Tri Cone

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THE BIT
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ADC DAD Program

6/24/2010
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Introduction To Bit
• Function of a Bit:
• Drill a gauged hole and circulate mud through it to carry cuttings to surface.
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• ROP, Longevity and Gauge: Higher Rate of penetration and long life of
bit are primary concerns of an operator. If bit wears out from sides, an
under gauge hole is drilled which causes restriction or pipe sticking.
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Formations and Bit Design: Bit selection depends on formation types
i.e hard, soft, abrasive, sticky. Different bits are run for different type of
formations.
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Introduction To Bit (cont’d)
Choosing a Bit:
• Guess work when drilling wild cat well.
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• offset well data
• Cost factor
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Bit Classification
Drill Bits
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Fixed Rolling
Cutter Cutter
P.D.C. l.c Diamond Milltooth Insert

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Roller Friction
Natural Impregnated Bearing Bearing
T.S.P.
Diamond Diamond
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Bit Classification
Drill Bits
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Fixed Rolling
Cutter Cutter
l.c P.D.C. Diamond Milltooth Insert

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Roller Friction
Natural Impregnated Bearing Bearing
T.S.P.
Diamond Diamond
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Roller Cone Bits
• Roller cone bits and rock bits are the same.
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•Roller cone bits may have two or three cones
• Each cone rotates on its own axis making the
cutters scrape, gouge, or crush the formation to
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•Intermesh of cutters help clean each other.
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History
& Drag bit or fish tail was in use till 1906.

& The 1st roller cone bit came into use in 1906.
& Bits with two cones get balled up in soft formation.
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& Water course was getting worn-out with abrasive material So a wash pipe
was installed which has a very hard coating inside.
&The three cone bit came in use in 1930s.
& Three cone bit was having bearings which were getting lubricated with drilling
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fluid and with different type of cutters.
& Penetration increases when bottom of hole and bit’s cutters are clean and so,
nozzles were introduced for the same purpose.
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& Different size of nozzles i.e 9/32” etc.
& In large size bits, extended nozzles overcome loss of hyd. Power and helps
prevent balling in of bits.
& Center nozzle also helps prevent balling up by better cleaning of cutters.
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Roller Cone Components

Nose Cone #1
Cone #3
Gage Row Inner Row
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Heel Row
Cone #2
Shirttail
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Bit Bowl
Pin Bit Body

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Hydraulic horse Power
Bit Hydraulic Horse Power is limited by:

1. High pump maintenance cost
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2. Erosion/wash out of DP, swivel packing and other components
3. Pump size and power
4. Lowest speed of mud required to return cuttings to surface by avoiding
turbulent flow.
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5. Small dia. nozzles get plugged more easily as compared to big dia.
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OFFSET CONES
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Bit gauge
•Outer row is called gauge row or heal row.

•Unlike other rows, the gauge row cutter do not
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intermesh and may normally have missing teeth to create
more space between the cutters.
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Cutters
•Long teeth are desirable in soft formations.

•Long teeth do not break in soft formations.
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•Long teeth gives scraping and gouging action which
increases ROP.
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•Short teeth punches into the hard formation. Can not
scrap and gouge. Do not break against hard formation.
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Cutting Elements
Teeth and hardfacing
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Scrapping and Gouging
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Drilling Mechanisms vs Bit Type
Scraping Mill Tooth
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Chipping and Crushing Insert
Shearing PDC
Ploughing
l.c Natural Diamond
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Grinding Impregnated Diamond
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Bearings:
Friction between two surfaces rubbing against each other, results into slow down of
movement, heats up surfaces and wears them away.
Three Types of Bearings
1. Ball Bearings 2. Roller Bearings 3. Journal Bearings
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1. Ball Bearings:
1. Ball Bearings: Hard steel balls, being machined deeper into cone body, lock the
cone on the bits leg.
2. Roller Bearings: Solid Cylinders of metal, rotates freely in the race
3. Friction Bearings:
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Also called Journal bearings. Journal bearing as a main bearing. Some bits also use
ball bearings to hold the cone onto the bit and some eliminates ball bearings by
using a metal ring. Journal bearings consist of flat and polished surface to minimize
the friction. Special alloy such as copper and silver is inserted which under the high
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heat and pressure melt to provide heavy duty lubricant for the journal bearing.
• Journal bearings, having more contact area than roller bearings are much stronger
than roller bearings. Example rolling a glass on a table Vs putting your hand flat on
a table
• Bits with Journal bearings have now an unlimited life provided lubrication system
does not fail.
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Roller Bearings
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Friction or Journal Bearings
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Roller cone bit – Journal Bearing
Main Bearing
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Retention Bearing
Thrust Bearing
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Pin Bearing
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Bearing Lubrication:
Non Sealed Bearings: No seal exists between bit shirt tail and cone. Mud
enters into bearing race and lubricates bearing. Unfortunately abrasive material
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in the mud cause abrasion to bearing parts and hence shorten the bit life.
Sealed Bearings: Seals off with metal or synthetic rubber. Reservoir of grease
feeds grease to bearing. Reservoir and lubrication system has two functions. 1.
lubrication and 2. Equalizes pressure inside sealed bearing with the pressure
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in the hole with the help of pressure compensator.
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Bearing Lubrication (cont’d)
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Wear on a Bit
It is important to know about the kind of damage to bit to adopt the correct course of
action for future planning. Parts of a bit that can fail are cone, cutters and bearings.
1. Cone wear:
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• Cone skidding or Dragging: when a cone locks, flattens the part of cone > balling
up of bit, junk lodged between cones.
• Cone Interference: Cones bent inwards and lock with each other i.e reaming under
gauge hole with excessive WOB, causes broken cutters or cracked cones.
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inserts to fall out. l.c
Cone Erosion: Occurs due to high velocity of fluid and abrasive cuttings causing
Cracked Cones: due to severe erosion, dented with junk in hole, bit hitting a ledge,
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hitting btm of hole hard, over heating due to cone interference and chemical erosion
due to H2S.
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Wear on a Bit (cont’d)
Off Center Wear: Extra wear between two rows of cutters or wear on gauge
area of a cone. When ROP is too low in soft or medium soft formation either due
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to less WOB or less RPM causing the bit to whirl. Whirling is a motion when a bit
does not rotate around its own axis. Whirling drills an over gauged hole, two
cones drills btm of hole and one side of wall.
Cone Coring: Inside row or nose of a cone wears or breaks due to junk in the
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hole, cone erosion, improper breaking in of a bit.
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Cutter Wear
Inserts or tooth of a bit are broken due to wrong bit selection, junk in hole, hard
formation, excessive WOB, Improper break in of a bit.
Broken Inserts: Due to high rotary speed in hard formation, usually gauge row inserts are
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broken (should reduce speed).
Broken Teeth: indicates wrong selection of the bit for the formation or wrong drilling
practices.
Chipped Cutters: due to rough drilling conditions. Fairly common and indicates generally
no problem.
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Flat Crested Wear: When top of the teeth are evenly wear out.
Self Sharpening Wear: The drilling mud abrades the softer metal on one side of each tooth
which is desirable.
Heat Checking: Small cracks on cutters which result from cutters repeated dragging and
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getting cooled down by mud.
Gauge wear: While drilling abrasive formation at high RPM and while reaming an under
gauge hole. In extreme cases, bearings are lost.
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Bearing Wear
Both outer and inner bearings can fail if WOB is too high, RPM too fast, reaming under
gauge hole, abrasive drilling fluid and bit using for long period.
Outer Bearings (the roller or Journal bearings under the gauge cutters) can fail due to:
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• Excessive rotation time coupled with heavy weight.
• Abrasive drilling fluid can damage non sealed bearings.
• Skid marks or lock cones are the signs of outer bearings failure
Inner Bearings: The inside roller bearings and nose bearing can fail:
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• While drilling a formation which is too hard for it. Tooth gets flat crested wear and
drillers add more weight to get more ROP resulting in damaging the inner bearings.
• Gauge rounding off of gauge cutters shift strong forces of rotation and weight on weaker
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part of bearing which is inner bearing
• Reaming of under gauge hole.
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Bits Grading
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Dull Bits Grading
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Field Operating Procedures

Life of a bit cuts short, if not handled properly. Following precautions to be taken.
• Check the type of bit and threads of bit on the bit box or bit shank.
• Use lifting cap to lift the bit to rig floor.
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• Clean the lubricant on the threads and use proper dope.
• Install correct nozzles and ensure snap rings are in place.
• Use correct bit breaker for the type of bit.
• Screw the bit (small size) by hand directly into the bit sub made up to stand of
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drill collars. Try to avoid rty table to screw the bit as either threads can get
damaged or bit may fall into well bore.
• For bit size 12” and above, cover the hole and lock RTY table. Keep the bit on
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rotary cover and screw the bit sub onto the bit threads with chain tong.
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Field Operating Procedures (cont’d)
• Remove hole cover and install bit breaker in RTY table. Lower the
bit into breaker. Set the make up tong on bit sub and turn RTY table
anti clock wise until bit is fully made up.
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• lock the RTY table and apply correct bit make up torque.
• Lower the bit carefully through BOP stack, TOL and in open Hole
avoiding any damage to bit.
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• Ream down with less weight and low RPM if hole is under gauge.
• Wash down with full circulation rate to clean the btm of hole prior
to commence drilling. Rushing this step can cause the bit to ball up
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and plugging the nozzle.
• Break in the bit prior to apply full drilling parameters.
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https://oil-com.blogspot.

ADC DAD Program

ADC DAD Program

Introduction To Bit (cont’d)

ADC DAD Program

P.D.C. l.c Diamond Milltooth Insert

ADC DAD Program

l.c P.D.C. Diamond Milltooth Insert

ADC DAD Program

Roller Cone Bits

• Roller cone bits and rock bits are the same.

ADC DAD Program

& Drag bit or fish tail was in use till 1906.

ADC DAD Program

Roller Cone Components

Pin Bit Body

Hydraulic horse Power

Bit Hydraulic Horse Power is limited by:

ADC DAD Program

ADC DAD Program

•Outer row is called gauge row or heal row.

ADC DAD Program

•Long teeth are desirable in soft formations.

ADC DAD Program

Teeth and hardfacing

ADC DAD Program

Scrapping and Gouging

ADC DAD Program

Drilling Mechanisms vs Bit Type

Scraping Mill Tooth

ADC DAD Program

ADC DAD Program

Friction or Journal Bearings

ADC DAD Program

Roller cone bit – Journal Bearing

ADC DAD Program

ADC DAD Program

Bearing Lubrication (cont’d)

ADC DAD Program

ADC DAD Program

Wear on a Bit (cont’d)

ADC DAD Program

ADC DAD Program

ADC DAD Program

ADC DAD Program

Dull Bits Grading

ADC DAD Program

Field Operating Procedures

ADC DAD Program

Field Operating Procedures (cont’d)

ADC DAD Program

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