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

摘要

An acoustic detection of a discrete acoustic signal allows to detect a leak behind a casing ( 23 ) of a borehole. An acoustic amplitude (AA) is sampled during a recording time period ( 24;64 ) at a determined position along the tube. Time intervals ( 26;66 ) are defined inside of the recording time period ( 24 ), and for each time interval ( 26 ) the measured acoustic amplitudes are processed to obtain respectively a corresponding power-frequency spectrum ( 261 ). A plurality of the power-frequency spectra are analyzed to identify the discrete acoustic signal by detecting time and frequency dependant changes of power. Preferably the processing involves a Fourier transform analysis. A power-frequency time plot is used to conveniently identify the discrete acoustic event.