动力冲击对煤岩内部微结构影响的NMR定量表征

Effects of dynamic loads on internal microstructure of coal by nuclear magnetic resonance(NMR)

利用自制落锤式煤岩冲击加载试验装置对原煤与型煤试件分别进行冲击加载试验,并借助核磁共振分析仪获得冲击加载后煤样的T_2谱分布,以分析冲击荷载作用次数、单次冲击能量大小、冲击能量加载顺序、冲击能量的累计效果等因素对煤样内部微结构数量、尺度的影响。结果表明:型煤与原煤试件T_2谱分布存在一定的差异,动力冲击使原煤与型煤试件的微结构数量、尺度均有不同程度的增加,且原煤试件增幅更为明显;煤样内部微结构总数量随着冲击次数、单次冲击能量的增加均呈非线性变化,整体上随着冲击次数的增加呈"高速增加–平缓发展–急速增加"三段式变化,而随着单次冲击能量的增加呈增速越来越快的变化;由于冲击能量阈值与冲击能量吸收率2个相反因素在耦合作用,冲击能量的累计效果可能随单次冲击能量的增加呈先增加后减小变化,冲击能量的累计不能等效为冲击能量的增加;煤样内部微结构总数量对冲击能量由大到小进行加载更为敏感,在工程现场可通过调整施工顺序来达到高效改造储层等目的。

The tests on raw coal and moulded coal specimens under impact loads were performed with the drop hammer impact test device developed in-house. The effects of the number of impact loading,the magnitude of the energy of a single impact,the accumulative effects of impact energy and the energy sequence of impact on the internal micro-structure of coal were studied according to the distribution of T2 spectrum of specimens measured with the nuclear magnetic resonance（NMR） analyzer. The results show that there are some differences between T2 spectrum distributions of raw coal specimen and moulded coal specimen. The quantity and size of internal micro-structure of specimens,especially of raw coal specimens,were increased due to the dynamic loads. The total quantity of internal micro-structure of coal increased nonlinearly with the increase of impact times with a trend of rapid increasing,gentle development and sharp increasing,and increased nonlinearly with the increasing of energy of single impact. Due to the coupling effects of the threshold and absorption rate of impact energy,the accumulative effect of impact loads on internal micro-structure of coal is also nonlinear and has a decreasing trend after the first increase. The accumulative effects of impact loads cannot be simplified as the increasing of the impact energy. The total quantity of internal micro-structure of coal is more sensitive under decreasing cyclic loading than increasing process,so the reservoir can be efficiently stimulated by adjusting the construction sequence in the engineering field.