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Effects of Formation Boundaries on Full Waveform Acoustic Logs
Benoit J. Paternoster
Submitted
to the Department of Earth, Atmospheric, and Planetary Sciences in May 1985
in partial fulfillment of the requirements for the degree of Doctor of Philosophy
Abstract
The first
part of this thesis is concerned with reflection and transmission of acoustic
waves at a layer boundaries in boreholes. The scattering effects produce events
that are oblique with respect to the main wavefield on iso-offset sections.
Such events have been recorded by the full waveform acoustic logging tool
EVA. Wave type conversions are also currently observed. Ray modeling reveals
the sensitivity of the apparent velocity of such events to the dip angle of
the interface. Two sections of real data are presented and interpreted: dip
angles of the interfaces are estimated.
In thinly bedded formations, the exact location and amplitude of velocity
contrasts across boundaries are sometimes difficult to estimate. These features
are greatly affected by the minimum spacing between the probe receivers. Improvements
in spatial resolution can be made, however, when the spatial sampling of the
formation is less than the tool minimum spacing. The second part of this thesis
proposes a recursive least squares inversion of travel times for the formation
slowness based on the Kalman filter. This formulation emphasizes the noise
content of the data as a factor limiting resolution. A data adaptive inversion
scheme is also developed in order to sharpen large contrasts in formation
properties. Results from synthetic data as well as real data processing are
presented.
