1. n. [Formation Evaluation]
The volume close to the borehole wall in which some or all of the moveable fluids have been displaced by mud filtrate. It consists of the flushed zone and the transition zone or annulus. In simple models, the invaded zone and the flushed zone are considered synonymous.
Antonyms: undisturbed zone, virgin zone
See: diameter of invasion, flushed zone, invasion, transition zone