Anisotropy of elastic moduli, P-wave velocities, and thermal conductivities of Asan Gneiss, Boryeong Shale, and Yeoncheon Schist in Korea

Abstract

This paper presents the anisotropic characteristics of the elastic moduli, P-wave velocities, and thermal conductivities of three types of anisotropic rocks, i.e., Asan gneiss, Boryeong shale, and Yeoncheon schist, occurring in Korea. The experiments were conducted on rock samples that show clear evidence of transverse isotropy. Cylindrical core samples with different anisotropy angles were prepared by coring at 15-degree intervals from the transversely isotropic plane using the laboratory directional coring system established for this study. Elastic moduli, P-wave velocities, and thermal conductivities were determined along the sample axis for different anisotropy angles. The anisotropy ratio is defined as the ratio of the properties parallel to the transversely isotropic plane to those perpendicular to the plane, and the anisotropy ratios for the thermal conductivities (K(90°)/K(0°)) of Asan gneiss, Boryeong shale, and Yeoncheon schist were 1.4, 2.1, and 2.5, respectively. The P-wave velocity anisotropy ratios (VP(90°)/VP(0°)) for Asan gneiss, Boryeong shale, and Yeoncheon schist were 1.2, 1.5, and 2.3, respectively. The elastic moduli, P-wave velocities, and thermal conductivities that were obtained were compared with theoretical predictions by mean prediction error (MPE). The correlations between the measured properties were evidently correlated with some minor scatter in the data. The degree of anisotropy measured in this study suggests that ignoring anisotropy in rock properties may mislead to erroneous results. The application of tensorial transformation evaluations revealed that the three types of rocks chosen for this study can be modeled effectively by a transversely isotropic model.