A new approach in physical modeling for velocity anisotropy studies

Abstract

Special automated equipment was constructed for ultrasonic velocity measurements at various incidence angles of waves that is necessary for estimation of anisotropy parameters of rocks. The equipment includes a hydraulic press for simulation of vertical pressure in the Earth at a range up to 40 MPa, and a computer-controlled positioning system that provides precise independent positioning of the ultrasonic source and receiver. This setup enabled us to perform reliable velocity measurements at the angle interval from 15° to 90° and an additional single measurement at 0°. The minimum step of a transducer position in the 15°–90° range is 8.1’. As an example for the anisotropy study, we performed physical modeling of wave propagation in an artificial sample of transversely isotropic (TI) symmetry, which represents a model of fractured rock. Using an experimental setup, we acquired P-wave velocity data for a plate-stack model with a vertical axis of symmetry formed by acrylic 1-mm-thick sheet plates. Using measured velocities, we estimated Thomsen’s anisotropy parameters ε and δ, and got dependence between the velocity of P-waves and the symmetry axis of the model. In our oncoming research, the upgraded Ultrasonic Measuring System will be supplemented by multicomponent transducers similar to those described in Chichinina et al. (2009), which allow simultaneous recording of P, SV and SH waves at each data point.