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<p>Spontaneous imbibition (SI) is a crucial process in coal-seam water-injection, exerting a significant influence on the effectiveness of water injection. The migration law and occurrence characteristics of water within coal pores during SI remain unclear, and existing models fail to characterize imbibition behavior within coal with a complex pore structure. In this study, two coal types with bedding angles of 0°, 45°, and 90° were selected for SI experiments. Water migration and occurrence characteristics were elucidated using contact angle measurements and nuclear magnetic resonance (NMR) imaging analyzers. A pore-fracture-bedding coupled kinetic model was established based on NMR relaxation principles. The results indicated that water content follows binomial-correlated exponential growth over time. The process was divided into three stages by imbibition rate and bedding effects: rapid imbibition, slow diffusion, and stable saturation. Seepage pores and fractures constituted primary water reservoirs, while adsorption pores facilitate inter-regional water exchange. The imbibition capacity of bituminous coal was approximately twice that of anthracite, with wetting front propagation along bedding planes, whereas anthracite shows non-directional distribution. Bedding angle dictated wetting extent and spatial heterogeneity, with imbibition height and water content ordered as 0° &lt; 45° &lt; 90°. The standard deviations and multifractal parameters for 0° and 90° specimens exceeded those of 45°, confirming that boreholes drilled parallel/perpendicular to bedding significantly increase water distribution heterogeneity. The proposed kinetic model accurately describes imbibition behavior in pore-fracture-bedding coupled coal. This work advances understanding of SI mechanisms and provides theoretical support for safe water-injection and gas hazard prevention in deep coal seams.</p>

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Study on Water Spontaneous Imbibition Migration Law and Occurrence Characteristics in Coal-Seam Water-Injection Process

  • 期刊论文

  • 发表日期：

    2026年4月10日

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  • Zijian Yu,
  • Yangfeng Zheng,
  • Cheng Zhai,
  • Zhengzheng Tang,
  • Mingkun Luo,
  • Hexiang Xu,
  • Yu Wang,
  • Yongshuai Lai,
  • Hongyang Xu,
  • Lihu Hou,
  • Tong Zhang

摘要

Spontaneous imbibition (SI) is a crucial process in coal-seam water-injection, exerting a significant influence on the effectiveness of water injection. The migration law and occurrence characteristics of water within coal pores during SI remain unclear, and existing models fail to characterize imbibition behavior within coal with a complex pore structure. In this study, two coal types with bedding angles of 0°, 45°, and 90° were selected for SI experiments. Water migration and occurrence characteristics were elucidated using contact angle measurements and nuclear magnetic resonance (NMR) imaging analyzers. A pore-fracture-bedding coupled kinetic model was established based on NMR relaxation principles. The results indicated that water content follows binomial-correlated exponential growth over time. The process was divided into three stages by imbibition rate and bedding effects: rapid imbibition, slow diffusion, and stable saturation. Seepage pores and fractures constituted primary water reservoirs, while adsorption pores facilitate inter-regional water exchange. The imbibition capacity of bituminous coal was approximately twice that of anthracite, with wetting front propagation along bedding planes, whereas anthracite shows non-directional distribution. Bedding angle dictated wetting extent and spatial heterogeneity, with imbibition height and water content ordered as 0° < 45° < 90°. The standard deviations and multifractal parameters for 0° and 90° specimens exceeded those of 45°, confirming that boreholes drilled parallel/perpendicular to bedding significantly increase water distribution heterogeneity. The proposed kinetic model accurately describes imbibition behavior in pore-fracture-bedding coupled coal. This work advances understanding of SI mechanisms and provides theoretical support for safe water-injection and gas hazard prevention in deep coal seams.