Method and apparatus for acoustic detection of a fluid leak behind a casing of a borehole

A method for detection of a leak behind a casing of a borehole, comprising

• investigating a portion of the borehole using a first investigation method to obtain a first result of investigation,
• investigating the portion of the borehole to obtain a second result of investigation using a method for acoustic detection of a leak behind a casing (23) of a borehole, the leak generating a discrete acoustic signal, the method for acoustic detection comprising:
• sampling an acoustic amplitude (AA) during a recording time period (24;64) at a determined position along the borehole,
• defining time intervals (26;66) inside of the recording time period (24),
• processing for each time interval (26) the measured acoustic amplitudes to obtain respectively a corresponding power-frequency spectrum (261),
• analysing a plurality of the power-frequency spectra to identify the discrete acoustic signal by detecting time and frequency dependant changes of power;
• comparing the first result of investigation with the second result of investigation to identify a correlation between the first result and the second result.

A method for repairing a leak behind a casing of a borehole, comprising:

• Detecting the leak using a method for acoustic detection of a leak behind a casing (23) of a borehole, the leak generating a discrete acoustic signal, the method comprising:
• i. sampling an acoustic amplitude (AA) during a recording time period (24;64) at a determined position along the borehole,
• ii. defining time intervals (26;66) inside of the recording time period (24);
• iii. processing for each time interval (26) the measured acoustic amplitudes to obtain respectively a corresponding power-frequency spectrum (261);
• iv. analysing a plurality of the power-frequency spectra to identify the discrete acoustic signal by detecting time and frequency dependant changes of power;
• Activating a repair process for repairing the leak.