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Title: Microcrack-induced elastic wave anisotropy of brittle rocks

Abstract

The failure of brittle rocks during compression is preceded by the formation, growth, and coalescence of microcracks. Elastic wave velocities are reduced in the presence of open microcracks and fractures and may therefore be used to monitor the progressive damage of the rock. In general, these microcracks are not randomly oriented, and the rock displays an elastic anisotropy. The elastic anisotropy due to cracks can be expressed in terms of a second-rank and fourth-rank crack density tensor. For open cracks the contribution of the fourth-rank crack density tensor to the elastic wave velocities is small. These results are compared with recent measurements of the ultrasonic compressional and shear wave velocities for propagation parallel and perpendicular to an increasing axial stress applied at constant confining stress to Berea sandstone. Inversion of the velocity measurements indicates that the microcracks propagate parallel to the maximum compressive stress, in agreement with current rock mechanics theory. A reasonable fit to the data is obtained using only the second-rank crack density tensor even though, at high confining stress, the cracks are expected to be in partial contact along their length. This is consistent with the model of elastic wave propagation in a medium containing partially contactingmore » fractures published by White. However, measurements of off-axis wave velocities are required to fully quantify the contribution of the fourth-rank crack density tensor. 28 refs., 10 figs.« less

Authors:
 [1];  [2]
  1. Schlumberger Cambridge Research, Cambridge (United Kingdom)
  2. Tufts Univ., Medford, MA (United States)
Publication Date:
OSTI Identifier:
181969
Resource Type:
Journal Article
Journal Name:
Journal of Geophysical Research
Additional Journal Information:
Journal Volume: 100; Journal Issue: B3; Other Information: PBD: 10 Mar 1995
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; 15 GEOTHERMAL ENERGY; 02 PETROLEUM; 03 NATURAL GAS; SANDSTONES; FRACTURES; ELASTICITY; ULTRASONIC WAVES; ANISOTROPY; WAVE PROPAGATION; BRITTLENESS

Citation Formats

Sayers, C M, and Kachanov, M. Microcrack-induced elastic wave anisotropy of brittle rocks. United States: N. p., 1995. Web. doi:10.1029/94JB03134.
Sayers, C M, & Kachanov, M. Microcrack-induced elastic wave anisotropy of brittle rocks. United States. doi:10.1029/94JB03134.
Sayers, C M, and Kachanov, M. Fri . "Microcrack-induced elastic wave anisotropy of brittle rocks". United States. doi:10.1029/94JB03134.
@article{osti_181969,
title = {Microcrack-induced elastic wave anisotropy of brittle rocks},
author = {Sayers, C M and Kachanov, M},
abstractNote = {The failure of brittle rocks during compression is preceded by the formation, growth, and coalescence of microcracks. Elastic wave velocities are reduced in the presence of open microcracks and fractures and may therefore be used to monitor the progressive damage of the rock. In general, these microcracks are not randomly oriented, and the rock displays an elastic anisotropy. The elastic anisotropy due to cracks can be expressed in terms of a second-rank and fourth-rank crack density tensor. For open cracks the contribution of the fourth-rank crack density tensor to the elastic wave velocities is small. These results are compared with recent measurements of the ultrasonic compressional and shear wave velocities for propagation parallel and perpendicular to an increasing axial stress applied at constant confining stress to Berea sandstone. Inversion of the velocity measurements indicates that the microcracks propagate parallel to the maximum compressive stress, in agreement with current rock mechanics theory. A reasonable fit to the data is obtained using only the second-rank crack density tensor even though, at high confining stress, the cracks are expected to be in partial contact along their length. This is consistent with the model of elastic wave propagation in a medium containing partially contacting fractures published by White. However, measurements of off-axis wave velocities are required to fully quantify the contribution of the fourth-rank crack density tensor. 28 refs., 10 figs.},
doi = {10.1029/94JB03134},
journal = {Journal of Geophysical Research},
number = B3,
volume = 100,
place = {United States},
year = {1995},
month = {3}
}