This is a well log used in the oil and gas industry. The code
PO1B is a unique identifier to recognize this particular log and can be found in any (ASCII) log files provided by the logging company. The acronym stands for
'Partial porosity from MRIL (single element)'. This log is very common in the industry. Use this log to investigate the contribution of porosity from a given "bin" (with certain characteristics) to the total porosity; e.g., in nuclear magnetic resonance data processing, the "bins" typically correspond to different pore size ranges. In general this log therefore displays units 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.
So basically this is a measure of the pore volume per unit gross volume. Porosity is determined from measurements on cores or interpreted from logs.
Furthermore, this can be explained by looking at the volume fraction. This is a measure of the ratio of the volumes occupied by two components, or by one component to the total volume of the system.
Data for this log is produced by a tool that uses a nmr logging technique and can be used to investigate the porosity of the formation. Similar logs are listed below: