中变质煤小分子相对煤的吸附及渗流特性影响

为研究煤中小分子对煤的瓦斯吸附及流动特性的影响,采用四氢呋喃溶剂萃取煤中可溶有机小分子,得到萃取后煤样(残煤)。对原煤和残煤分别进行甲烷等温吸附、解吸实验和径向渗流实验;同时,采用氮气吸附法测试了它们的孔隙结构参数。结果表明,残煤的饱和吸附量a值低于原煤,吸附常数b值增大,萃取小分子降低了煤对甲烷的吸附能力,提高了低压段(<4 MPa)煤对甲烷的解吸速率;原煤的孔体积和平均孔径高于残煤,比表面积和微孔孔体积却减少;萃取后,煤粒表面传质阻力和扩散阻力均减小,残煤甲烷解吸速率和解吸量均高于原煤;同一渗流条件下,残煤的渗透率明显高于原煤。分析认为,煤中部分小分子被溶解后,煤孔隙结构的改变,降低了煤对瓦斯的吸附能力,减小了甲烷在煤粒中的内外扩散阻力,扩大了瓦斯在煤中的流动通道,改变了煤层储运特性,为煤储层的化学增透提供依据。

Effect of small organic molecule in mid-metamorphism coal on gas adsorption and flow characteristics

Two bituminous coals were extracted with tetrahydrofuran (THF) solvent at 50 ℃ and atmospheric pressure by microwave-assisted extraction. The experiments of methane sorption isotherms, desorption and radial seepage for raw coals and their residues were carried out. The results indicate that the ability to adsorb methane is reduced after extraction of the small organic molecule, and the methane desorption rate is improved. Pore volume and average pore diameter of raw coal is higher than that of the residual coal,while the specific surface area and micropore volume are reduced. After solvent extraction, the desorption velocity and desorption quantity are higher that of raw coal because the resistances of surface mass transfer and diffusion are reduced. Permeability of residues is higher than that of raw coal under the same seepage condition. The gas adsorption is lowered, the internal and external diffusion resistance of methane is decreased, and the gas flow channel in coal is expanded. These behaviors are caused by the change of coal pore structure after dissolving some small organic molecule in coal. Therefore, solvent extraction can change the storage and transportation of coal seam features, which provides the basis for improving the permeability of the coal reservoir with chemical methods.