1. n. [Formation Evaluation]

A rock whose petrophysical properties are well described by the Archie equation with constant values for the porosity exponent and the saturation exponent. Such rocks typically have very little clay, a regular pore structure, and high-salinity water. The term often is used to describe a rock that is petrophysically simple.

See: formation factor,  formation water,  resistivity index,  water saturation