This is an abbreviation for a well log acquired after or during drilling. You could find this abbreviation
PO2C in your log evaluation software or any (ASCII) log files provided by the logging company.
Partial porosity from MRIL (single element) is the full name for this log. This log is very common in the industry. This log displays readings of 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. At a higher level, this can be seen as a measure of the apparent porosity. This is a measure of 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. In general this is a measurement of the volume fraction. This can be explained as being 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: