Experimental study on the acoustic wave propagation characteristics of bedding shales under changes in temperature and pressure

To determine the acoustic wave propagation characteristics of bedded shales under different confining pressures and temperatures, shales from the Longmaxi Formation in the Sichuan Basin are taken as research objects. Based on ultrasonic experiments, the acoustic wave propagation properties of shales with different bedding angles are investigated. The effects of the confining pressure, temperature, and bedding angle on the acoustic velocity, attenuation coefficient, and acoustic anisotropy coefficient are analyzed. Based on the results, an acoustic velocity prediction model for bedded shales considering the confining pressure, temperature, and bedding angle is established. The experiments show that, for confining pressures from 0 to 50 MPa and temperatures from 20 to 100 °C, the acoustic velocity of the shales increases with increasing confining pressure and decreases with increasing temperature and bedding angle. The attenuation coefficient of the shales exhibits a decreasing trend with increasing confining pressure, but increases with increasing temperature and bedding angle. The acoustic anisotropy coefficient of shale gradually decreases with increasing confining pressure, but increases with increasing temperature and bedding angle. The acoustic velocity prediction model for in-situ bedded shales established in this study has a high level of accuracy. The relationship between the acoustic anisotropy coefficient and the bedding angle is satisfied by a binomial equation. The relationship between the acoustic anisotropy coefficient and the confining pressure and temperature follows a binary linear logarithmic equation