Determinations of the multifractal characteristics of the pore structures of low-, middle-, and high-rank coal using high-pressure mercury injection

Abstract

The multifractal characteristics of pore structures of low-, middle-, and high-rank coals were analyzed in this study based on the results of high-pressure mercury injection analysis and multifractal theories. The results showed that coal pore structures exhibit multifractal behavior, and were much affected by coalification degrees. For example, it was observed that the Hurst Index (H), information dimension D1, and correlation dimension D2 decreased with increases in the coalification degree. Also, the spectrum width increased, indicating greater local fluctuations of the pore size distributions (PSDs), narrower distribution intervals, enhanced heterogeneity, and reduced pore connectivity. Micropores and mesopores have opposing effects on the multifractal characteristics of pore structures. It has been found that increases in the percentage of mesopores lead to better pore connectivity and more homogeneous pore structures. In addition, increases in mineral content and Mad lead to better connectivity and more uniform pore structures. However, increases in vitrinite content results in decreased pore connectivity, and the complexity of pore structures tends to increase. Also, increases in inertinite content reduce the heterogeneity of the low value regions of the pore volumes, resulting in decreases in the complexity of the overall pore structures.