Quantitative characterization of void and demineralization effect in coal based on dual-resolution X-ray computed tomography

The in-depth understanding of storage and migration of coalbed methane (CBM) requires the detail characterization of the void system in coal seams. In this study, the multi-scale structures of coal samples from No. 3# coal seam in Mabidong Block in the southern Qinshui Basin are characterized by a dual-resolution X-ray micro-CT, in which the low-resolution CT is applied to scan the coal samples at core scale, and the high-resolution CT is applied to scan the coal samples at micro-scale. Based on the scanning at two scales, the detail structures of coal samples are reconstructed with the image processing technique, which realizes the multi-scale qualitative and quantitative characterization. The results show that the No. 3# coal seam of Mabidong Block in Qinshui Basin develops multi-scale pore structures. The void volume is dominated by micro-fractures (type C) and meso-pores (type E) at core and micro-scales, respectively. Coal presents a high heterogeneity, and the removal of minerals results in void connectivity enhancement of several orders of magnitude.