Accurate characterization of coal pore and fissure structure based on CT 3D reconstruction and NMR

In order to accurately achieve the full-scale characterization of coal pore and fissure structure, a comprehensive characterization method based on Computed Tomography (CT) 3D reconstruction, Nuclear Magnetic Resonance (NMR) T2 spectrum and Nuclear Magnetic Imaging (NMI) are proposed. CT scanning and NMR experiments are carried out on the samples of gas coal and anthracite to verify this method. And the characteristics of pore size distribution (PSD), porosity and permeability are studied. It is found that the main seepage channels can be obtained by CT 3D reconstruction, and that the observation defect of CT scanning can be compensated by NMI because micro seepage pores and adsorption pores can be visualized. Furthermore, CT 3D reconstruction results indicate that the larger the pore size, the smaller the number of pores, and the larger the porosity component while the NMR T2 spectrum of pore size distribution show that the porosity component of micro adsorption pores is largest. With the advantage of CT macro-scale observation and NMR micro-scale observation combined, porosities are calculated accurately. Besides, seepage characteristics observed in the NMR experiments under different water injection pressures are analyzed, and the results are consistent with the analysis results of the CT 3D reconstruction of coal connectivity.