1. n. [Well Workover and Intervention, Drilling]

The use of a mill or similar downhole tool to cut and remove material from equipment or tools located in the wellbore. Successful milling operations require appropriate selection of milling tools, fluids and techniques. The mills, or similar cutting tools, must be compatible with the fish materials and wellbore conditions. The circulated fluids should be capable of removing the milled material from the wellbore. Finally, the techniques employed should be appropriate to the anticipated conditions and the likely time required to reach the operation objectives.

See: casing string,  junk,  mill out,  packer