Abstract The utilization of liquid CO2 for enhanced coalbed methane recovery has great environmental and commercial potential to sink greenhouse gas emissions and enchance CH4 extraction. A comprehensive understanding of mechanical properties and micro-scale changes to coal saturated with liquid CO2 would fill the knowledge gap regarding CO2 utilization and be greatly beneficial to industry. The present study employed extensive experimentation using uniaxial compression test, acoustic emission (AE) monitoring, Brazilian splitting test, scanning electron microscopy, and energy dispersive X-ray diffraction spectrometry to determine the damage features of coal microstructure, mechanical characteristics, failure modes, and minerals variation between original and liquid CO2-saturated coal samples. The pre-existing cracks were enlarged and more cracks were generated in the saturated coal samples than in the raw samples. The liquid CO2-saturated coal samples exhibited larger plastic deformation and lower compressive strength in unstable crack propagation stage and more AE counts in rupture stage than those of unsaturated samples. The average compressive strength and tensile strength of the saturated samples were 21% and 27% lower than that of the raw samples. More ragged failure cracks were formed in the liquid CO2-saturated coal specimens than in the unsaturated coal samples. The failure modes of the saturated coal samples were inclined to ductile fracture as opposed to brittle fracture in the unsaturated coal samples. The width and number of micro-cracks on the saturated samples were both increased, and the amount of partial minerals that filled in the micro-cracks reduced after liquid CO2 saturation, which indicated an interaction between minerals in coal and liquid CO2 during the saturation process.

中文翻译：

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液态CO2-ECBM过程对煤力学特性和微观结构的损伤效应

摘要 利用液态 CO2 提高煤层气回收率在减少温室气体排放和加强 CH4 提取方面具有巨大的环境和商业潜力。全面了解液态二氧化碳饱和煤的力学特性和微观变化，将填补二氧化碳利用方面的知识空白，对工业大有裨益。本研究使用单轴压缩试验、声发射 (AE) 监测、巴西劈裂试验、扫描电子显微镜和能量色散 X 射线衍射光谱法进行广泛的实验，以确定煤微观结构的损伤特征、力学特性、失效模式和原始和液态 CO2 饱和煤样品之间的矿物质差异。与原始样品相比，饱和煤样品中预先存在的裂缝扩大并且产生更多的裂缝。液态 CO2 饱和煤样在不稳定裂纹扩展阶段表现出更大的塑性变形和更低的抗压强度，在破裂阶段表现出比不饱和样品更多的 AE 计数。饱和样品的平均抗压强度和抗拉强度比原始样品低 21% 和 27%。液态 CO2 饱和煤样比不饱和煤样形成了更多的参差不齐的破坏裂纹。饱和煤样的破坏模式倾向于韧性断裂，而不是不饱和煤样中的脆性断裂。饱和样品上微裂纹的宽度和数量均增加，