基于NMR技术的超声波频率对煤体激励致裂效果的影响

为了深入研究超声波频率对煤体激励致裂效果的影响，利用超声波发生仪对原始煤样进行致裂实验，并利用低场核磁共振设备NMR设备对煤样进行测量，通过分析弛豫时间T₂曲线，深入研究煤样致裂前后孔隙结构的变化。研究结果表明:超声波可以有效改善煤体的孔隙结构，经超声波激励致裂后，煤样内部的孔隙数量增多，总孔隙率、有效孔隙率及渗透率均明显增大；同时，煤样内部小孔数量的增长率与超声波频率呈负相关关系，中孔和大孔数量、总孔隙率增长率、有效孔隙率及渗透率的增长率与超声波频率均呈正相关关系。研究结果为煤储层超声波致裂增透技术奠定理论基础。 

Effect of NMR technology-based ultrasonic frequency on stimulated cracking of coal

In order to further study the effect of ultrasonic frequency on the stimulated cracking effect of coal, the paper conducted the crack experiment on the original coal samples by using the ultrasonic generation meter, and measured the coal by using the NMR equipment through analyzing the T₂ curve, the changes of pore structure before and after coal sample cracking were deeply studied. The results show that the pore structure of coal can be effectively improved by the ultrasonic wave. After the crack induced by the ultrasonic wave, the pore quantity inside the coal increased and the total porosity, effective porosity and permeability all increased significantly. Meanwhile, the growth rate of the number of small pores in coal is negatively correlated with the frequency of ultrasonic wave, and the growth rate of the number of medium and large pores, total porosity, effective porosity and permeability are positively correlated with the frequency of ultrasonic wave. The results of this study provide a good theoretical value for ultrasonic stimulation to crack coal seam and reduce the difficulty of coal seam gas extraction.