CASED HOLE GAMMA RAY
Gamma ray tools record naturally occurring gamma rays in the formations adjacent to the wellbore. This nuclear measurement indicates the radioactive content of the formations. Effective in any environment, gamma ray tools are the standard device
used for correlation of logs in cased and open holes
Applications
Depth determination
Depth correlation within the well and between wells
Lithology identification
Qualitative evaluation of shaliness
Qualitative evaluation of radioactive mineral deposits
Cased hole perforating depth control
Positioning for openhole sampling tools
CASED HOLE SPECTRAL GAMMA RAY
Spectral gamma ray tools provide insight into the mineral composition of formations. The total gamma ray spectra measured is resolved into the three most common components of naturally occurring radiation in sands and shales—potassium, thorium, and uranium (K, Th, and U, respectively). These data are used to distinguish important features of the clay or sand around the wellbore. The clay type can be determined, and sand can be identified as radioactive. The deposition of radioactive salts behind the casing by the movement of water can also be identified
The natural gamma ray spectrometry tool uses five-window spectroscopy to resolve the total gamma ray spectra into K, Th, and U curves. The standard gamma ray (SGR) and the gamma ray minus the uranium (CGR) component are also presented. The computed gamma ray or Th curve can be used to evaluate the clay content where radioactive minerals are present
Applications
Cation exchange capacity studies
Reservoir delineation
Detailed well-to-well correlation
Definition of facies and depositional environment
Igneous rock recognition
Recognition of other radioactive materials
Estimated uranium and potassium potentials
Lithologic analysis log input Nuclear