1.
n. [Drilling Fluids]
Settling of particles in the
annulus of a well, which can occur when the
mud is static or being circulated. Because of the combination of secondary flow and gravitational forces, weighting materials can settle (
sag) in a flowing
mud in a high-angle well. If settling is prolonged, the upper part of a wellbore will lose
mud density, which lessens the hydrostatic
pressure in the hole, so an influx (a
kick) of
formation fluid can enter the well.