This is a well log used in the oil and gas industry. The acronym NPL can be found in any (ASCII) log files provided by the logging company. Enhanced Thermal Neutron Porosity in Selected Lithology is the offical name for this log. This log is not often acquired after (or during) drilling a well.

The values of this log represent the porosity as measured with a thermal neutron logging device.

Concluding, this is a measure of the porosity as measured with an neutron logging device. At a more general level these values are measures of the apparent porosity. This can be explained as being the initial estimate of porosity, normally from logs, not corrected for the (often large) effects of clays, gas, etc. Such estimates should only be used for qualitative interpretation of clean, gas-free intervals. In general this log therefore displays units of the volume fraction. In other words, the ratio of the volumes occupied by two components, or by one component to the total volume of the system.

This log usually has the unit 'Porosity'. This is the pore volume per unit gross volume. Porosity is determined from measurements on cores or interpreted from logs.

Data for this log is produced by a tool that uses a neutron logging technique and can be used to investigate the porosity of the formation. Similar logs are listed below:

• APS High Resolution Near/Far Corrected Dolomite Porosity (HFMC)
• Real-Time CNP (Sandstone Matrix) (RNS)
• APS Near/Array Corrected Dolomite Porosity (APDC)
• APS Near/Far Uncorrected Sandstone Porosity (FPSU)
• Smoothed Near Detector ONLY Porosity (Limestone Matrix-Fixed Hole Size) (SNLF)
• Thermal Neutron Porosity (Ratio Method) in Selected Lithology (TNPH)
• Neutron Borehole Invariant Porosity (BNPH)
• APS High Resolution Near/Array Corrected Limestone Porosity (HALC)
• Smoothed CNP (Limestone Matrix-Caliper Corrected) (SPLC)
• Smoothed CNP (Dolomite Matrix-Fixed Hole Size) (SPDF)