Drilling and Well Completion
Drilling Bits
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Drilling bit : The cutting or boring tool which is made up on the end of
the drillstring
TYPES OF DRILLING BIT
Drag Bits
Roller Cone Bits
Diamond Bits
Drilling and Well Completion – Dr. Abhay Sharma
1
Drilling Bits
Roller Cone Bits
The cutting action is provided by cones which rotate on the bottom of
the hole and drill hole with a grinding and chipping action.
Milled tooth bit Insert bit
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Roller Cone Bits
The cutting action is provided by cones which rotate on the bottom of
the hole and drill hole with a grinding and chipping action.
Drilling and Well Completion – Dr. Abhay Sharma
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Drilling Bits
Diamond Bits
Natural Diamond Bits
PDC Bits : Polycrystalline diamond compact
TSP Bits : Thermally Stable Polycrystalline
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Elements of Roller Cone Bit
• Bearing assemblies
• Cones
• Cutting elements
• Fluid circulation
Drilling and Well Completion – Dr. Abhay Sharma
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Drilling Bits
Bearing assemblies
Three Bearings used in
these bits:
• Roller bearings in outer
assembly helps to support
the radial loading
• Ball bearings resists
longitudinal or thrust loads
and helps to secure the
cones on the journals
• Friction bearing, in the
nose assembly
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Bearing assemblies
Drilling and Well Completion – Dr. Abhay Sharma
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Drilling Bits
Bearing assemblies
Roller bearings, Ball bearings, Friction bearing
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Lubrication in Bearing assemblies
Open system : circulation fluid come in contact with bearings
Sealed system : Circulation fluid remains isolated
Drilling and Well Completion – Dr. Abhay Sharma
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Drilling Bits
Elements of Roller Cone Bit
•
Hollow inside for bearings
Cutters on cone body
Attached to legs with bearings
Cone made of steel alloy
Nickel & molybdenum added to
increase hardness & heat
resistance
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Elements of Roller Cone Bit
• Chromium, silicon & cobalt also used
• Cones heat treated
– Carburizing: Heating steel in carbon-rich
atmosphere. Outer layer absorbs carbon &
forms a tougher outer shell
– Heating & quenching : hot carburized steel
immersed in liquid to cool fast. Carbon atoms
trapped between iron atoms. It makes steel
harder but more brittle
– Tempering : reheating to a lower temp than
above. Prevents cracks from forming due to the
stresses that quenching causes. Also restores
steel’s impact strength
Drilling and Well Completion – Dr. Abhay Sharma
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Drilling Bits
Elements of Roller Cone Bit
• Cones are designated by Journal angle
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Elements of Roller Cone Bit
On- Centre Cone Alignment
• Centre axis of all cones meet at
bit axis
• Cones rotate around a common
center of axis
• Cutters have straight-on contact
with formation
• WOB forces cutters into the
rock
Drilling and Well Completion – Dr. Abhay Sharma
7
Drilling Bits
Elements of Roller Cone Bit
Off- Centre Cone Alignment
• Centre axis of cones do not meet at
bit axis
• Horizontal distance between bit axis
& cone axis is called bit offset
• Cutters do not rotate around a
common centre as bit rotates
• Offset causes cutter tips to drag or
scrape across the formation as WOB
& RPM is applied. Acts like shovel
(Scraping & Gouging Action)
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Elements of Roller Cone Bit
Cutting Element : Steel-Tooth Cutters
• Long & widely spaced teeth : soft formations
• Medium height & less widely spaced teeth :
medium hard formations
• Shorter & closely spaced teeth :
hard formations
• Tungsten carbide may be applied to teeth for
wear resistance in hard formations
• Self-sharpening feature if applied on one side
only
Drilling and Well Completion – Dr. Abhay Sharma
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Drilling Bits
Elements of Roller Cone Bit
Cutting Element : Tungsten Carbide Inserts
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Elements of Roller Cone Bit
• Fluid circulation
•Nozzles provide jet velocity
•Hole cleaning
•Bit cooling
•Made of tungsten carbide
•Bits normally have 3 but may have 4
nozzles
•Nozzles are replaceable
Drilling and Well Completion – Dr. Abhay Sharma
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Drilling Bits
Elements of Roller Cone Bit
• Fluid circulation
•Large size bits for soft formations
may have extended nozzles
•Nozzles are near the bit bottom
•Deliver more hydraulic power to
the bottom as less dissipation of
energy
•Prevents balling of the bit by
cleaning the cuttings the better
way
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Roller Bit Classification Chart
Drilling and Well Completion – Dr. Abhay Sharma
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Roller Bit Classification Chart Drilling Bits
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Roller Bit Classification
• 4 digit code
• First three are numeric, Fourth is alphabetic
• First digit is about formation
• Second digit tells relative hardness
• Third digit tells about bearing & gauge
protection
• Fourth digit tells special feature
Drilling and Well Completion – Dr. Abhay Sharma
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Drilling Bits
Roller Bit Classification : First Digit
First digit code from 1 to 8
1 to 3 are for steel-tooth bits
1: Soft formation steel-tooth bits
2: Medium to medium hard formation steel- tooth bits
3: Hard formation steel-tooth bits
4 to 8 are for insert bits
4: Soft formation insert bits
5: Soft to medium formation insert bits
6: Medium-hard formation insert bits
7: Hard formation insert bits
8: Extremely hard formation insert bits
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Roller Bit Classification : Second Digit
Any number between 1 to 4
Tells relative hardness in that category
1 is softest & 4 is hardest
Roller Bit Classification : Third Digit
Numbered between 1 to 7, 8 & 9 reserved for future use
1 : Standard roller brg. (open/non-sealed)
2 : Standard roller brg. (air cooled)
3 : Standard roller brg. (open/non-sealed) with gauge
protection
4 : Sealed roller brg.
5 : Sealed roller brg. with gauge protection
6 : Sealed journal bearing
7 : Sealed journal brg. Drilling
withandgauge protection
Well Completion – Dr. Abhay Sharma
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Drilling Bits
Roller Bit Classification : Fourth Digit
16 alphabets
A : Air application
B : Special brg. Seals
C : Centre nozzle
D : Deviation Control
E : Extended full length nozzles
G : Special & additional gauge & body protection
H : Horz. Or steering application
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Roller Bit Classification : Fourth Digit
J : Jet deflection
L : Lug pads
M : Motor application
S : Standard steel tooth application
T : Two roller cone
W : Enhanced cutting structure
X : Predominantly chisel inserts
Y : Conical inserts
Z : Other shape inserts
Drilling and Well Completion – Dr. Abhay Sharma
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Drilling Bits
Dull Bit Grading :How much bit life used &
how much balance
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Dull Bit Grading :
Cone Dragging or Skidding (CD)
Cracked Cone (CC)
Drilling and Well Completion – Dr. Abhay Sharma
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Drilling Bits
Dull Bit Grading :
Inner Cutter wear
Flat-crested Wear (FC)
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Dull Bit Grading :
Junk Damage
Washed Out Bit
Drilling and Well Completion – Dr. Abhay Sharma
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Drilling Bits
Diamond Bits Profile
• Cutters
• Body
• Shank
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Diamond Bits Profile
• Cutters
• Body
• Shank
Drilling and Well Completion – Dr. Abhay Sharma
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Diamond Qualities
• Best compressive strength & modulus of
elasticity
– If force applied gradually, it will not break
easily until load applied is very high
– Diamond will rather deform under load & gain
its shape & size once load is removed
• Best thermal conductivity of any material
• Heat flow very quick
• Can transmit heat generated by drilling to drilling
fluid as fast as drilling fluid can absorb it
• So diamond is as cool as the fluid
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Diamond Bit Classification
Drilling and Well Completion – Dr. Abhay Sharma
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Drilling Bits
Diamond Bit Classification
BIT Profile:
Flat or shallow : evenly distributes
the WOB ; limited rotational
stability and uneven wear.
Taper or double cone : allows
increased distribution of the
cutters toward the O.D.; greater
rotational and directional stability
and even wear
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Diamond Bit Classification
BIT Profile:
The parabolic profile provides a
smooth loading over the bit
profile and the largest surface
contact area. This bit profile
therefore provides even greater
rotational and directional stability
and even wear. This profile is
typically used for motor or
turbine drilling.
Drilling and Well Completion – Dr. Abhay Sharma
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Drilling Bits
Diamond Bit Classification
BIT Profile
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Diamond Bit Classification
Hydraulic Design
Drilling and Well Completion – Dr. Abhay Sharma
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Drilling Bits
Diamond Bit hydraulics
• No nozzles
• Outlet for drilling fluid in the centre
• Outlet leads flow into the channels cut into the matrix body
• Fluid flows across the face of the bit
• Purpose
– Clean the bit
– Cool the bit
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Diamond Bit hydraulics :Radial Flow
Mud flows out from crow’s foot openings
into water courses radially outwards
from centre
May be parallel or expanding channels &
may become shallower
These variations control fluid velocity
across bit face that control cleaning &
cooling
Removes greatest quantity of cuttings
That is imp when ROP is faster in soft-
medium formations
Suitable for larger stones in soft-medium
formations as they are easy to clean &
cool as distance between matrix &
diamond top is greater
Drilling and Well Completion – Dr. Abhay Sharma
20
Drilling Bits
Diamond Bit hydraulics Cross Flow
Similar outwardly going radial
channels called feeders
Also has secondary channels called
collectors
Collectors not connected to feeders or
crow’s feet
V-shaped & start near the gauge &
quickly widen
Creates low pr in collector area that
sucks fluid from feeders across the
top of the diamonds
Fluid moving directly over the
diamonds is called cross-pad flow
Better cooling
Better for hard & abrasive formations
Drilling and Well Completion – Dr. Abhay Sharma
Drilling Bits
Diamond Bit : Cutter Size and Density
Drilling and Well Completion – Dr. Abhay Sharma
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