Method and apparatus for spectral noise logging

A method for producing a spectral noise log of a borehole, said method comprising:

• recording two or more power-frequency spectrum data sets at each of two or more stationary positions within a borehole;
• detecting an acoustic noise within a first frequency range;
• detecting an acoustic noise within a second frequency range, said second frequency range comprising lower frequencies than said first frequency range;
• and
• processing said two or more power-frequency spectrum data sets recorded at each of said two or more stationary positions so as to assign a single power frequency spectrum per each of said two or more stationary positions.

A spectral noise logging (SNL) tool, said tool comprising:

• an acoustic detector;
• a first frequency channel comprising a first gain stage arranged to amplify a first component of an electrical output signal generated by said acoustic detector;
• a second frequency channel comprising a second gain stage arranged to amplify and filter a second component of said electrical output signal generated by said acoustic detector;
• an analogue to digital convertor capable of digitizing an amplified output from said first gain stage;
• a computer processing unit (CPU) capable of processing a digitized output from said analogue to digital convertor and generating a power frequency spectrum data set;
• and
• an internal memory capable of storing said power frequency spectrum data set.