VSP Detection of Fracture-Induced Velocity Anisotropy

David H. Johnston

A multiple S-wave polarization VSP survey using gyroscopically oriented three-component downhole recording documented azimuthal anisotropy associated with the preferential orientation of fractures within the Austin Chalk. The anisotropy is manifest in a significant velocity contrast between S-waves polarized parallel to and perpendicular to the dominant fracture orientation as determined by bore-hole televiewer data. In addition, as discussed by Becker and Perelberg in another paper, for S-waves polarized 45° to the principal axes of symmetry, particle motions recorded within the Austin exhibit birefringence or splitting.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.