Communications – electrical: acoustic wave systems and devices – Seismic prospecting – Well logging
Patent
1992-10-26
1994-01-11
Lobo, Ian J.
Communications, electrical: acoustic wave systems and devices
Seismic prospecting
Well logging
367 31, 367 34, G01V 140
Patent
active
052788059
ABSTRACT:
Methods and related apparatus for conducting shear slowness logging are set forth. The methods broadly comprise: detecting dispersive waves such as flexural or Stoneley waves; Fourier transforming the received signals; backpropagating the Fourier transformed signals according to equations using different dispersion curves; stacking the backpropagated signals; and finding semblances in order to choose the dispersion curve of maximum semblance and thereby identifying the shear slowness of the formation. Formation shear slowness may be plotted over borehole depth. Different embodiments are set forth. In one preferred embodiment (QDSTC), prior to Fourier transforming, the signals are stacked according to a previous estimation of slowness (S.sub.0), and are windowed for maximum energy. The reduced set of data in the window are then extracted for Fourier transformation, and prior to backpropagation, multiplied by S.sub.0 to reset them for backpropagation and stacking. In another preferred embodiment (DSTC), after the signals are backpropagated, the backpropagated signals are inverse fourier transformed and windowed. In DSTC, semblance values may be plotted as a function of slowness and time. Regardless of embodiment, the methods of the invention account for non-dispersive waves by using dispersion curves of constant value during backpropagation.
REFERENCES:
patent: 4594691 (1986-06-01), Kimball et al.
patent: 5077697 (1991-12-01), Chang
"Aquisition and Analysis of Sonic Waveforms from a Borehole and Dipole Source . . . " by Harrison et al. SPE 20557, pp. 267-282 Society of Petroleum Engineers, Inc. 1990.
"Semblance Processing of Borehole Acoustic Array Data" by Kimball et al. Geophysis, vol. 49, No. 3, Mar. 1984, pp. 274-281.
"Inversion of P and SV Waves from Multicomponent Offset Vertical Seismic Profiles" by Esmersoy Geophysics, vol. 55, No. 1, Jan. 1990, pp. 35-50.
Gordon David P.
Lobo Ian J.
Pojunas Leonard W.
Schlumberger Technology Corporation
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