Study on Microscopic Pore Structures of Coal Based on Nuclear Magnetic Resonance Technology

To study the microscopic pore structure characteristics of coal, the pore types, connectivity and pore size distribution features of coal samples are monitored by nuclear magnetic resonance (NMR). Combining the results of X-ray diffraction (XRD) and co-mputed tomography(CT) scanning, the internal phase composition, mineral composition and pore morphology of coal are also sum-marized. Results show that: various mineral compositions are found in the investigated coal, including kaolinite, calcite and pyrite; the minerals mainly include in the coal cleat system; the spectrum of T₂ transverse relaxation time of the tested coal is a typical triplet curve; according to the T₂ value, three times intervals of 0.5 ms to 5 ms, 5 ms to 100 ms, and >100 ms represent the features of adsorption pores, seepage pores, diffusion pores, respectively. The T₂ cutoff value falling in the range of 10 ms to 20 ms demonstrates that the measured samples have a highly developed microscopic pores and a relatively developed pore structure. The test results of NMR are consistent with the results of 3D visualization analysis of CT scanning, and NMR can make up the deficiency of CT scanning on the micro scale by showing the internal pore characteristics of coal samples.