TNPH
Schlumberger%Thermal Neutron Porosity
Thermal neutron porosity computed by the ratio method — the near-to-far detector count ratio, which cancels many borehole effects. A more environmentally robust neutron porosity than single-detector versions.
- 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
- ~0–0.6 CFCF
- porosity units, limestone-calibrated
Logging tool
No logging tool is associated with this curve.
Service company
Browse the full Schlumberger mnemonic dictionary, including legacy and current tool families.
View Schlumberger mnemonics →What is the TNPH curve?
How it's measured
A dual-spaced thermal neutron tool measures the ratio of near-to-far detector counts; the ratio, calibrated to limestone, converts to apparent porosity while suppressing borehole-size and standoff effects.
How it's used
Neutron-density crossplot porosity, lithology, and gas detection — the same role as NPHI but with ratio-method processing that improves accuracy in variable hole conditions.
Common gotchas
It still reads the hydrogen index, so gas reads low and shale reads high, and the limestone calibration needs a matrix shift. Environmental corrections remain necessary despite the ratio method.
In LAS files
Recorded as TNPH (or NPHI, CNL) in v/v or %. Note the calibration matrix (LS/SS/DOL).
Also seen with TNPH in real logs
Curves that appear alongside TNPH in the same wells across the public corpus.