CO fracturing enhances gas permeability by creating a complex network of fractures in coal seams. Crushing serves as the foundation of fracture development, and studying the coal crushing behavior under supercritical CO transient high-pressure fracturing is of great significance to understand fracture evolution and guide precise fracturing. This study utilized a self-built experimental platform for supercritical CO transient high-pressure fracturing to obtain fractured coals at different energy levels. Based on multifractal theory, the relationship between fracturing energy and crushing behavior was studied by laser particle analysis and scanning electron microscopy. The results showed that the volume average particle size (), and the particle sizes at which the cumulative particle size distribution reached 50% (), and 90% () decreased significantly with the increase of fracturing energy. The converted diameter and the crushing work ratio exhibited an exponential relationship with the fracturing energy. The larger the fracturing energy, the smaller the values of the multifractal generalized dimension spectrum parameters (, , and Δ()), the larger the values of the multifractal singular spectrum width (Δα ()), and the denser and more even the particle size distribution of fractured coal. The multifractal parameters and shape coefficients exhibited phased change during the fracturing process. The coal particles progressed from an initial stage with numerous microcracks and fissures to a honeycomb structures with small pores. After the disintegration of the honeycomb structures, agglomerated ultrafine particles were formed. The findings provide a theoretical reference for optimizing the selection of fracturing parameters.

中文翻译：

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超临界CO2瞬态高压压裂煤破碎行为研究

CO 压裂通过在煤层中形成复杂的裂缝网络来提高气体渗透性。破碎是裂缝发育的基础，研究超临界CO瞬态高压压裂下煤的破碎行为对于了解裂缝演化、指导精准压裂具有重要意义。本研究利用自建的超临界CO瞬态高压压裂实验平台，获得不同能级的压裂煤。基于多重分形理论，通过激光颗粒分析和扫描电镜研究了断裂能与破碎行为的关系。结果表明，随着压裂能量的增加，体积平均粒径（）、累积粒径分布达到50%（）和90%（）时的粒径显着减小。换算直径和破碎功比与破碎能呈指数关系。破裂能越大，多重分形广义维谱参数(、、Δ())值越小，多重分形奇异谱宽(Δα())值越大，颗粒越致密、越均匀裂隙煤的粒度分布。多重分形参数和形状系数在压裂过程中表现出阶段性变化。煤颗粒从具有大量微裂纹和裂隙的初始阶段发展到具有小孔隙的蜂窝状结构。蜂窝结构崩解后，形成团聚的超细颗粒。研究结果为优化压裂参数选择提供了理论参考。