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.
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.
|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”)|
Borehole type: 4” to 12” open hole
|I013961||18.5GBq 137Cs source|
|I004125||Source transport pig|
|I004123||Source handling tool set|
|I004129||Density/ Pe calibrator|
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Robertson Geologging Ltd., 2017
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