3. Selecting Ideal Bit
• Drilling Cost per foot
• Drillability
• Abrasiveness
• Type of Reservoir
• Cost of the Bit
• Depth
4. Improving Bit Performance
• Stabilize the Bit
• Maintain minimum mud weight, sand & solids
• Maintain adequate bottom hole cleaning
• Protect the seals - avoid pressure surges
• Thoroughly inspect bit before re-running
• Keep oil from the mud, and from the seals
• Follow manufacturers recommendations (e.g. 6,000
lb/in of diameter and 40-60 RPM)
6. DRILL BITS
TYPES OF DRILL BITS-
Detachable bits- Removable from the drill when required.
Forged bits- Made up of single length of drill steel and are available at
several shapes.
7. Bits
• Types of Bit
• Drag Bit
• Roller Cutter Bit
• Drill Bit Classification
• Drag Bit Classification
• Roller Cutter Bit Classification
• Drill Bit Grading
• Tooth Wear/Loss
• Bearing Wear
• Gauge Wear
8. Contd.
A steel-toothed piece of equipment attached to the lower
end of the drillstring in order to:
• crush,
• scrape and,
• grind
formation loose.
The two types available are:
• drag bits
• rolling cutter bits
9. Drag bit
• They consist of fixed cutter blades that are integral with the body of the bit and
rotate as a unit with the drillstring. The cutting element consists of steelcutters,
diamond, or polycrystalline diamond compact (PDC).
• Steelcutter bits the serrated steel blades are set at different angles(e.g. a fishtail
bit).
• Natural diamond bits the face or crown of the bit consists of many diamonds set in
a tungsten carbide matrix.
• Polycrystalline diamond compact (PDC) bits a layer of synthetic PDC is bonded to a
cemented tungsten carbide, it contains many diamond crystals bonded together.
The sintered PDC compact is bonded either to a tungsten carbide bit-body matrix
or to a tungsten carbide stud that is mounted in a steel bit.
• Thermally stable polycrystalline (TSP) bits these bits are manufactured in a similar
fashion to PDC bits but are tolerant of much higher temperatures than PDC bits.
10. Roller Cutter Bits
• They have two or more cones containing the
cutting elements which rotate about the axis of
the cone as the bit is rotated at the bottom of the
hole. The 3-cone rolling cutter bit is by far the
most common.
• Important factors to consider in this type of bit
are: structural materials, bearing-seal-lubricating
design, cutting structure arrangements, and
hydraulic arrangements.
11. Types of Bits
1. Drag Bits: Fixed cutter blades
Consist of fixed cutter blades that are
integral with the body of the bit and rotate
as a unit with the drill string (19th century).
2. Rolling Cutter Bits: Rock bits - with cones
(1909) have two or more cones containing the
cutting elements which rotate about the axis
of the cone as the bit is rotated at the
bottom of the hole.
12. Drag Bits
• Design Features
– Number & shape of cutting blades/stones
– Size and location of the water courses
– Metallurgy of the bit and cutting elements
13. Drag Bits
– Drilling is achieved by physically blowing cuttings from
the bottom of the bore-hole
14. Drag Bits
Advantages
– No rolling parts which require strong clean bearing
surfaces
– Because it is made from one solid piece of steel
there is less chance of bit breakage, which would
leave junk in the bottom of the hole
18. • Best for
– Soft formations
– Uniform formations
– unconsolidated formations
• Now, replaced by other types in all area
Steel Cutter Bits
19. When Using Natural Diamond Bit?
• Penetration rate of rock bit < 10 ft/hr
• Hole diameter < 6 inches
• When it is important to keep the bit and pipe in
the hole
• When bad weather precludes making trips
• When starting a side-tracked hole
• When coring
• When a lower cost/ft would result
20. – Best for hard non-brittle formations
– The face or crown of the bit consists of many
diamonds set in a tungsten carbide matrix
– Fluid courses are provided in the matrix to direct
the flow of drilling fluid over the face of the bit.
Diamond Bits
21. • Shape of crown profit:
– Step type
– Long taper (straight hole, high wt.)
– Short taper (easier to clean)
– Non taper (directional drilling)
Diamond Bits
22. • Size and number of diamonds, depend on the
hardness of the formation
– Hard formations:
• Many small stones
• 0.07-0.125 carrot
– Soft formations:
• Few large stones
• 0.75-2.0 carrot
Diamond Bits
23. • Pressure drop across the face of the bit
• Pump pressure measured with the bit off bottom-
pump pressure with the bit drilling = 500 : 1000 psi
• Manufacturer usually provide estimate of approximate
circulating rate required establishing the needed
pressure drop across the bit.
Diamond Bits
30. PolyCrystalline Diamond (PCD) Bits
• Since mid 1970’s a PDC Bits has been made possible by
the introduction of a sintered polycrystalline diamond
drill blanks, as a bit cutter element
• The drill blanks consist of a layer of a synthetic
polycrystalline diamond about 1/64 in. thick that is
bonded to a cemented tungsten carbide substrate in a
high-pressure high-temperature (HPHT) process
32. PolyCrystalline Diamond (PCD) Bits
• It contains many small diamond crystals bonded
together
• The PCD is bonded either to a tungsten carbide bit-
body matrix or to a tungsten carbide stud that is
mounted in a steel bit body
• They perform best in soft, firm, and medium-hard,
non-abrasion formations (not gummy)
33. PolyCrystalline Diamond (PCD) Bits
• Good results are obtained in carbonates or evaporates
that are not broken up with hard shale stringers.
• Also good in a sandstone, siltstone, shale
• Design of crown profile is important, double-cone and
flat profile
• Size, shape, number of cutters and angle of attack back
rake, side rake and exposure
34. PolyCrystalline Diamond (PCD) Bits
• Advantages:
– Increase penetration rates in oil & gas wells
– Reduce drilling time and costs
– Cost 5-15 times more than roller cone bits
– 1.5 times faster than those 2 years earlier
– Work better in oil based muds; however, these
areas are strictly regulated
35. Relative Costs of Bits
Diamond WC Insert Milled
Bits Bits Tooth Bits
$/Bit
• Diamond bits typically cost several times as much as tri-cone
bits with tungsten carbide inserts (same bit diam.)
• A TCI bit may cost several times as much as a
milled tooth bit.
36. Grading of Worn PDC Bits
CT - Chipped Cutter
Less than 1/3 of cutting element
is gone
BT - Broken Cutter
More than 1/3 of cutting element is
broken to the substrate
37. Grading of Worn PDC Bits – cont’d
LT - Lost Cutter
Bit is missing one or more
cutters
LN - Lost Nozzle
Bit is missing one or more
nozzles
40. 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
42. 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)
43. 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
44. Classification of Tricone Bits
(a)Milled tooth cutters
(b)Tungsten 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)
46. 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
47. 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
48. Fluid flow through water courses in bit
Proper
bottomhole
cleaning is very
important
50. 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
52. 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
56. 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
57. Grading of Dull Bits
How do bits wear out?
• Tooth wear or loss
• Worn bearings
• Gauge wear
58. Grading of Dull Bits
How 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
59. 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
60. 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
61. Grading of Dull Bits
How do bits fail?
Washed out Bit Lost Cone
62. Grading of Dull Bits
How do bits wear out?
• Gauge Wear:
• Bit is either in-Gauge or out-of-Gauge
• Measure wear on diameter (in inches),
using a gauge ring
BIT
GAUGE RING
63. Thank you for ur kind attention
• Email me at
Jyotikhatiwadaanischit@gmail.com
Jyoti Anischit
TU EGEO, 2nd semester
Roll no. 12
