1. n. [Formation Evaluation]

A transform from raw log data chosen so that a log recorded in these units will give the correct porosity of the formation, providing the matrix is pure calcite and the pores are filled with fresh water. The unit, which may be in vol/vol or p.u., is most commonly used for neutron porosity logs but may also be used for density and acoustic logs. The definition is strictly true only if all borehole and other environmental corrections have been applied.

See related terms: acoustic log,  fresh water,  limestone-compatible scale,  neutron porosity,  sandstone porosity unit,  sandstone-compatible scale