Abstract

From calculations of the intensity of unscattered gamma rays inside cylindrical self-absorbing sources, curves have been developed that aid in the application of gamma-ray spectrometric techniques to borehole logging. Specifically, the curves provide factors which can be used to normalize spectral data to any standard set of borehole and formation conditions used for calibration. Taken into account are the effects of borehole diameter, mud density, casing and cement thickness, bed thickness, and detector eccentricity. Illustrative examples of applications of these curves depict the solutions to a variety of specific problems as well as methods for obtaining additional curves. Curves showing the portion of the log response due to gamma rays originating within specific zones of the formation provide an evaluation of the depth of investigation of the gamma-ray spectral log.

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