillary force cannot overcome the flow resistance, the imbibition reaches equilibrium.