液态CO2冻结时间对煤体孔隙结构的影响试验研究
Experimental study on effect of freezing time of liquid CO2 on pore structure of coal
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摘要: 为促进低透气性煤层瓦斯抽采，优化注液态CO2冻融致裂煤层增透促进瓦斯抽采技术，以常村煤矿为研究背景，利用核磁共振、超声波检测等手段，分析了不同液态CO2冻结时间下煤体孔隙结构的演化及损伤机理。研究结果表明：冻融50 min后煤样宏观裂隙变化逐渐明显；随着致裂时间的增加，煤体横波与纵波均逐渐降低，纵波和横波下降率范围分别为5.55%～34.33%、3.72%～17.44%；煤体中各尺寸孔隙逐渐发育，全孔T2谱面积增长率从28.67%升至61.49%，煤体孔隙连通性加强，有利于提高煤体的渗透性。Abstract: In order to promote gas drainage in low-permeability coal seams, implement the optimization of enhancing permeability and promoting gas drainage technology by liquid CO2 injection into freeze-thaw cracked coal seams, taking Changcun Coal Mine as the research background, using nuclear magnetic resonance, ultrasonic detection and other methods, the evolution of coal pore structure and damage mechanism under different freezing times of liquid CO2 are analyzed. The research results show that the macroscopic cracks of the coal sample gradually change significantly after freezing and thawing for 50 minutes. With the increase of the fracture time, the shear and longitudinal waves of the coal body gradually decrease, and the reduction rates of longitudinal and shear waves are in the range of 5.55% to 34.33% and 3.72% to 17.44% respectively; pores of various sizes in the coal body gradually develop, and the growth rate of full-pore T2 spectrum area increased from 28.67% to 61.49%, and the pore connectivity of the coal body was strengthened, which was conducive to improving the permeability of the coal body.
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