Abstract: This study is to simulate the damage of layered shale under ultrasonic vibration with different bedding dip angles by establishing a discrete element model of layered shale with numerical simulation methods so as to explore the feasibility of ultrasonic vibration-assisted shale reservoir stimulation. The results show that the angle between the vibration direction and the bedding surface has a significant influence on the propagation of ultrasonic vibration.The smaller the angle, the more microcracks generated.The racks are mainly concentrated near the vibration stress, and fewer microcracks are generated in areas further away from the vibration source.Ultrasonic vibration has an obvious impact on the strength of layered shale, inducing a large number of microcracks inside the shale, and the change of microstructure and physical properties of the shale, also the uniaxial compressive strength and elastic modulus are significantly reduced. This study provides a theoretical basis for reservoir stimulation of layered shale using ultrasonic vibration.

Key words: layered shale, ultrasonic vibration, uniaxial compressive strength, numerical simulation, discrete element model