Massachusetts Institute of Technology. Earth Resources Laboratory
Abstract
Two modes of flexural waves can be generated by a dipole source in an anisotropic
borehole. Their velocities are related to those of the fast and slow shear waves in
the formation. The particle motions and the polarization diagrams of the fast and
slow flexural waves are measured in borehole models made of phenolite materials with
transverse isotropy or orthorhombic anisotropy. The experimental results show that
the particle motion of the fast flexural wave is linear and in the same direction as that
of the fast shear wave in the formation. The polarization direction of the fast flexural
wave coincides with that of the fast shear wave and is independent ofthe direction of the
dipole source. The particle motion of the slow flexural wave is nonlinear and elliptic. Its
polarization direction and variation are dependent on the anisotropic material and the
source direction. This means that the slow flexural wave is a more complicated wave
mode rather than the simple mode where the particle motion generated by a dipole
source is in the direction of the slow shear wave. The polarization characteristics of
the fast flexural wave can be applied to determine the principal axis of an anisotropic
formation by in-line and cross-line logging data.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumUnited States. Dept. of Energy (Contract DE-FG02-86ER13636
