Correlation of longitudinal velocity variation with rock fabric

Abstract

Comparisons of longitudinal (compressional) wave velocity with structural subfabrics have been made for Yule marble, Newberry Crater pumice, and Salisbury granite. Velocities were (1) measured omnidirectionally in spherical specimens by an ultrasonic pulse technique and (2) plotted and contoured on equal area nets. These contour patterns show velocity anisotropy that can be interpreted in terms of elastic symmetry. Microstructural subfabrics were determined from oriented thin sections of the specimens. Subfabrics were then displayed on equal area nets for comparison of their symmetries with those of the longitudinal wave velocities. The two structural subfabric elements selected for comparison were crystallographic orientation of constituent anisotropic minerals and shape and orientation of pores or cracks. The longitudinal velocity symmetry in Yule marble appears to be axial, whereas in both Newberry Crater pumice and Salisbury granite the pattern is orthorhombic. The pattern of longitudinal velocity anisotropy is associated with preferred orientation of calcite optic axes in Yule marble, preferred orientation of elongate vesicles in the Newberry Crater pumice, and preferred orientation of microfractures in quartz in the Salisbury granite. A prospectus given suggests that the petrophysical technique described can be used to determine elastic symmetry, orient rock to inherent elastic symmetry axes, indicate sample homogeneity, and supplement conventional petrofabric techniques.

Directional Variation of Elastic Wave Velocities in Oriented Clay

“…Directional variation of velocity in rocks has been studied by Thill, Willard and Bur (1969), who compared directional velocity distributions with rock fabric as determined from optical studies of thin sections, in marble, granite, and pumice specimens. The greatest degree of sonic anisotropy was found in pumice, where it was associated with elongation of vesicles with preferential orientation, and was found to have orthorhombic symmetry.…”

Comparison between permeability anisotropy and elasticity anisotropy of reservoir rocks

“…The method is based on the measurement of ultrasonic velocities in a large number of directions on rock samples. The idea is not new (e.g., Pros and Babuska, 1967;Thill et al, 1969). The new experimental aspect here is that not only the confining pressure (as in Pros and Podrouskova, 1974), but also the pore pressure are independently controlled.…”

Evaluation for Rock Cleavage Using Distribution of Microcrack Lengths and Spacings (1)

“…This type of correlation analysis is useful for evaluating the relative strength of rock cleavage and discriminating three quarrying planes. (Park, 2007) (Douglass and Voight, 1969;Thill et al, 1969;Peng and Johnson, 1972;Thill et al, 1973;Plumb et al, 1984) 그리고 국내의 연구사례 (Jang and Oh, 2001;Park et al, 2001Park et al, , 2004Park, 2007Park, , 2011Park, , 2015aPark, , 2015b)에서는 석영 및 장 석내 미세균열을 강조하고 있으며, 상대적인 분리성, 즉 리프트 > 그레인 > 하드웨이를 제시하고 있다. 이외 국내의 연구 사례 (Jang et al, 1998;Lee et al, 1999;Seo and Jeong, 1999;Seo et al, 2002;Park and Seo, 2003;Park, 2005;Chae and Seo, 2011;Kang et al, 2014) …”