Synthetical study on the difference and reason for the pore structure of the No. 3 coal reservoir from the southern Qinshui Basin, China, using mercury intrusion porosimetry, low-temperature N2 adsorption, low field nuclear magnetic resonance, and nuclear magnetic resonance cryoporometry

Abstract

This study aimed to synthetically investigate the pore structure characteristics of coal samples from the southern Qinshui Basin in China, by mercury intrusion porosimetry (MIP), low-temperature N2 adsorption (LTNA), low field nuclear magnetic resonance (LFNMR), and nuclear magnetic resonance cryoporometry (NMRC) methods and to reveal the reasons for the differences in the pore structures of the coal samples. The results show the multimodality of the pore size distribution (PSD) for the different pore diameters from all the samples using MIP and LFNMR, and the bimodality of the PSD of all the samples using LTNA and NMRC. The peak representation in the micropores and transition pores through MIP is generally consistent with that of LTNA, LFNMR, and NMRC, and the peak representation of the PSD in the micropores through MIP is consistent with that of LFNMR. Owing to the differences in the analysis principles and the calculation models from the different analysis methods applied, clear differences are observed in the total volume of the transition pores and micropores based on MIP, LTNA, LFNMR, and NMRC. The anthracitic samples have better connectivity in terms of the PSD than that of the semianthracitic and low-volatile bituminous samples. As revealed through a synthetic analysis, abundantly disconnected transition pores and micropores, as well as poorly connected micropores, occur in coal, particularly in semianthracite and low-volatile bituminous coal. The difference in the PSD between the different coal samples based on the different analysis methods applied is synthetically controlled based on Ro,max, the mineral content in the coal, and the burial depth of the coal samples.