Velocity dispersion in rocks: A laboratory technique for direct measurement of P-wave modulus at seismic frequencies

Fluid saturated rocks exhibit a dependence of acoustic velocities on frequency, which is called velocity dispersion. For some rocks, e.g., shales, velocity dispersion is rather strong and has to be taken into account when interpreting and comparing data from seismic surveys, sonic logs, and ultrasonic measurements on core plugs in the laboratory. In this work, a new laboratory technique has been developed that allows the direct measurement of the P-wave modulus at seismic frequencies from which the P-wave velocities can be derived. Together with ultrasonic velocity measurements that are carried out simultaneously, the P-wave velocity dispersion between seismic and ultrasonic frequencies is obtained.