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<p>Accurate pore-size characterization in coal is crucial for optimizing energy recovery processes and improving predictions of gas storage, transport, and environmental impact. In this study, nuclear magnetic resonance cryoporometry (NMRC) and NMR T2 relaxometry were employed to non-destructively characterize the microporosity pore-size distribution (PSD) based on the phase behavior of confined fluids and to determine the surface relaxivity of coal microporosity. By tracking the melting and freezing transitions of water within the porous matrix of nanoporous materials under controlled temperature variations, NMRC exploits the melting-point depression phenomenon to accurately obtain pore diameters ranging from a few nanometers to several hundreds of nanometers. Low-field NMR measurements were performed using the Carr–Purcell–Meiboom–Gill (CPMG) pulse sequence to acquire transverse relaxation time (T2) distributions, enabling the analysis of non-freezing water within different pore populations across a wide range of temperatures. The resulting signal attenuation profiles were correlated with pore sizes by calibrating the NMRC PSD and T2 distribution curve, allowing estimation of the surface relaxivity. A custom experimental setup enabled in situ temperature calibration and precise thermal control throughout the experimental process. The approach was applied to coal from the Lorraine–Saar basin, revealing distinct micro- and mesopore populations. NMRC thus offers a robust, non-invasive technique for accurately quantifying the micropore structure of coal. In addition, a complementary T2 experiment performed during controlled drying was used to investigate water-evaporation mechanisms in coal, enabling non-destructive monitoring of moisture redistribution across different pore scales.</p>

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Pore-Size Distribution of Coal Characterized by NMR Relaxometry and Cryoporometry

  • 期刊论文

  • 发表日期：

    2026年3月22日

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  • Minchuan Jiang,
  • Tien Dung Le,
  • Didier Stemmelen,
  • Sébastien Leclerc,
  • Irina Panfilov

摘要

Accurate pore-size characterization in coal is crucial for optimizing energy recovery processes and improving predictions of gas storage, transport, and environmental impact. In this study, nuclear magnetic resonance cryoporometry (NMRC) and NMR T2 relaxometry were employed to non-destructively characterize the microporosity pore-size distribution (PSD) based on the phase behavior of confined fluids and to determine the surface relaxivity of coal microporosity. By tracking the melting and freezing transitions of water within the porous matrix of nanoporous materials under controlled temperature variations, NMRC exploits the melting-point depression phenomenon to accurately obtain pore diameters ranging from a few nanometers to several hundreds of nanometers. Low-field NMR measurements were performed using the Carr–Purcell–Meiboom–Gill (CPMG) pulse sequence to acquire transverse relaxation time (T2) distributions, enabling the analysis of non-freezing water within different pore populations across a wide range of temperatures. The resulting signal attenuation profiles were correlated with pore sizes by calibrating the NMRC PSD and T2 distribution curve, allowing estimation of the surface relaxivity. A custom experimental setup enabled in situ temperature calibration and precise thermal control throughout the experimental process. The approach was applied to coal from the Lorraine–Saar basin, revealing distinct micro- and mesopore populations. NMRC thus offers a robust, non-invasive technique for accurately quantifying the micropore structure of coal. In addition, a complementary T2 experiment performed during controlled drying was used to investigate water-evaporation mechanisms in coal, enabling non-destructive monitoring of moisture redistribution across different pore scales.