The 40GRP-1000 combination probe is ideal for slimline, one-pass, hydrogeological studies, lithology work, uranium exploration, and general borehole formation data. The totally digital probe combination measures 16, 64 inch (0.4, 1.6 meter) normal resistivity, single point resistance, self-potential, and natural gamma. It operates with the newest LoggerSuite digital logging system and software.

The 40GRP-1000 is a standalone tool. The normal resistivity measurements, single point resistance, and self-potential measurements are designed for surveying open (uncased) fluid-filled boreholes. Gamma measurements can be taken in any borehole environment.

40GRP Probe Image

  • N16 : 16” normal resistivity in ohm-m (short normal)
  • N64 : 64” normal resistivity in ohm-m (long normal)
  • SPR : single point resistance in ohms
  • SP : spontaneous potential in mV
  • GR : total gamma counts in cps/API


  • Bed boundary analysis
  • Facies changes
  • Quantitative geological formation properties
  • Identification of Hydrostratigraphic units
  • Aquifer thickness and Water quality
  • Hydrocarbon intervals, Ore body zones, In-situ Uranium assay
  • Fluid contaminant monitoring, Soil horizons, Grain size estimation

Operating Conditions

Natural Gamma can be used in any borehole conditions.

For all other measurements, the following conditions apply:

Borehole Fluid
[X] Water
[X] Mud
[_] Dry

[X] Uncased
[_] PVC Borehole
[_] Steel

[_] Required
[X] Not Necessary

Isolation Bridle
[X] Required
[_] Not Necessary

Features & Benefits

  • Can log five measurements in one pass, with one tool.
  • Wide range of applications- from hydrogeology to mining to hydrocarbons
  • Ultra slimline and easy one-person operation
  • Fully downhole digital, functions easily on longer wirelines

Specifications – Metric/English

Specification Metric Imperial
Diameter 43 mm 1.7″
Length 2.21 m 87″
Weight 8.8 Kg 19.5 lbs.
Max. Temp. 70ºC 158ºF
Max. Pressure 200 bar 2900 psi


Natural Gamma Sensor: Sodium Iodide Crystal
Gamma Range: 0 to 100,000 cps/API
Gamma Accuracy: 1%
Gamma Resolution: 0.02%

Resistivity Sensors: Stainless steel electrodes
Resistivity Range: 0 to 10,000 Ohm-m
Resistivity Accuracy: 1%
Resistivity Resolution: 0.02%

SPR Range: 0 to 10,000 Ohms
SPR Accuracy: 1%
SPR Resolution: 0.02%

SP Range: ± 1,500 mVDC
SP Accuracy: 1%
SP Resolution: 0.04%


Data Sheet for 40GRP Probe
User Guide

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