1. adj. [Formation Evaluation]

A system that has reached equilibrium for the measurement or phenomenon concerned. In the case of permeability measurements on core samples, a steady state is reached when the flow rate, the upstream and the downstream pressures no longer change with time. At this point the permeability can be calculated from the flow rate and pressures and applying Darcy's equation. If gas is used, the inertial resistance and gas slippage (Klinkenberg effect) should be corrected for.

Antonyms: unsteady state

See related terms: core plug,  permeameter,  routine core analysis