ROLLING CUTTER BITS Rolling Cutter Bits –Steel Tooth (milled tooth) –Carbide Tooth (tungsten...
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Transcript of ROLLING CUTTER BITS Rolling Cutter Bits –Steel Tooth (milled tooth) –Carbide Tooth (tungsten...
ROLLING CUTTER BITS
• Rolling Cutter Bits
– Steel Tooth (milled tooth)
– Carbide Tooth (tungsten carbide insert)
• Introduced in 1909 by Howard Hughes
– 2 - cone bit
– Not self-cleaning
Tungsten Carbide Insert Bit
Milled ToothBit
ROLLING CUTTER BITS
• The three-cone rolling cutter bit is by far the most
common bit
• Large variety of tooth design and bearing types
• Maximum use is made of limited space
• Cone offset to stop rotating periodically to scrape
the hole like (PCD) bits
• It increases drilling speed but tooth wears faster. (4
for soft, 0 for hard)
ROLLING CUTTER BITS
• Shape of teeth: long widely spaced steel teeth are
used for drilling soft formations
• As the rock type gets harder the tooth length and
cone offset must be reduced to prevent tooth
breakage
• Tooth action = Scraping and twisting
• Zero offset cones action = Crushing
• Smaller tooth allows more room for the
construction of stronger bearings
Classification of Tricone Bits(a)(a) Milled tooth cuttersMilled tooth cutters
(b)(b) Tungsten carbide insert cuttersTungsten carbide insert cutters
• Hard facing on one side of the tooth allows self
sharpening
• Chipping tends to keep tooth sharp
• Intermeshing is advantageous.
• Heel teeth = outer-raw very difficult job it wears it
leads to out of gauge bit (hole)
Example tungsten carbide insert cutter Example tungsten carbide insert cutter used in rolling cutter Bitsused in rolling cutter Bits
ROLLING CUTTER BITS• Improvements
– 3 - cone bit (straighter hole)
– Intermeshing teeth (better cleaning)
– Hard-facing on teeth and body
– Steel Tooth (milled tooth)
– Carbide Tooth (tungsten carbide insert)
– Change from water courses to jets
– Tungsten carbide inserts
– Sealed bearings
– Journal bearings
ROLLING CUTTER BITS
• Advantages
– For any type of formation there is a
suitable design of rock bit
– Can handle changes in formation
– Acceptable life and drilling rate
– Reasonable cost
Fluid flow through water courses in bit
Proper bottomhole cleaning is
very important
Fluid flow through jets in the bit (nozzles)
ROLLING CUTTER BITS• Milled Tooth Bit (Steel Tooth)
– Long teeth for soft formations
– Shorter teeth for harder formations
– Cone off-set in soft-formation bit results in
scraping gouging action
– Self-sharpening teeth by using hard-facing
on one side
– High drilling rates - specially in softer rocks
Milled Tooth Bit
(Steel Tooth)
ROLLING CUTTER BITS
• Tungsten Carbide Insert Bits
– Long life cutting structure in hard rocks
– Hemispherical inserts for very hard rocks
– Larger and more pointed inserts for softer rock
– Can handle high bit weights and high RPM
– Inserts fail through breakage rather than wear
– Tungsten carbide: very hard, brittle material
Tungsten
Carbide Insert Bits
Roller Cone Bearings
Bearings
• Ball Bearings (point contact)
• Roller Bearings (line contact)
• Journal bearing (area contact)
• Lubrication by drilling fluid . . . or . . .
Bearings
Sealed Bearings (since 1959) Grease lubricant (much longer life)
Pressure surges can cause seal to leak!
Compensate?
Journal Bearings (area contact) Wear-resistant hard surface on journal
Solid lubricant inside cone journal race
O - ring seal
Grease
Grading of Dull Bits How do bits wear out?
• Tooth wear or loss
• Worn bearings
• Gauge wear
Grading of Dull BitsHow do bits wear out?
• Steel teeth - graded in eights of original tooth height that has worn away
e.g. T3 means that 3/8 of the original tooth height is worn away
Grading of Dull Bits Broken or Lost Teeth
• Tungsten Carbide Insert bit
e.g. T3 means that 3/8 of the inserts are broken or lost
Grading of Dull Bits How do bits fail?
• Bearings: B3 means that an estimated 3/8 of the bearing life is gone
Balled up Bit Cracked Cone
Grading of Dull Bits How do bits fail?
Washed out Bit Lost Cone
Grading of Dull Bits How do bits wear out?
Examples:
• T3 – B3 - I
• T5 – B4 - 0 1/2
• Gauge Wear:• Bit is either in-Gauge or out-of-Gauge• Measure wear on diameter (in inches),
using a gauge ring
BIT
GAUGE RING