1. n. [Drilling Fluids]

A type of nonreactive, easily differentiated material placed in a small portion of a circulating mud system at a certain time to be identified when it later returns to the surface from downhole. Mud tracers are used to determine mud cycle time (circulation time). Dyes, paints, beans, oats, chips, glitter or any material that will follow the mud and not be lost or destroyed can be used as a tracer. Care must be taken to use materials that do not dissolve, disperse or plug the bit or downhole motor. Mud tracers are distinct from mud-filtrate tracers.

See: cycle time,  filtrate tracer,  lag time,  tracer