A new approach in physical modeling for velocity anisotropy study

Abstract

Special automated equipment is constructed for ultrasonic velocity measurements at various incidence angles of waves that is necessary for estimation of anisotropy parameters of rocks. The equipment includes hydraulic press for simulation of vertical pressure in the Earth, at a range up to 40 MPa and computer controlled positioning system that provides precise independent positioning of ultrasonic source and receiver. This setup enables us to perform reliable velocity measurements at the angle interval from 15° to 90° and additional single measurement at 0°. The minimum step of a transducer position in 15°-90° range is 8.1'. As an example on anisotropy study, we perform physical modeling of wave propagation in artificial sample of transversely isotropic (TI) symmetry, which represents a model of fractured rock. Using experimental setup, we acquire P-wave velocity data for plate-stack model with vertical axis of symmetry formed by acrylic 1 mm thick sheet plates. Using measured velocities, we estimate Thomsen’s anisotropy parameters e and δ, and get dependence between the velocity of P-waves and 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.