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Density Gamma Probe (Trisonde)

The trisonde is a convenient alternative to the standard RG sidewall density probe whenever borehole diameter is restricted and qualitative density measurements are sufficient. One common application is logging through drill pipe when unstable borehole conditions prevent use of unprotected nuclear probes. The logging probe is unfocussed and indicates the average density of material surrounding the borehole.

Principles of Measurement

The sidewall density probe contains a gamma source and two high-sensitivity scintillation gamma detectors. Gamma radiation from the source is backscattered by the formation (Compton effect) and reaches the two detectors where the relative count-rates provide a measure of formation bulk density.


  • Long-spacing detector (LSD) for deep penetration and immunity from borehole effects.
  • High-resolution detector (SSD) for accurate bed-boundary detection.
  • Bed-resolution detector (BRD) for shallow penetration and borehole effects.


  • Long-spacing density (LSD)
  • High-resolution density (SSD)
  • Bed Resolution density (BRD)
  • Temperature
  • Natural gamma



Lithology, Bulk density variations, Correlation with other logs, Bed thickness and boundary location, Borehole inclination and true vertical depth.


Optional 110/220VAC power supply (also powers SMART portable wireline winch). Detection of weathered or fractured zones, Ground compaction studies.


Location of aquifer and aquitard, Detection of cavities and missing cement around casing.

Operating Conditions

Borehole type: All