NPHI
Schlumberger%Tool: DSNT-UHPNeutron Porosity
Apparent porosity from the formation's hydrogen index. Calibrated to limestone, it reads true porosity in clean wet limestone and departs elsewhere and in gas — the basis of the neutron-density crossplot that anchors lithology and gas detection.
- Property
- Thermal Neutron Porosity
- Neutron Porosity
- Quantity
- dimensionless
- % · GEuc · ppm · mEuc · cEuc · MEuc · nEuc · pEuc · kEuc · ppk · fEuc · µEuc · dEuc · EEuc · TEuc · Euc
- Typical range
- ~0.1–38.5 pu
- porosity units, limestone-calibrated
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How it's measured
A neutron source emits fast neutrons that are slowed mainly by hydrogen; near and far detectors count the thermal neutrons returning. More hydrogen (pore fluid) yields higher apparent porosity.
How it's used
Paired with density for lithology and gas (the neutron-density crossover), and for porosity in known lithology. It is one half of nearly every quick-look porosity and lithology workflow.
Common gotchas
It reads the hydrogen index, not porosity directly — gas (low hydrogen density) reads too low, shale reads too high from bound water, and the limestone calibration must be shifted for sandstone or dolomite. Environmental corrections matter.
In LAS files
Recorded as NPHI (or TNPH, CNL, PHIN) in v/v or %. Note the matrix (LS/SS/DOL) the log was calibrated to.
Also known as
Variants of NPHI seen in real LAS files — PetroCurve maps each of these on import.
Based on 53,375,297 samples in the public corpus.
Also seen with NPHI in real logs
Curves that appear alongside NPHI in the same wells across the public corpus.