1. n. [Formation Evaluation]

A calculation of the properties of the solid fraction of a rock from the combination of two logs. For example, by combining the density and neutron porosity measurements, it is possible to compute an apparent matrix density; by combining neutron porosity and sonic measurement, it is possible to compute an apparent matrix traveltime. The computations assume a particular fluid, usually fresh water, and particular response equations. The results are often displayed as quicklook logs for lithology identification. The word matrix is used here in the formation evaluation sense of the term rather than the geological one.

See: crossplot porosity