Determination of near wellbore properties using natural gamma rays

A system comprising:

• a tool having a detector to detect gamma rays, the tool operable downhole in a well;
• and
• a processor arranged to
• determine deviation of energy spectra of gamma rays detected in downhole operation of the tool in each selected energy window of a set of selected energy windows with respect to a reference energy spectra of the respective selected energy window, and
• determine one or more properties of one or more regions around the tool, when the tool is disposed downhole in the well, from the deviation of the energy spectra, the regions being between the tool and a source of the detected gamma rays in a formation around the well,
• wherein determination of one or more properties includes a determination of at least one of a borehole fluid density and an annular space density.

A machine-readable storage device having instructions stored thereon, which, when performed by a machine, cause the machine to perform operations, the operations comprising:

• determining, via a processor, deviation of energy spectra of gamma rays in each selected energy window of a set of selected energy windows with respect to a reference energy spectra of the respective selected energy window, wherein the gamma rays are detected in a detector of a tool disposed downhole in a well;
• and
• determining, via the processor, one or more properties of one or more regions around the tool from the deviation of the energy spectra, the regions being between the tool and a source of the detected gamma rays in a formation around the well,
• wherein determining one or more properties includes determining at least one of a borehole fluid density and an annular space density.