Improvement Mechanism of Coal Pore Microstructure by Mineral Variations in the Ultrasonic Cavitation Environment

Ultrasonic technology is regarded as a potential new method for coalbed methane recovery due to its excellent directionality, powerful penetrating power, easy acquisition, and focused sound energy. However, research on ultrasonic excitation fracturing has primarily focused on thermal and vibration effects, with little scientific understanding of ultrasonic cavitation damage to coal pore microstructure based on mineral variations. In this study, a water‐based ultrasonic cavitation device is used to fracture and increase coal permeability. The spatial morphological alterations of pores and mineral structures in coal before and after ultrasonic treatment are investigated using computed tomography scanning, and the changes of parameters, including fractal dimensions, equivalent hole radii, equivalent throat radii, equivalent throat lengths, and coordination numbers prior to and subsequent to ultrasonic treatment, are quantitatively analyzed. The results show that ultrasonic cavitation can improve the coal pore microstructure by facilitating mineral migration, dispersion, and fragmentation. Such an effect can be reflected in the increased number of pores and improved pore connectivity. Ultrasonic cavitation increased the number of pores in coal samples by 1.7 times (4–20 μm), the number of throats by 1.5 times (2–8 μm), and the frequency of coordination numbers surpassing 18 rose from 1 to 12.