(1) (n.) Drilling Fluids. A fluid that is left in the annular region of a well between tubing and outer casing above a packer. The main functions of a packer fluid are: (1) to provide hydrostatic pressure in order to lower differential pressure across the sealing element, (2) to lower differential pressure on the wellbore and casing to prevent collapse and (3) to protect metals and elastomers fromcorrosion. See: Differential Pressure, Hydrostatic Pressure. (2) (n.) Well Completions. The fluid that remains in the tubing-casing annulus above the packer after the completion has been run and all circulation devices have been isolated. Packer fluids are prepared for the requirements of the given completion. Generally, they should be of sufficient density to control the producing formation, be solids-free and resistant to viscosity changes over long periods of time, and be noncorrosive to the wellbore and completion components