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The litho-density tool combines a borehole- corrected bulk density measurement with a photoelectric lithology log (Pe). A radioactive source and detectors are mounted in an articulated skid maintained in contact with the borehole wall by a powered backup arm. The arm also doubles as a caliper measurement. The tool may be combined with compensated neutron, focused induction and sonic measurements in a classic ‘quad combo’ configuration.

Principle of measurement:

Gamma radiation from a 137Cs source is Compton scattered by the formation and detected by two scintillation detectors. The relative intensities of the radiation at each detector provide a measurement of formation bulk density. The photoelectric measurement is derived from the ratio of the gamma intensities in high and low energy windows at the short-spaced detector. The Pe measurement depends on the atomic number of the formation and is a good lithology indicator. Both density and Pe measurements are influenced by the borehole environment. These effects are minimised by corrections calculated by extensive Monte Carlo modelling and benchmarked to standards at the Callisto facility in Leicestershire, UK.


  • Drift eliminated by digital circuitry and active calibration loops based on internal reference sources
  • Well characterised tool response based on computer calculations
  • Tungsten carbide coated wear plate on skid can be replaced in the field
  • High-resolution measurement
  • Maximum data sampling rate is 1cm (0.4”)


  • Bulk density (rhoB)
  • Correction indicator (delta-rho)
  • Photoelectric effect (Pe)
  • Stabilisation loop indicator


  • Matrix
  • Identification
  • Formation fluid analysis
  • Porosity


Diameter: 63mm (2.5”)
Length: 3.23m (127”)
Weight: 60kg (132lb)
Max. temperature: 125°C
Max. pressure: 86MPa (12,500psi)
Density range: 1.1 to 2.95g/cc
Pe range: 1 to 10 Barns
Caliper range: 75mm (3”) – 400mm (12”)

Operating Conditions

Borehole type: 4” to 12” open hole

Sales Information

I003937 Litho-density probe
I013961 18.5GBq 137Cs source
I004126 Source holder
I004125 Source transport pig
I004123 Source handling tool set
I004129 Density/ Pe calibrator
I004131 Caliper calibrator

Download Litho-Density sheet


...Practical Innovation with Global Service & Support...

Robertson Geologging Ltd., 2017

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