MILLING OPERATIONS
Overview
Junk mills are the surest way to eliminate junk in the hole. There are various
mills that can be used in different circumstances. For example, the insert
type of mill is best suited for milling pipe or tools anchored securely in the
well bore; however, chatter, vibration or loose junk are detrimental to the
inserts.
mills that can be used in different circumstances. For example, the insert
type of mill is best suited for milling pipe or tools anchored securely in the
well bore; however, chatter, vibration or loose junk are detrimental to the
inserts.
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Types of Mills
1- Insert Type
Can be used for:
• pipe/tools anchored securely in the wellbore.
Caution: Chatter, vibration, or loose junk are detrimental to the
inserts.
• pipe/tools anchored securely in the wellbore.
Caution: Chatter, vibration, or loose junk are detrimental to the
inserts.
2- Crushed Tungsten Carbide Mills
Can be used for:
• almost anything, except in hard abrasive formations.
• almost anything, except in hard abrasive formations.
3- Skirted Flat Bottom Or Concave Type Mill
Can be used for:
• flared or burred top of fish prior to engagement with an
overshot. Because the skirted mill is stabilized and the
fish is contained within the skirt, it cannot slip off
• flared or burred top of fish prior to engagement with an
overshot. Because the skirted mill is stabilized and the
fish is contained within the skirt, it cannot slip off
4- Blade Type Mill
Can be used for:
• junk or cast iron material which will break up.
Features:
• Rugged, durable construction
• Concave, convex, and flat-bottom designs available
• Dressed with tungsten carbide inserts for stationary fish
or junk
• Dressed with crushed tungsten carbide for loose fish or
junk
• Improved cooling during milling
• Increased milling efficiency
• junk or cast iron material which will break up.
Features:
• Rugged, durable construction
• Concave, convex, and flat-bottom designs available
• Dressed with tungsten carbide inserts for stationary fish
or junk
• Dressed with crushed tungsten carbide for loose fish or
junk
• Improved cooling during milling
• Increased milling efficiency
5- Pilot Mill/Diamond Point
The Pilot Mill/Diamond Point is used for milling tubing, casing,
liner hangers, liners, drill pipe, drill collars, wash pipe, or
perforated liners.
Using Pilot Mills:
• Select a pilot mill with a blade O.D. ¼ inch larger than
the O.D. of the tool joint or coupling of the fish milled.
The pilot O.D. should be the same as the drift I.D. of the
fish.
• Determine the best rotary speed and weight to run a pilot
mill for each job. Conditions may change from one pilot
milling job to the next in the same well. The change may
require different rotary speeds and weights at different times. In the absence of experience, start with a speed of
between 80 and 100 RPM’s and a tool weight of 2,000
to 6,000 lbs. Vary the speed and weight to obtain the
best results.
• If milling a liner or casing that is gun-perforated,
damaged with a spear, or collapsed, use 60 RPM’s and
2,000 lbs. of weight or less.
• A sudden drop in the milling rate while milling swaged
casing may be caused by a loose ring of steel formed at
a joint or weld, which turns with the pilot mill. Spud the
mill gently to break up the ring and position it for
milling.
• If the milling rate stops or drastically slows down in the
milling of wash pipe, casing or liner without a
noticeable increase in torque, the fish may be turning.
• If so, pull the mill, and retrieve the fish with a spear.
liner hangers, liners, drill pipe, drill collars, wash pipe, or
perforated liners.
Using Pilot Mills:
• Select a pilot mill with a blade O.D. ¼ inch larger than
the O.D. of the tool joint or coupling of the fish milled.
The pilot O.D. should be the same as the drift I.D. of the
fish.
• Determine the best rotary speed and weight to run a pilot
mill for each job. Conditions may change from one pilot
milling job to the next in the same well. The change may
require different rotary speeds and weights at different times. In the absence of experience, start with a speed of
between 80 and 100 RPM’s and a tool weight of 2,000
to 6,000 lbs. Vary the speed and weight to obtain the
best results.
• If milling a liner or casing that is gun-perforated,
damaged with a spear, or collapsed, use 60 RPM’s and
2,000 lbs. of weight or less.
• A sudden drop in the milling rate while milling swaged
casing may be caused by a loose ring of steel formed at
a joint or weld, which turns with the pilot mill. Spud the
mill gently to break up the ring and position it for
milling.
• If the milling rate stops or drastically slows down in the
milling of wash pipe, casing or liner without a
noticeable increase in torque, the fish may be turning.
• If so, pull the mill, and retrieve the fish with a spear.
6- Tapered Mills
The Weatherford Standard Tapered Mill is designed for milling
through restrictions. The spiral blades and pointed nose dressed
with crushed tungsten carbide make the mill ideal for reaming
collapsed casing and liners, cleaning permanent whipstock
windows, milling through jagged or split guide shies, and
enlarging restrictions through retainers and adapters. The torque
encountered governs the tapered mill rotary speeds.
• To overcome torque challenges, do not exceed 75
RPM’s.
• Do not rotate a tapered mill resting on a fish. Enter the
fish with a rotary speed of 75 RPM’s ort less.
• Use less weight when running a tapered mill than a junk
or pilot mill. After entering the fish, increase the tool
weight to slowly to 1,000 to 2,000 lbs. Watch for any
torque increase.
through restrictions. The spiral blades and pointed nose dressed
with crushed tungsten carbide make the mill ideal for reaming
collapsed casing and liners, cleaning permanent whipstock
windows, milling through jagged or split guide shies, and
enlarging restrictions through retainers and adapters. The torque
encountered governs the tapered mill rotary speeds.
• To overcome torque challenges, do not exceed 75
RPM’s.
• Do not rotate a tapered mill resting on a fish. Enter the
fish with a rotary speed of 75 RPM’s ort less.
• Use less weight when running a tapered mill than a junk
or pilot mill. After entering the fish, increase the tool
weight to slowly to 1,000 to 2,000 lbs. Watch for any
torque increase.
7- Watermelon/String Mills
The Weatherford string mill is dressed with tungsten carbide
spiral blades tapered from top to bottom to enable reaming both
up and down in collapsed casing and liners. The lower
connection enables a stinger to be run below the tool to prevent
sidetracking. The mill can also be placed anywhere in a drill or
fishing string. The mill features crushed tungsten carbidedressed
reamer blades.
Can be used for:
• Smooth or rough OD
• Milling out collapsed areas in casing and liners
• Eliminating key seats and doglegs in open hole
• Extending whip stock windows
spiral blades tapered from top to bottom to enable reaming both
up and down in collapsed casing and liners. The lower
connection enables a stinger to be run below the tool to prevent
sidetracking. The mill can also be placed anywhere in a drill or
fishing string. The mill features crushed tungsten carbidedressed
reamer blades.
Can be used for:
• Smooth or rough OD
• Milling out collapsed areas in casing and liners
• Eliminating key seats and doglegs in open hole
• Extending whip stock windows
8- Flat Bottom Cone Buster
Mill
Mill
This flat bottom cone buster mill is dressed with crushed
tungsten carbide and is a very aggressive mill used to mill up bit
cones or other pieces of junk. The mill is sturdy enough for
light spudding on the junk to break it up into smaller pieces.
Large circulation ports improve mud circulation for cooling and
for the removal of cuttings. Field reports show these long
lasting mills are safer than using a rock bit because you can’t
lose any bit cones in the hole. Weatherford’s junk mills work
well when milling drillable packers, bridge plugs, retainers, and
cement.
Note: Important characteristics of cone buster mills include that
they can be furnished with:
tungsten carbide and is a very aggressive mill used to mill up bit
cones or other pieces of junk. The mill is sturdy enough for
light spudding on the junk to break it up into smaller pieces.
Large circulation ports improve mud circulation for cooling and
for the removal of cuttings. Field reports show these long
lasting mills are safer than using a rock bit because you can’t
lose any bit cones in the hole. Weatherford’s junk mills work
well when milling drillable packers, bridge plugs, retainers, and
cement.
Note: Important characteristics of cone buster mills include that
they can be furnished with:
- large circulation ports which improve mud circulation for
- smooth outside diameter along with stabilizer pads designed
9- Cement Mills
Can be used for:
• Milling cement
• Milling cement
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