Sidewall Density Probe
Sidewall Density/Guard Probe

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The Sidewall Density probe uses multiple detectors to provide an accurate borehole-compensated density measurement with excellent bed-boundary resolution. The Sidewall Density and Density/Guard Probe additionallyincludes a focussed LL3 resistivity measurement with a good vertical resolution and reasonable depth of penetration.

PRINCIPLE OF MEASUREMENT

Density
The probe contains a gamma source and two
high-sensitivity scintillation gamma detectors. The detectors are protected against direct radiation from the source or via the borehole by extensive heavy
metal shielding. The active windows of source and detector are maintained firmly in contact with the borehole walls by a motorised back-up arm that also provides a borehole caliper measurement. 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.

Resistivity
The probe includes a central measurement electrode with equipotential guard electrodes above and below. The measure current path is constrained to a thin disk and returns to cable armour above an insulated bridle.