Method of analyzing waveforms

A method of analyzing acoustic waveforms obtained in a cased well, comprising:

• a) obtaining a series of waveforms from sequential geometric positions in the well;
• b) identifying and removing echoes from a first interface in each waveform;
• c) determining a part of each remaining waveform due to casing resonance and analyzing each waveform to determine a parameter;
• d) sorting waveforms into bins, each bin including waveforms for which values of the parameter are substantially the same;
• e) determining a mean waveform for each bin;
• f) scaling said mean waveforms to determine scaled mean waveforms for each bin;
• g) for each bin, subtracting the scaled mean waveform from each waveform in the bin;
• and
• h) ordering the waveforms in accordance with the sequential geometric positions from which they were originally obtained and identifying echoes resulting from a third interface.

A method of analyzing acoustic waveforms obtained in a well having a casing located therein and surrounded by cement, comprising:

• a) obtaining a series of waveforms from sequential geometric positions in the well;
• b) normalizing and shifting the waveforms to align echoes resulting from a first interface;
• c) determining a parameter related to casing thickness for each waveform and sorting waveforms into first bins, each first bin including waveforms for which values of the parameter are substantially the same;
• d) determining a mean waveform for each first bin and subtracting a scaled version of the mean waveform from each waveform in the corresponding first bins so as to remove echoes resulting from first and second interfaces and leave echoes resulting from a third interface;
• e) shifting the waveforms to align third interface echoes;
• f) sorting the shifted waveforms according to values of the parameter related to thickness and dividing the sorted waveforms into second bins;
• g) determining a mean waveform for each second bin and subtracting a shifted and scaled version of this mean waveform from the corresponding waveform in the series so as to rename the third interface echo and provide a corrected series;
• and
• h) analyzing the corrected series to determine a parameter related to the cement around the casing.

A method of analyzing waveforms which contain components arising from at least first and second substantially uncorrelated features, the method comprising:

• (a) determining a value of at least one parameter from each waveform;
• (b) determining a mean waveform for waveforms having similar values of the at least one parameter;
• (c) subtracting the mean waveform from each waveform having the similar value of the at least one parameter;
• and
• (d) analyzing the waveforms to determine the second feature.

A method of analyzing acoustic waveforms obtained in a cased well, comprising:

• (a) obtaining a series of waveforms from sequential geometric positions in the well;
• (b) identifying and removing echoes resulting from a first interface in each waveform;
• (c) determining a part of each remaining waveform due to casing resonance and analyzing each waveform to determine a parameter;
• (d) sorting waveforms into bins, each bin including waveforms for which values of the parameter are substantially the same;
• (e) determining a mean waveform for each bin and subtracting said mean waveform from each waveform in the bin;
• and
• (f) ordering the waveforms in accordance with the sequential geometric positions from which they were originally obtained and identifying echoes resulting from a third interface.

A method of analyzing acoustic waveforms obtained in a well having a casing located therein and surrounded by cement, comprising:

• (a) obtaining a series of waveforms from sequential geometric positions in the well;
• (b) normalizing and shifting the waveforms to align echoes resulting from a first interface;
• (c) determining a parameter related to casing thickness for each waveform and sorting the waveforms into first bins, each first bin including waveforms for which values of the parameter are substantially the same;
• (d) determining a mean waveform for each first bin and subtracting said mean waveform from each waveform in the corresponding first bins so as to remove echoes resulting from first and second interfaces and leave echoes resulting from third a third interface;
• (e) shifting the waveforms to align third interface echoes:
• (f) sorting the shifted waveforms according to values of the parameter related to thickness and dividing the sorted waveforms into second bins;
• (g) determining a mean waveform for each second bin and subtracting a shifted version of this mean waveform from the corresponding waveform in the series so as to rename the third interface echo and provide a corrected series;
• and
• (h) analyzing the corrected series to determine a parameter related to the cement surrounding the casing.