Determining impedance of material behind a casing in a borehole
Patent
·
OSTI ID:7090693
This patent describes a method of calculating an impedance signal related to an acoustic impedance of material behind a section of casing in a borehole, the borehole traversing subsurface earth formations, the method analyzing a return waveform obtained from an acoustic investigation of the section of casing with an acoustic excitation pulse directed thereto, the bandwidth of the pulse selected to stimulate a thickness resonance of the casing, the return waveform including a reverberation segment and an initial reflection segment. It comprises: determining the frequency of the thickness resonance from the return waveform, determining a time reference indicative of the time of arrival of the return waveform, and filtering the reverberation segment in a predetermined band about the determined thickness resonance frequency, the bandwidth of the predetermined band based on the determined frequency and substantially excluding other thickness resonances; time windowing a portion of the filtered reverberation segment based on the time reference and the determined frequency; and calculating an integrated, amplitude-related measure of the window reverberation segment to produce an impedance signal.
- Assignee:
- Schlumberger Technology Corp., New York, NY (USA)
- Patent Number(s):
- US 4928269; A
- Application Number:
- PPN: US 7-368065A
- OSTI ID:
- 7090693
- Country of Publication:
- United States
- Language:
- English
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