Abstract

A method and apparatus for measuring an earth formation characteristic from inside a borehole penetrating earth formations is described. A tool carrying a sonic transmitter and an array of receivers is moved along the borehole and waveform signals from the receiver array are generated from repetetive operations of the transmitter. Sub-arrays of particularly related waveform signals relevant to a selected depth interval that is less in length than the aperture of the array are identified. Each sub-array of signals is then converted to a domain of signals composed of values of a coherence as a function of a range of values of a characteristic such as slowness. The converted signals are then combined so as to provide combined coherence values as a function of different values of the characteristic. One or several peaks of the combined coherence values are detected and determine the value of the characteristic for the selected depth interval. Similar processing is continued for other depth intervals. Independent measurements of the characteristic can be made with both receiver section and transmitter section processing and a borehole compensation technique is described. A fast processing technique for processing data of many sub-array waveforms is described.

Other References

• Article entitled "A New Approach to Sonic Loggin and Other Acoustic Measurements", by Kokesh et al., Published in the Mar. 1965 Issue of the Journal of Petroleum Technology, pp. 282-286
• Article entitled: "Data Adaptive Spectral Analysis Methods", by R. T. Lacoss, Published in Geophysics, vol. 36, No. 4, (Aug. 1971), pp. 661-675, 7 FIGS., 3 Tables