Damage Characteristics of Ultrasonic Cavitation Erosion on Coal: Enhancing Coal Seam Permeability Through Ultrasonic Cavitation Effects

Abstract

Ultrasonic excitation of coal body is an effective method to improve the extraction rate of low-permeability coal seams. Through different duration ultrasonic cavitation erosion coal body tests, the interrelationships between the mechanical damage and failure characteristics of the coal body are quantitatively characterized, and the failure mechanism of ultrasonic cavitation erosion on the coal body is explored. The results show that with the prolongation of ultrasonic time, the cavitation bubbles produced by the cavitation effect gradually accumulate and grow inside the coal body, and the coal body weakening effect is gradually enhanced. The number of signals in the shear crack region inside the coal body decreases, and the damage form of the coal samples gradually changes from brittle damage to brittle-ductile damage. Through the establishment of different time ultrasonic excitation coal body mechanical damage model, the peak stress error varies in a small range, indicating that the established model can reflect the ultrasonic excitation effect on the evolution of coal body damage. In summary, under the action of ultrasonic excitation at different times, the cavitation effect increases the number of alteration points and the size of alteration pits inside the coal rock, weakens the cementation between the mineral particles, reduces the macroscopic properties of coal, forms a seepage network, and effectively improves the extraction rate of coalbed methane.

Keywords: Ultrasonic cavitation erosion, Mechanical characteristics, Acoustic emission, Law of destruction, Mechanical model