Pilot Mills - Description and Usage
Parveen Pilot Mills dressed with Tungsten carbide are recommended for milling washpipe, safety joints, crossover swage and washover shoes. Liner hangers can be milled efficiently, eliminating inside cuts and running spears or jars. The nose, or pilot, can be dressed to mill out junk which may be encountered.
Use Pilot Mills to mill :
General Guidelines for Using Pilot Mills
! In selecting a Pilot Mill, the blade O.D. should be about 1/4" larger than the O.D. of the tool joint or coupling of the fish to the milled. The pilot O.D. should be the same as the drift diameter of the fish.
! The best speed and weight to run a pilot Mill must be determined for each job. Also, conditions may change from one pilot-milling job to the next in the same well. This may require different speeds and weights at different times. In the absence of experience, start with a rotary speed between 80 and 100 RPM and tool weight of 2,000 to 6,000 lbs. Experiment to obtain the best results.
! When milling a liner or casing that has been gun perforated, damaged with a spear, or collapsed, use 60 RPM and
2,000 lbs. of weight or less.
! If, when milling swaged casing, you experience a sudden drop-of in milling rate, the trouble may be caused by a loose ring of steel formed at a joint or weld which is turning with the Pilot Mill. Try spudding the Pilot Mill gently. This should break up the ring and help position it for milling.
! If cutting stops altogether when milling washpipe, casing or liner, and there is no noticeable increase in torque, there is a good chance the fish is turning. If this is the case, pull the mill and attempt to retrieve the fish using a spear.
Considerations When Milling Liner, Hangers and Adapters
On most liner milling jobs, a Pilot Mill is used to first mill the liner hanger or adapter and then the liner. In some cases the liner hanger or adapter is milled using Junk Mill. Then the liner is milled with a Pilot Mill. This latter method is preferred if there is hard cement behind the liner or if the hanger has numerous bowsprings, slips, etc. Select a Pilot Mill with blades that will cut just over the pipe couplings. This will result in a minimum of cement being encountered.
A Pilot Mill is Ideal for Wash Pipe
The Pilot Mill is the most efficient tool for milling stuck washpipe. If drill pipe or drill collars are inside washpipe, however, they must first be milled with a Junk Mill or smaller Pilot Mill.
Milling Drill Pipe and Drill Collars
Drill pipe and drill collars are sometimes milled with Pilot Mills, if the I.D. is open. If the drill pipe is cemented inside the casing, particularly in deviated holes, the pipe is probably lying to one side with its center eccentric to the casing. Most often this makes the job extremely difficult for a Pilot Mill. Under these conditions, we recommend a full gauge Junk Mill. A Pilot Mill will do a reasonable job on drill collars, provided the cuttings can be removed as the milling progresses. If cuttings tend to fall into the I.D. and plug it, then a Junk Mill must be used.
Casing can be milled with a Pilot Mill in the same manner that washpipe is milled.