Acoustic characteristics and fracture toughness of shale in Longmaxi formation

In order to better guide the development of shale gas in the Sichuan basin, taking the shale from Silurian Longmaxi formation in southern Sichuan as the research object, the acoustic characteristics and fracture toughness were studied. Among them, the transmission method is used to measure P-wave and Swave velocities, and the fracture toughness method is the Cracked Chevron Notched Brazilian Disc(CCNBD) recommended by ISRM. The results show that the fracture toughness is 0.474 4 ～0.875 2 MPa·m~(0.5), which has significant anisotropic characteristics; the vertical and transverse wave velocity of shale shows a good positive correlation. The acoustic velocity of shale increases with the increase of its volume density, showing a positive correlation. The frequency of acoustic wave is positively correlated with the velocity and attenuation coefficient of acoustic wave. Fracture toughness is positively correlated with acoustic velocity and impedance, and negatively correlated with attenuation coefficient.