PEF
Schlumberger%Photoelectric Factor
The photoelectric absorption cross-section — a near-direct lithology indicator: about 1.8 for sandstone, 5 for limestone, 3 for dolomite, and very high for barite mud or heavy minerals. It is nearly independent of porosity.
- Property
- Photoelectric Factor
- Property
- Quantity
- dimensionless
- % · GEuc · ppm · mEuc · cEuc · MEuc · nEuc · pEuc · kEuc · ppk · fEuc · µEuc · dEuc · EEuc · TEuc · Euc
- Typical range
- ~2–5.1 BARNS/E
- barns/electron, by lithology
Logging tool
No logging tool is associated with this curve.
Service company
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View Schlumberger mnemonics →What is the PEF curve?
How it's measured
Recorded on the density tool from low-energy gamma absorption (the photoelectric effect), which depends on average atomic number — hence lithology — rather than density.
How it's used
Matrix and lithology identification, especially separating limestone from dolomite, and refining density-neutron interpretation. Combined with density and neutron in mineral-solving models.
Common gotchas
Barite-weighted mud swamps the PEF with very high absorption, making it useless in washed-out or barite-mud holes. It is a shallow pad measurement, so borehole rugosity degrades it.
In LAS files
Recorded as PEF (or PE, PEFZ) in barns/electron. If PEF reads absurdly high, suspect barite mud rather than heavy minerals.
Also seen with PEF in real logs
Curves that appear alongside PEF in the same wells across the public corpus.