The QL40-FTC, QL40-FTC-I, and 40FTC probes provide borehole temperature and fluid conductivity measurements.  The standard temperature log, based on a thermister, is designed to provide a measure of the ambient geothermal gradient and is helpful to detect anomalies caused by events such as fluid flow into the borehole.

The borehole fluid conductivity is directly proportional to the concentration of dissolved minerals. It is generally used in hydrogeology to determine the concentration of dissolved ions in the aquifers and to locate the fluid flows occurring in the borehole, especially if some time has passed and the temperature features have dissipated. It is important to differentiate between fluid inflow anomalies and formation conductivity anomalies identified on the temperature logs.


The QL40-FTC can be combined with other logging tools of the QL (Quick Link) product line as a bottom-sub only sonde or used inline as the QL40-FTC-I. This tool can also be operated as a standalone, non-stackable tool known as the 40FTC.


  • Fluid conductivity – salinity
  • Salt-water intrusion studies
  • Identification of fluid flow in open/cased hole
  • Localization of the water table
  • Localization of water intervals of different quality
  • Water-well monitoring
  • Geothermal gradient logging
  • Often used in the implementation of temperature compensation equations for other logs

Operating Conditions

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

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

[_] Required
[X] Not Necessary


Features & Benefits

  • In comparison with tools from competitors, this fluid temperature and conductivity tool is capable of recording a wide range of conductivity from fresh to highly saturated water.
  • Easy to calibrate. Measurements are accurate and consistent.
  • Operates on any standard wireline (mono, 4 or 7 conductor, coax)
  • Slim, 40 mm diameter. One-person operation.

Specifications – Metric/English

QL40-FTC Bottom sub

Specification Metric Imperial
Diameter 40 mm 1.6 in.
Length 0.81 m 32.1 in.
Weight 3.35 kg 7.2 lbs.
Max. Temp. 80ºC 176ºF
Max. Pressure 200 bar 2900 psi

QL40-FTC-I Inline sub

Specification Metric Imperial
Diameter 52 mm 2.05 in.
Length 0.94 m 37.1 in.
Weight 6.2 kg 13.7 lbs.
Max. Temp. 80ºC 176ºF
Max. Pressure 200 bar 2900 psi


Conductivity Sensor: Seven electrode mirrored Wenner array
Conductivity Range: 5 µS/cm to 300,000 µS/cm
Conductivity Accuracy: 1%

Temperature Sensor: Linear, fast-response semi-conductor
Temperature Range: -20 to 80ºC
Temperature Accuracy: < 1%
Temperature Resolution: 0.004ºC

QL Stack Possibilities

  • QL40FTC-I + QL4SFM (Spinner Flowmeter): Water-well Fluid flow studies
  • QL40FTC + QL40GR (Gamma): Water-well Monitoring, Contaminant Intrusion Studies
  • QL40FTC + QL40GR (Gamma) + QL40ELOG (Resistivity): Identification of Aquifers
  • QL40FTC + QL40GR (Gamma) + QL40ELOG (Resistivity) + QL40CAL (Caliper): Hydrogeologist’s Tool, Groundwater exploration, assessment, and well completion


Data Sheet
User Guide

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