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Normal Resistivity + SP Tool (Elog)
This tool measures the resistivity of the material surrounding the borehole. Three logs are produced, Point Resistance (PR), 0.5m Normal (0.4m NR) and 1.6m Normal (1.6m NR), each having a different radius of investigation and resolution.
The point resistance has the greatest resolution and least radius of investigation and the 1.6m Normal has the least resolution but greatest radius of investigation.
The response of this log is a function of porosity, mineralogy and pore water quality. In metal lined boreholes the resistivity can give qualitative information on the condition of the casing and may be used to identify areas of increased corrosion on encrustation.
A Spontaneous Potential (SP) measurement can also be recorded. This measures the differences in the electrical potentials caused by electrochemical differences between the borehole fluid and the formation pore-fluid, mineralogy of the formation, lining material or electrokinetic effects of fluid flow. In metal lined holes the log may be used to locate intervals of active corrosion.
Specifications
Logging Conditions
- 4 – 9 m/min
- Free running
- Minimum fluid filled interval 20m due to ref. electrode / bridal distance
Borehole Conditions
- Fluid filled
- Unlined
Lithological identification
The effects of differences between borehole fluid and pore fluid quality