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Abstract:
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This report contains the results of work completed during the sixth year of the Full
Waveform Acoustic Logging Consortium in the Earth Resources Laboratory at M.LT.
Over the last six years, our work have evolved from simply modelling an open borehole
in an isotropy, elastic formation to the study of logging under more complicated, realistic conditions, especially those that may be encounted in production and development environments.
In the past year, we have modelled elastic wave propagation in a transversely
isotropic formation, in a formation where the borehole is irregular in radius, across an
open fracture, and in a transversely isotropic porous formation, where the horizontal
and vertical permeabilities are different. All of these situations are rather common in
the field. It is important for us to understand how these complications mayor may
not affected our interpretation of the full waveform acoustic logs, and how large an
error we are likely to make if our interpretation is based on a isotropy, elastic model
of the formation. Just as importantly, we need to learn to identify these situations in
the field, so that we can make the appropriate corrections to our interpretation.
In data analysis, we have refined the Extended Prony's Method to calculate the
dispersion and attenuation of the guided waves in the borehole, and have applied
the technique to both laboratory and field data with success. We have also studied
the sensistivity of the guided waves to a transversely anisotropic formation. These
sensistivities are critical in the inversion of the dispersion and attenuation obtained
by the Extended Prony's Method for the actual elastic and anelastic properties of the
formation.
In a continuation of last year's work, we have studied the attenuation of solid particles
in a viscous fluid, applicable to the study of both drilling muds and unconsolidated
sands.
We have studied the diffraction of a cylindrical transducer and its effect on the
measurement of attenuation in laboratory experiments using the spectral ratio technique.
We are also continuing in our effort of scale model experiments to mimic field
situations which are not readily modelled by analytic or numerical methods.
A field study and comparison of velocities from core measurement, borehole compensated
sonic log, full waveform acoustic log, and VSP in the Salton Sea Scientific
Drilling Program is included in this report. Also included is an extended abstract on an
effort to map fractures in the Canadian Shield using borehole geophysical techniques.
The following is a summary of the papers in this report. |
