Slim Litho-Density Module

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.

Features

• 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”)

Measurements

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

Applications

• Matrix Identification
• Formation fluid analysis
• Porosity

Operating Conditions

• Borehole type: 4” to 12” open hole