Communications – electrical: acoustic wave systems and devices – Testing – monitoring – or calibrating
Patent
1991-08-05
1992-09-08
Pihulic, Daniel T.
Communications, electrical: acoustic wave systems and devices
Testing, monitoring, or calibrating
367 35, H04B 1700
Patent
active
051464322
ABSTRACT:
Methods for characterizing acoustic transducers and using a characterized acoustic transducer for measuring cement impedance of a cased well are disclosed. The method for characterizing the acoustic transducer generally comprises: arranging the acoustic transducer a predetermined distance from a calibration target of known thickness; transmitting a pulse from the acoustic transducer through a known medium and toward the calibration target and measuring a return signal received therefrom; and fitting, via minimization, a return signal calculation generated by a model of the return signal which has a limited number of parameters, to the received return signal to determine a value for at least one of the parameters and thereby characterize the transducer. The preferred parameters for characterization are the transducer radius and stand-off, such that the transducer may be characterized as having an effective stand-off and an effective radius. The method for measuring cement impedance behind the casing in a well utilizes the method for characterizing the transducer, where the calibration target is preferbly of the same radius and thickness as the casing of the well. Then, downhole, a pulse is transmitted toward the casing in the well and the return signal is measured. Using the effective stand-off and effective radius previously determined as fixed values, the model of the return signal, which utilizes reflective coefficients which, inter alia, are a function of the cement impedance, is fit to the actual return signal to determine an indication of the cement impedance.
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patent: 4970695 (1990-11-01), Huau
"Transducer effects in acoustic Scattering measurements" by Johnson & Devaney, Appl. Phys. Lett. vol. 41, No. 7, Oct. 1, 1982, pp. 622-624.
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"Mathematical model for internal ultrasonic inspection of cylindrially layered structures" by Randel et al., J. Acoustic Soc. Am 83 Apr. 1988, pp. 1295-1305.
Ayter Sevig
Kimball Christopher V.
Foodman Marc D.
Gordon David P.
Pihulic Daniel T.
Schlumberger Technology Corporation
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