This is an abbreviation for a well log acquired after or during drilling. You could find this abbreviation
PO7D in your log evaluation software or any (ASCII) log files provided by the logging company. The acronym stands for
'Partial porosity from MRIL (single element)'. The usage of this log is well established. This log helps to evaluate 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.
Concluding, 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: