Report Summary

Abstract

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.