Comparison of Monofractal and Multifractal Methods in Characterizing Coal Pore Structures
DOI:
https://doi.org/10.63313/FE.2010Keywords:
Coal Pores, Fractal Dimension, Monofractal, MultifractalAbstract
Coal pore structures commonly exhibit significant heterogeneity, and fractal theory provides an effective tool for the quantitative characterization of such complex structures. Regarding multi-scale pore data acquired by CO2 adsorption (micropores), N2 adsorption (mesopores), and mercury intrusion porosimetry (macropores), monofractal and multifractal methods differ fundamentally in their computational principles and characterization approaches.This review discusses three classic models for monofractal dimension: the Sierpinski model based on CO2 adsorption data, the Frenkel–Halsey–Hill (FHH) model based on N2 adsorption data, and the Menger sponge model based on mercury intrusion porosimetry (MIP) data. It also introduces the calculation methods for multifractal spectral parameters derived from the box-counting method, including the generalized dimension spectrum D(q), the multifractal singularity spectrum f(α), and the spectral width Δα. On this basis, a systematic comparison of the two approaches is conducted from multiple perspectives. The monofractal dimension quantifies the overall average complexity of coal pore structures as a single scalar value, offering computational simplicity and high efficiency, which renders it suitable for rapid screening of large sample sets and global evaluation of pore complexity. In contrast, the multifractal approach enables a detailed characterization of pore size distribution heterogeneity across different scale intervals and local domains, and is particularly well-suited for high-resolution microstructural analysis of strongly heterogeneous samples, such as tectonically deformed coal. This study provides a theoretical foundation for the rational selection of fractal methods in the characterization of coal reservoir pore structures.
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