Communications – electrical: acoustic wave systems and devices – Seismic prospecting – Well logging
Patent
1995-08-11
1997-08-26
Moskowitz, Nelson
Communications, electrical: acoustic wave systems and devices
Seismic prospecting
Well logging
367 26, 367 73, 364421, G01V 140, G01V 128
Patent
active
056616961
ABSTRACT:
Methods and apparatus for generating an error bar (variance) log for a formation parameter are disclosed. According to the method, acoustic waveforms are detected at a plurality (M) of detectors which are a function of a source signal which has interacted with the formation and noise, and the detected waveforms are sampled and processed in order to obtain a semblance or a normalized mean square error. Using the semblance or the NMSE which is related to the semblance, a signal to noise ratio 2E/N.sub.0 can be found by recognizing that the semblance function has a non-central beta distribution whose mean is a function of the signal to noise ratio 2E/N.sub.0, the time-bandwidth product N, and M. The signal to noise ratio is then used to find the Cramer-Rao lower bound which is taken as an estimate of the variance. An error bar log is formed by repeating these steps at a plurality of locations along the borehole. The method of the invention can be used in conjunction with both attenuating and non-attenuating waves. The apparatus of the invention relates closely to the method.
REFERENCES:
patent: 4543648 (1985-09-01), Hsu
patent: 4698793 (1987-10-01), Wu
patent: 4839869 (1989-06-01), Corcoran
patent: 4888740 (1989-12-01), Brie et al.
patent: 5278804 (1994-01-01), Kimball
Kimball Christopher K.
Scheibner David J.
Gordon David P.
Jeffery Brigitte L.
Moskowitz Nelson
Schlumberger Technology Corporation
Smith Keith G. W.
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