Estimation Of Nonorthogonal Shear Wave Polarizations And Shear Wave Velocities From Four-Component Dipole Logs
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1996.2 Nolte.pdf
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Author(s)
Nolte, Bertram
Cheng, Arthur C. H.
Date Issued
1996
Publisher
Massachusetts Institute of Technology. Earth Resources Laboratory
Series/Report no.
Earth Resources Laboratory Industry Consortia Annual Report;1996-02
Abstract
Polarizations of split shear waves and flexural borehole waves are most commonly estimated from four-component data using the rotation technique of Alford (1986). This
method is limited to the case of the two polarizations being orthogonal to each other.
We present a method that is able to handle the case of nonorthogonally polarized waves
and, moreover, is computationally more efficient than Alford's technique. Our method
is based on the eigenvalue decomposition of an asymmetric matrix and a least-squares
minimization of its off-diagonal components. In the case of orthogonally polarized waves,
our method will yield exactly the same results as the Alford rotation. We apply our
method to a cross-dipole shear-wave logging data set from the Powder River Basin in
Wyoming and find that independently rotated source-receiver sets are very consistent
with each other in anisotropic sections. After the rotation we compare two methods
for estimating the phase velocities of fast and slow waves-a semblance method and
homomorphic processing (Ellefsen et al., 1993). We find homomorphic processing to be
more reliable due to the dispersive nature of flexural waves.
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