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显微组分控制下富惰质组煤微观裂隙特征及裂隙扩展机理

Microfracture characteristics and propagation mechanisms in inertinite-rich coal controlled by macerals

  • 摘要: 为阐明煤中显微组分对煤微观裂隙发育与扩展的控制机理,以鄂尔多斯盆地延安组煤层为研究对象,开展了系统的实验与数值模拟研究。通过光学显微镜和扫描电镜观测,定量分析不同显微组分中裂隙的密度分布与延展特征; 结合单轴压缩实验与数值模拟方法,揭示应力加载过程中裂隙的演化规律及煤中显微组分控制机制。结果表明:非穿层显微裂隙几乎全部发育于镜质组内,而穿层裂隙的分布形式更为复杂; 镜质组内裂隙密度较高,且随条带厚度减小而增大,惰质组内因其条带塑性较强,其裂隙密度与条带厚度的相关性较弱; 煤中显微组分条带平均厚度的增加有利于裂隙的延伸,而惰质组含量的增大则抑制穿层裂隙扩展; 在应力加载过程中,裂隙演化呈现“镜质组内萌生→惰质组内扩展→裂隙连通”的阶段性特征,在萌生阶段镜质组以拉伸破坏为主,在扩展—连通阶段镜质组转为压剪破坏,惰质组则仍以拉伸破坏为主。揭示了不同煤中显微组分在裂隙演化各阶段的力学响应差异,可为煤层气储层评价与瓦斯灾害防治提供理论依据。

     

    Abstract: To elucidate the controlling mechanisms of macerals in coal on the development and propagation of microfractures in coal, a systematic combined experimental and numerical simulation study was conducted on coal seams from the Yan'an Formation in the Ordos Basin. Fracture density distribution and propagation characteristics within different macerals were quantitatively analyzed using optical microscopy and scanning electron microscopy. Uniaxial compression tests integrated with numerical simulations were employed to reveal the evolutionary patterns of fractures under stress loading and the associated control mechanisms of macerals in coal. The results show that non-through-going microfractures are almost exclusively developed in vitrinite, whereas through-going fractures exhibit more complex distribution patterns. Fracture density in vitrinite is relatively high and increases with decreasing band thickness, while in inertinite, it shows a weak correlation with band thickness due to the higher plasticity of inertinite bands. An increase in the average thickness of maceral in coal bands facilitates fracture propagation, whereas a higher inertinite content suppresses the propagation of through-going fractures. Under stress loading, fracture evolution follows a stage-wise sequence of "initiation within vitrinite→propagation within inertinite→fracture coalescence". During the initiation stage, vitrinite is predominantly subject to tensile failure; in the propagation-coalescence stage, vitrinite transitions to compression-shear failure, whereas inertinite remains dominated by tensile failure. This study reveals the distinct mechanical responses of different macerals in coal across the stages of fracture evolution, providing a theoretical basis for coalbed methane reservoir evaluation and gas disaster prevention.

     

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