Microstructural remodeling via mineral migration under ultrasonic cavitation: Key to enhanced methane flow in coal

Ultrasonic treatment not only alters coal porosity but also promotes the migration, dispersion, and fragmentation of host minerals, driving reorganization of the flow network. To reveal the synergistic mechanisms of pore modification and mineral effects at the microscale, this study combines experiments (fluid intrusion, digital core reconstruction, electron microscopy, and X-ray imaging) with numerical simulations to investigate coal microstructure and permeability evolution under different ultrasonic power levels. Focusing on elucidating the dual modification mechanism of ultrasonic cavitation: direct pore structure alteration and indirect effects mediated by mineral disintegration. Results show that ultrasonic treatment significantly enhances mineral particle migration and refinement, with effects strongly dependent on power intensity. As power increases, mineral particles disperse and pores are reconfigured, exhibiting enlarged apertures and greater heterogeneity, leading to improved permeability. BET and fractal analyses indicate a transition from slit-like to more open pore structures. At 1100 W, permeability reaches 8.26 times that of untreated coal. XRD results confirm depolymerization of organic microcrystals and reduced mineral crystallinity, while EDS reveals more dispersed distributions of elements such as Al and Si. Overall, ultrasonic treatment reconstructs coal pore structures across scales through a dual mechanism of direct disturbance and mineral regulation, enhancing connectivity and permeability.