Spectral Gamma Ray Tool


Fully characterized in the Houston API global reference standard, high resolution potassium, uranium and thorium measurements for reservoir analysis.


  • Quantitative measurement of actual radiation and separation into its three predominant components: potassium, uranium and thorium
  • Determination of clay and shale volumes
  • Clay typing
  • Heavy mineral identification
  • Input for complex lithology analysis
  • Differentiation between radioactive pay zones and shales
  • Identification of fractured and highly permeable zones where high uranium concentrations are present
  • Detailed well-to-well correlation

Features and Benefits

  • The highly sensitive NaI detector provides accurate spectral analysis of natural gamma ray energies.
  • Detailed spectrum determines Potassium, Uranium, and Thorium weight concentrations in the formation.

Tool Description

The Weatherford spectral gamma ray (SGR) tool provides superior clay type and volume analysis by measuring gamma ray energy from the naturally occurringradioactive elements potassium, uranium and thorium.

The SGR tool measures naturally occurring radioactive elements in formations to provide clay type and volume analysis. The tool contains a large scintillation crystal which provides higher detection efficiency and sensitivity. The result is a detailed spectrum of 256 discrete data channels.

Surface processing uses five energy windows to “strip” relative concentrations of potassium, uranium and thorium from the raw spectra.

The resulting log displays potassium content as a percentage of uranium and thorium contents in ppm. A total gamma curve equivalent to a regular natural gamma ray is also displayed, along with a uranium-free gamma ray curve. The tool is almost always run in combination with the Spectral Pe Density (SPeD) or advanced formation density (AFD) and Compensated Neutron Tool (CNT). These tools also can be combined with other services.