EMAT acoustic signal measurement using modulated Gaussian wavelet and Hilbert demodulation

摘要

Casing signals generated by an EMAT in a borehole are processed using at least two orthogonal band-limited filters. The band-limited filters may include Gaussian or Cauchy Wavelet filters. By using the Hilbert transform, an envelope of the filtered signals is determined and amplitudes and arrival times of individual arrivals are estimated. These can be used to estimate casing and cement properties.

主权项

1. A method of characterizing a casing installed in a borehole in an earth formation, the method comprising:
activating a transducer at at least one azimuthal orientation in the borehole and generating an acoustic pulse; receiving a signal comprising a plurality of events resulting from the generation of the acoustic pulse; bandpassing the received signal using two modulated filters in a time domain, the two modulated filters being orthogonal to one another, and providing a bandpassed signal; estimating an envelope of the bandpassed signal; and estimating from the envelope of the bandpassed signal an arrival time of each of the plurality of events, the arrival times being characteristic of a property of at least one of: (i) the casing, and (ii) a cement in an annulus between the casing and the formation.