Junk Milling

Junk Milling - Description and UsageThe Junk Mill, dressed with Tungsten Carbide chews its way through the toughest drilling materials. It is often said to be the true workhorse of down hole milling operations.When drill pipe is cemented inside and out, a Junk Mill is the only tool will do the work. However, if the drill collars or drill pipe are not collapsed and the I.D. is open, a Pilot Mill can sometimes be used to better advantage. Often you can get better results with a Pilot Mill on wash pipe as well.When casing has been milled with a Pilot Mill to the point where it begins to rotate, it can often be pounded down and milled using a Junk Mill made up on the end of a length of slightly eccentric or bent drill pipe.Packers, testers, and bridge plugs can usually be milled in a few hours using a Junk Mill.Use Junk Mills to mill almost anything in the hole, including:
Bailer Cement Packers SubsBit Cones Drill Collars Reamers (shot length) TestersBits Drill Pipe Setting Tools WashpipeCalipers Hangers Slips WhipstocksCasing (collapsed) Jars String shots
General Guidelines For Using a Junk MillWhen milling loose junk, operations can be improved by frequent spudding. This action willpound the junk onto the bottom, positioning it for more effective milling.Never permit a sliver of junk to lodge next to the mill. Force it down by spudding the mill. A noticeable increase in torque will indicate that junk is alongside the mill.Picking up the mill and lowering it periodically will decrease the possibility of a deep-wear pattern developing the face of the mill. Instead it forces a new wear pattern to develop, thus evening the wear on the mill face.When milling cast-iron bridge plugs, the mill O.D. should be approximately 1/8" under the size of the bridge plug - this will prevent " skinning" the casing.
Step by Step Junk Milling Procedures1. Feel for the bottom, spud the junk, "kick in the pumps"; the same as for normal drilling conditions.2. Begin rotation at 60-80 RPM.3. Begin weight at 4, 000 lbs.4. If there is an indication junk may be turning, spud two or three times.5. After milling one or two feet, pick up the Kelly fifteen to twenty feet off the bottom and reduce pump pressure or shut of pumps (depending on hole conditions). This action will let the loose junk settle to the bottom.6. Once again feel for the bottom and spud. Begin rotation at 80-100 RPM using normal pump pressure. Begin weight at 4, 000-6, 000 lbs.7. Repeat steps 3 and 4 every few feet Procedures from here on will be governed by feel.
NOTE: In hard formation it will take fewer feet of hole to mill up the junk than in softer formation. This difference is due to junk more readily penetrating the softer formation.Recommendations for Milling Junk Loose Junk in Open Hole
- Use a junk mill with an O.D. of 1/8" less than hole diameter.

- Use at least 10, 000 lbs. of drill collars.
* Run a junk sub directly above the mill. (Please note: junk subs for 4-3/4" and smaller drill collars are not strong enough for repeated spudding.)