Impact of ultrasonic power on evolution mechanism of cavitation effect in water-bearing coal pores microstructure

Ultrasonic waves have been explored for fracturing coal seams to enhance Coalbed Methane (CBM) permeability, yet the underlying mechanics of ultrasonic cavitation are not fully understood. This study investigates the effect of water-based ultrasonic cavitation on coal pores microstructure by employing fluid invasion methods and non-destructive X-ray testing to reconstruct coal pore microstructures. Additionally, numerical simulations of ultrasonic cavitation development were conducted. The research examines how ultrasonic power influence evolution mechanism of cavitation effects in pores microstructure of water-bearing coal. Such insights lay a theoretical groundwork for improved Water-Based Ultrasonic Cavitation Enhanced Coalbed Methane Recovery (WUC-ECBM). Findings suggest that coal pores microstructure with a fully connected pore topology are more conducive to ultrasonic cavitation. As ultrasonic exposure increases, the accumulated waves cause coal pore microstructure cavitation bubbles to oscillate violently and non-linearly, leading to their growth, development, and collapse. This results in high-energy microjets and shockwaves, creating a high-temperature, high-pressure environment (reaching up to 35.69 MPa and 2729.77 K) favorable for improving gas desorption and migration. Ultrasonic power adjusts the cavitation threshold and intensity, facilitating gas migration. This research aims to improve gas desorption and migration in coal by capitalizing on the mechanical, physical, and thermal effects of ultrasonic cavitation. These findings offer theoretical support for the effective implementation of WUC-ECBM.