More than half of all coiled-tubing jobs are wellbore cleanouts. A significant number of these operations are performed using workover motors and milling assemblies. While the value of a milling assembly is well documented, down-hole conditions such as high temperatures (above 400 °F) and hostile fluids can significantly reduce the life of a workover motor and limit milling operations. Impact-drill systems are an attractive alternative because they perform reliably in adverse conditions. The most common applications of the impact drill include scale milling, hard-cement milling, resin-sand removal, and gravel removal.