Report Summary

Abstract

This report contains the results ot work completed during the fifth year of the Full Waveform Acoustic Logging Consortium in the Earth Resources Laboratory at M.l.T. During this past year, the emphasis in our research has continued in the direction of a more balanced treatment of all aspects of the acoustic logging problem, namely, theory, data processing, and interpretation. The aim is faster and more accurate determination of formation properties from the full waveform acoustic logs under. a variety of conditions one might encounter in the field. In situ permeability, in both porous and fractured formations, remains the focus of our research efforts. In this report we have a number of papers dealing with the subject, from theoretical papers studying wave propagation in a radially layered porous formation and shear wave logging in a porous medium, to a progress report on finite difference modelling of wave propagation in a porous material, and ultrasonic modelling of the effects of fractures on full waveform logs. We have also examined the correlation between permeabilities obtained from full waveform logs and those measured in core samples. A paper on the depth of investigation of different methods of in situ fracture permeability determination is also included in the report. Data processing received more attention in the past year. We have continued to work on some of the projects we had started last year, namely, the inversion of the P wavetrain for V, and Qp in a slow formation, and the determination of formation velocities behind (poorly bonded) casing using velocity analysis. In addition, we have initiated efforts in array processing of full waveform logging data using the extended Prony's method.

This method is very promising for the accurate determination of formation guided (both pseudo-Rayleigh and Stoneley) wave dispersion and attenuation. In an effort to further study how the borehole affects the determination of formation properties, we have studied the effect of the viscosity of the borehole fluid on full waveform logs. We have also made laboratory measurements of the quality factor of a drilling mud. Lastly, but not least, we have initiated efforts of incorporating expert system approaches in the interpretation of full waveform logs. Two papers, one on the correlation of waveforms for better velocity determination, and the other on well-to-well log correlation, represent our initial efforts in this area. The following is a summary of the papers in this report.