基于X-ray CT与FIB-SEM的无烟煤孔裂隙发育特征

    Characteristics of pores and fractures in anthracite coal based on X-ray CT and FIB-SEM

    • 摘要: 以沁水盆地南部无烟煤为研究对象,基于X-ray CT和FIB-SEM扫描成像试验,构建了无烟煤孔裂隙网络结构模型并提取了关键特征参数,进而对无烟煤孔裂隙发育特征与连通关系开展了定量研究。结果表明:沁水盆地南部无烟煤以孔径小于50 nm的中孔为主,大孔数量较低,显微裂隙和割理对孔隙体积具有较高的贡献;孔隙截面以不规则形状为主,毛管阻力较大;孔隙具有较好的连通性,连通路径较丰富,有利于气体运移和产出;随孔裂隙发育尺度的减小,孔裂隙连通性和渗透率随之降低;对连通性起主要作用的是中孔、显微裂隙和割理;显微裂隙和割理提高了无烟煤微米尺度、毫米尺度孔裂隙的连通性和渗透性,无烟煤纳米尺度以中孔连通为主,限制了无烟煤整体连通性。

       

      Abstract: Taking the anthracite coal in the southerm of Qinshui Basin as the research object, the pore-fracture network models of anthracite coal were established and the key parameters of pore-fracture network were extracted based on the X-ray CT (computed tomography) and focused ion beam scanning electron microscopy(FIB-SEM) imaging experiments. Then, the characteristics of pores and fractures in anthracite coal and their connection relationships were quantitative studied. The results show that the pores of anthracite coal in the southern Qinshui Basin are mainly mesopores with pore size less than 50 nm. Macropore content in anthracite coal is small, and microscopic fractures and cleats make a great contribution to pore volume in anthracite coal. The cross-section is predominantly irregular in shape, which means that the capillary resistance is large. The connectivity of the pores is well with multiple connected paths, which is beneficial to gas migration and output. With the decrease of the scale of pores and fractures, the connectivity and permeability of pore and fracture decrease. Mesopores, microscopic fractures, and cleats play an important role in the connectivity of anthracite coal. The connectivity and permeability of micrometer and millimeter scale pores and fractures in anthracite coal were improved by microscopic fractures and cleats, while the connectivity of nanoscale pores in anthracite coal was dominated by mesopores, which limited the connectivity of anthracite coal.

       

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