When milling loose junk, spudding shall be periodically carried out to pound junk down to the bottom of the hole where it can be effectively milled. The following procedure shall be considerd:
Loose Junk
1. DETERMINE the neutral point where the mill is just above the junk. MARK the pipe.
2. PICK UP the pipe 3 - 6 ft.
3. DROP and CATCH the string just above the mark on the pipe.
Note: This action causes the string to stretch and spud the mill on the bottom.
4. SPUD 3 or 4 times turning the mill 1/4 turn each time.
An increase in torque is an indication that junk has worked alongside the mill. Spud the mill to free the tool.
Junk in Open Hole
The following guidelines shall be adhered to during milling junk in open hole:
When milling in open hole, the mill shall be only 1/8in to 1/4in less than the open hole diameter.
When possible, use at least 10 000 lbs of drill collars.
A junk sub or multiple junk subs shall be placed in the milling assembly.
Beware of casing shoes at deviations greater than 30o inclination. The junk sub may hang up whilst POOH.
Mill with 4 000 - 10 000 lbs depending upon the strength of the fish being milling.
After reaming the hole down, always set down on the fish while turning and bring the weight up to the milling weight without delay. Never apply weight without rotating first.
Do not stop milling by sitting on the fish with a light weight and spin. This causes the fish to work harden and restarting milling operations will be difficult. If milling has to stop for any reason, pick up the mill.
Junk Inside Casing
Similar conditions apply to milling junk in open hole with the addition of:
A non-rotating stabiliser or soft-bladed stabiliser shall be run above the mill with the same OD as the mill head.
The OD of the mill shall be approximately the same as the drift ID of the casing.
The wear parts on the mill should be the same OD as the OD of the mill head.
At least one junk sub shall be placed in the milling assembly.