Communications – electrical: acoustic wave systems and devices – Seismic prospecting – Well logging
Patent
1995-05-10
1996-07-30
Lobo, Ian J.
Communications, electrical: acoustic wave systems and devices
Seismic prospecting
Well logging
367 25, 367 73, 364422, G01V 140
Patent
active
055418902
ABSTRACT:
A method of determining the acoustic propagation velocity of an earth formation penetrated by a wellbore by processing signals from an array acoustic wellbore logging tool. The tool includes a transmitter and a plurality of receivers axially spaced apart from the transmitter. The method includes the steps of combining signals generated by ones of the receivers in response to acoustic energy propagated through the wellbore from the transmitter, to generate a synthesized signal corresponding to another one of the receivers. The step of combining includes time shifting signals from the ones of the receivers by an amount corresponding to a predetermined velocity for each propagation mode and the axial distance between the ones of receivers and the other receiver. The synthesized signal is compared to the signal generated at the other receiver in response to the acoustic energy to determine a degree of correspondence between the synthesized signal and the received signal. The values of velocity for each propagation mode are varied, a signal is again synthesized and compared to the measured signal, and these steps are repeated until the degree of correspondence reaches a maximum. The values of velocity at which the degree of correspondence is a maximum are determined to be the acoustic propagation velocities of the earth formation for each of the different modes of propagation.
In a preferred embodiment of the invention, the step of comparing includes generating an object function of the difference between the synthesized signal and the received signal. The object function is minimized by the Levenberger-Marquardt algorithm to determine the values of velocity for each propagation mode.
REFERENCES:
patent: 210966 (1980-07-01), Ingram
patent: 4672588 (1987-06-01), Willen
patent: 4819214 (1989-04-01), Gutowski et al.
patent: 5197038 (1993-03-01), Chang et al.
Fagin Richard A.
Lobo Ian J.
Western Atlas International Inc.
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