Experii\iental Deteri\iiination of Elastic Anisotropy of Berea Sandstone, Chicopee Shale and Chelmsford Granite

We use the ultrasonic transmission method to measure P-, SH-, and SV-wave velocities for Chelmsford Granite, Chicopee Shale, and Berea Sandstone in different directions up to 1000 bars confining pressure. The velocity measurements indicate that these three rocks are elastically anisotropic. The stiffness constants, dynamic Young's moduli, dynamic Poisson's ratios, and dynamic bulk moduli of these three rocks were also calculated. These elastic constants, together with velocity measurements, suggest that: (1) Elastic anisotropy is due to the combined effects of pores/cracks and mineral grain orientation. (2) Elastic anisotropy decreases with increasing confining pressure. The residual anisotropy at higher confining pressure is due to mineral grain orientation. INTRODUCTION Most geologic materiais, owing to their possession of foliations (such as bedding) and/or lineations (such as preferred orientation of the long axes of mineral grains), are elastically anisotropic. Instead of two elastic constants in isotropic materials, five, nine, or even more elastic constants are required to describe the elastic properties of these materials. The determination of these elastic constants is essential if we want to properly describe the behavior of elastic waves in these materials. Many papers have been devoted to the experimental aspects of elastic anisotropy of geologic materials (Podio-Lucioni, 1968; King, 1969; Todd et al., 1973; Gregory, 1977; Bachman, 1983; White et al., 1983; Crampin, 1984). In this paper, our primary interest is the determination of anisotropy variation as a function of confining pressure. This paper is also an extension of similar experiments conducted by King (1968, 1969) where elastic properties of Bandera Sandstone, Berea . Sandstone, and Boise Sandstone were measured. In our experiment, we measured the velocity anisotropy of P-, SH-, and SV-waves for Chelmsford Granite, Chicopee Shale, and Berea Sandstone at confining pressures up to 1000 bars; calculated the five independent stiffness constants, two dynamic Young's moduli, three dynamic Poisson's ratios, and one dynamic bulk modulus. These data reveal possible causes of velocity anisotropy for these three rocks. Chelmsford Granite is a light gray, medium-grained quartz monzonite. In quarry terms, there are three sets of planes orthogonal to one another in this rock: "grain plane", "rift plane", and "hard-way plane". The grain plane is defined as the plane parallel to the cleavage planes of micas. The rift plane is defined as the plane parallel to the cracks. Peng (1970) found that most of the cleavage planes of micas are perpendicular to most of the cracks. Finally, the hard-way plane is defined as the plane perpendicular to both the grain plane and the rift plane. It is also the most 483