Correlation mechanism between the law of ultrasonic propagation in coal samples and the migration of water

In order to reveal the correlation mechanism between the law of ultrasonic propagation and water migration. A simulation method for displaying the entire process of multi-field coupling ultrasonic excitation, propagation, and reception based on CT scanning reconstruction of the coal pore–fracture structure model is proposed. A porous medium water migration-ultrasonic wave propagation calculation model is constructed by introducing the water-injected coal porous medium water migration calculation model into the ultrasonic propagation calculation process. In the simulation analysis, the coal sample matrix and minerals reconstructed by CT scanning are regarded as homogeneous elastic materials, and the contribution of water migration to the elastic parameters is characterized in the form of equivalent parameters. The pore fracture is regarded as a pressure acoustic fluid, and the equivalent parameter method is used to characterize the water–gas distribution in the pore fracture. The electrostatic coupling solid mechanics and solid mechanics coupled pressure acoustics mode are used to simulate the propagation process of the ultrasonic wave excited by the ultrasonic transducer in the water-injected coal sample, thereby revealing the law of ultrasonic wave propagation in the water-injected porous medium. Research results show that the transmission rate of the ultrasonic wave decreases when the ultrasonic wave propagates to the location of the mineral, and the mineral transmits part of the displacement energy of the ultrasonic wave and partly reflects this energy. The first position reached during the ultrasonic propagation is the position where the fractures are slightly obstructed followed by after reflection, superposition, and finally full distribution. The water accelerates the propagation velocity of ultrasonic waves. However, the capability of ultrasonic waves to pass through the fractures slightly contributes to the presence of water inside the fractures and mainly depends on whether the migration of the coal matrix water covers the fracture area.