Mobil Oil Corporation

Denis P Schmitt

Charles L Dennis

Keh Pann

Robert G Keys

Will K Lenhardt

John A Nieto

A method for eliminating sinusoidal noise without affecting the response of the formation means that the actual formation responses of the logging tools are recovered, and the logs can be used quantitatively. Removal of sinusoidal noise from a log is accomplished in three steps. First, the log is reduced to a zero-mean, stationary series. Second, the wavenumber of the sinusoidal noise is identified by its peak in the Fourier amplitude spectrum. And third, the noise is removed by applying a zero-phase notch filter. In order to preserve the quantitative data integrity, the low wavenumber trend is kept. Preserving the quantitative data integrity is accomplished by approximating the log with a least-squares cubic spline which retains the overall log character, ignoring the sinusoidal noise. A zero mean stationary series is formed by subtracting the least-squares cubic spline from the data. The remaining steps, Fourier analysis and filtering are performed on the difference series. Recombining the filtered series with the spline restores the log data without the sinusoidal noise.

Method for removing borehole rugosity noise from well log data

A borehole logging tool having a dipole acoustic energy source and at least one spaced-apart dipole acoustic energy receiver is lowered into a deviated borehole. A motor rotates the source and receiver about the axis of the borehole tool. A first signal is produced representing source and receiver rotational position relative to rotational position of the borehole tool. A second signal is produced representing rotational position of the borehole tool relative to a vertical direction. A comparator produces a third signal of the difference between the first and second signals as a representation of source and receiver rotational position relative to the vertical direction. The motor rotates so as to minimize such third signal, thereby rotating the focus of the source and receiver in a direction perpendicular to the eccentricity of the borehole tool in the deviated borehole.

Apparatus for rotating a transducer assembly of a borehole logging tool

A borehole logging tool having a dipole acoustic energy source and at least one spaced-apart dipole acoustic energy receiver is lowered into a deviated borehole. A motor rotates the source and receiver about the axis of the borehole tool. A first signal is produced representing source and receiver rotational position relative to a vertical direction. A second signal is produced representing a fixed reference level. A comparator produces a third signal of the difference between the first and second signals. The motor rotates so as to minimize such third signal, thereby maintaining the focus of the source and receiver in a horizontal direction that is perpendicular to the direction of eccentricity of the borehole tool with respect to the borehole axis.

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Richardson, TX, United States of America

Denis P Schmitt