1. n. [Formation Evaluation]

The porosity obtained by plotting two porosity logs against each other, normally density and neutron porosity. The computation assumes a particular fluid, usually fresh water, and particular response equations. The result is largely independent of lithology and is often a more reliable estimate of porosity than a single porosity log. It is often displayed as a quicklook log.

For more details, see The Defining Series: Measuring Porosity Downhole

See related terms: apparent matrix,  fresh water,  neutron porosity