Resonant ultrasound spectroscopy of horizontal transversely isotropic samples

Abstract

Most crustal rocks present some amount of directional dependence of seismic speeds, particularly mudstones (also termed "shales"). Hence, accurate imaging of the subsurface requires anisotropic models and integration of rock physics information in order to constrain the inherent nonuniqueness of the inversion from seismic data. Resonant ultrasound spectroscopy provides estimates of the full anisotropic stiffness tensor from resonant frequencies of geological core samples, along with a measure of intrinsic attenuation. We have developed new functionality to existing codes which enable horizontal transversely isotropic samples to be analyzed. We compared and discussed estimations of the elastic properties of mudstone samples with hexagonal symmetry; one sample was drilled parallel and one perpendicular to the layering. While spatial heterogeneity in the mudstone prevented a direct correlation of the elastic parameters of each sample, time-of-flight measurements reveal frequency dispersion of the elastic parameters that is consistent between the samples.