ILD
SchlumbergerΩ·cmDeep Induction Resistivity
Deep-reading induction resistivity — the classic true-resistivity (Rt) estimate for water-saturation calculation in fresh-mud and oil-based environments. It reads high in hydrocarbon-bearing or tight rock and low in saline water-bearing zones.
- Property
- Deep Induction Resistivity
- Deep Resistivity
- Quantity
- electrical resistivity
- Ω·cm · kΩ·m · Ω·m²/m · nΩ·mm²/m · Ω·m · nΩ·mil²/ft
- Typical range
- ~1.3–500.9 ohm·m
- ohm·m, from water-bearing (low) to hydrocarbon or tight (high)
Logging tool
No logging tool is associated with this curve.
Service company
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View Schlumberger mnemonics →What is the ILD curve?
How it's measured
Transmitter coils induce eddy currents in the formation; receiver coils sense the resulting signal, giving conductivity (inverted to resistivity). The deep array reads past the invaded zone toward true resistivity Rt.
How it's used
Primary Rt input to Archie water saturation, hydrocarbon identification, and — with the medium and shallow curves — invasion profiling. It performs best in fresh muds and moderate resistivities.
Common gotchas
Induction loses accuracy at very high resistivity and in salty (conductive) muds, where laterolog tools are preferred. It needs skin-effect and borehole corrections, and thin beds are averaged.
In LAS files
Recorded as ILD (or RILD, RT, AT90) in ohm·m. Medium (ILM) and shallow curves usually accompany it for invasion analysis.
Also seen with ILD in real logs
Curves that appear alongside ILD in the same wells across the public corpus.