This document discusses drill bits used in oil and gas drilling. It describes the main types of drill bits including roller cone bits, natural diamond bits, PDC bits, and TSP bits. It explains how each type of bit cuts rock through different mechanisms like compression, grinding, or shearing. The document also provides details on bit design factors for both roller cone bits and PDC bits, including bearing assembly design, cutter design, nozzle placement, and more. It covers how to select the proper bit based on formation hardness and classify bits using the IADC system. Performance factors like WOB, RPM, mud properties, and hydraulic efficiency that influence bit performance are also summarized.

1. SARWAR ALAM ANSARI
MS-Petroleum Engineering ( Student)
SARWAR ALAM ANSARI
MS-Petroleum Engineering
Khazar University, Baku, Azerbaijan
DRILL BITS

2. CONTENTS
INTRODUCTION
TYPES OF DRILLING BIT
BIT DESIGN
 BIT SELECTION
 ROCK BIT EVALUATION
 BIT PERFORMANCE

3. INTRODUCTION
 Drilling by compression, crushing, ploughing, grinding and
shearing the rock
 Bits are varied in design
 The performance of the bit is a function of several parameters
 WOB (Weight on bit)
 RPM (Rotation per minute)
 Mud properties
 Hydraulic efficiency
 When bit has drilled a section the damage is recorded using
Dull Bit Grading System

4. TYPES OF DRILLING BIT
Fixed Cutter Roller Cone
Drill Bits
PDC Diamond Mill tooth Insert
Roller BearingTSPNatural Diamond Impreg Friction Bearing

5. NATURAL DIAMOND BIT:
PLOUGHING/GRINDING
PDC BIT:
SHEARING
F
ROLLER CONE BITS:
COMPRESSION/CRUSHING
F

6. TYPES OF DRILLING BIT
Drag Bits:
First bits used in rotary drilling
 Not used in industry today
 Limited to drilling through uniformly, soft,
unconsolidated formations where there were
no hard abrasive layers.
Roller Cone Bits:
 Drills by compression & crushing action
 First rollers consisted of 2 cones, but they weren’t
successful due to balling of cones with formation
 Cones are mounted on bearing pins which extend
from body
 Bearings allow cones to rotate around own axis.
 Steel Tooth type
 Tungsten Carbide inserts

7. TYPES OF DRILLING BIT
Natural Diamond Bits
 Cuts by ploughing & grinding
 Drilling of hard rock and longer sections
 Diamonds are bonded on surface of material
 Sensitive to shock and vibration
 Very costly (10 times more expensive)
 Slower ROP than Roller Cones
 Last longer than Roller cones since no moving parts
Formation
Diamond
Ploughing /
Gridning

8. TYPES OF DRILLING BIT
PDC (Polycrystalline Diamond Compact) Bits:
 Cuts by Scraping
 Introduced in 1980s
 Use small discs of synthetic diamond
 High ROPs
 Most widely used in industry today
TSP (Thermally stable Polycrystalline)
 Similar to PDC
 Tolerant to much higher temperatures
Formation
PDC
Shearing

9. BIT DESIGN
Roller Cone Bit Design:
1. Bearing assemblies
2. Cone design
3. Cutting elements
4. Fluid circulation

10. BIT DESIGN
Bearing assembly:
 Cones are mounted on bearings
 Three Types of bearing assembly
 Roller Bearings – help to support radial
loading (WOB)
 Ball bearings – resist longitudinal or thrust loads
 Friction bearings – in the nose assembly,
helps to support radial loading
 Bearings must be made from toughened steel by
heat treatment
 Most important factor is space availability
 Ideally Bearing should be large enough to
support applied loading
 Bearing size is balanced with strength of the
journal (journal diameter) and strength of
cone shell (shell thickness)

11. BIT DESIGN
Details of Bearing Structure:

12. BIT DESIGN
Types of bearing assemblies:
Sealed Bearing assembly Journal Bearing assembly

13. BIT DESIGN
Cone Design:
 Cone design is largely determined by
 Journal (or pin) angle
 Cone slippage effect (not even rotation
effect) – rock is drilled by grinding +
scraping action
 Magnitude of JA affects the size of the cone
 If journal angle increases then size of the cone
decreases
 If journal angle decreases then sized of the
cone increases
 Cone slippage is achieved by
 Design of cones (inner cone gouges,
heel scrapesthe rock)
 Offsetting axes of the cones (offset
journals away from the center

14. BIT DESIGN
The journal angle is the angle at which the journal is
mounted, relative to a horizontal plane.
Formation
Characteristics
Insert/Tooth
Spacing
Insert/Tooth
Properties
Penetration
Drill cut Gen.
Cleaning Flow
Requirements
Soft Wide Long & Sharp High High
Intermediate Relatively
Wide
Shorter &
Stubbier
Relatively High Relatively High
Hard Close Short &
Rounded
Relatively Low Relatively Low
Journal Angle 33 34 - 36 39
Type of formation Soft Medium Hard
 Cone offset:
Soft formation: 0.5 and 0.375 in
Hard formation: 0.0325 and 0.0 in

15. BIT DESIGN
Cutting Elements:
 Selection is based on hardness of formation to be drilled
 Main consideration depend on hardness of formation
 Type of cutter (Steel or Tungsten Carbide inserts)
 Geometry of cutters (Height, spacing)
 Soft formations need long, thin, widely spread teeth to prevent
bit balling
 Moderately hard formations have shorter, wider teeth for
withstanding heavier loads, wide spread to allow cleaning
 Hard formations have shortest and stubbier. Spread of cutters is
less important due to low ROP and small cuttings sizes
 Cutter elements are covered with tungsten carbide element to
increase its wear resistance

16. BIT DESIGN
Fluid circulation:
 Original bit design allowed fluid
circulation through the middle of the
bit led to build up of cuttings of the
face of the bit
 More efficient way of cleaning face of
bit was then introduced circulation
through nozzles
 Jet nozzles are available in many
sizes
 Made of tungsten carbide to
prevent fluid erosion
 Size of nozzle refers to inner
diameter of the ring
 Outside diameter is the same so that it
can fit to any size of the bit

17. BIT DESIGN
PDC Bit Design:
 Major components of PDC bit design are:
 Bit body material
 Bit profile
 Cutting material
 Cutter rake
 Cutter density
 Cutter exposure
 Cutter size
 Fluid circulation

18. BIT DESIGN
Cutter material PDC :
 (PCD) Polycrystalline diamond
– synthetic material with 90 - 95%
pure diamond and manufactured
into compacts
 PCD is formed in 2 stages
HPHT process:
1. Manufacture artificial diamond
crystals by exposing graphite to
high pressures (600,000 psi) in
presence of other chemicals
2. Sintering of diamond powder
with catalyst/binder in
>1400ºC, 750,000 psi
 Disc cutters and Stud cutters

19. BIT DESIGN
Cutter material TSP :
 PDC cutters were chipped while drilling due to internal
stresses caused by differential expansion of diamond and
binder material (Cobalt)
 Thermal coefficient of expansion of binder = 1.2 x 10-5
 Thermal coefficient of expansion of diamond = 2.7 x 10-6
 Cobalt expands faster, stresses develop due to different
rates of expansion
 In TSP cutters binder material is removed by leaching
with acids to improve stability at higher temperatures
 Absence of binder material make is impossible to bond
TSP to Tungsten carbide substrate
 Strength of PCD material and substrate is weaker
 TSP are smaller size and should be set in matrix of the bit

20. BIT DESIGN
Bit Body Material :
 Two types of bit body material
 Steel shell
 TC (tungsten carbide) shell on steel body
 Steel body bits
 Uses stud cutters (can be removed and replaced
without damage to bit body, no need for braze)
 Face erosion is problem (use hard facing)
 Broken cutters due to limited impact resistance
(no support of cutters)
 Matrix body bits
 Disc cutters are used in the body
 Resistant to abrasion and erosion
 Impact resistance for cutter is provided
 More expensive

21. BIT DESIGN
Cutter Rake (back rake and side rake):
Back rake – angle between face of
cutter and formation (12º to 40º)
 Angle determines the aggressiveness of the cutters (ROP*, size of
cutting that is produced, wear, torque)
 Smaller the rake angle – more aggressive is the bit (high ROP, bigger
cutting, high wear, more torque) as cutters take more depth of cut
 Opposite is true for big rake angles
Side rake – orientation of the cutter from left to right (usually is small
 Assist hole cleaning my mechanically directing cutting toward
annulus

22. BIT DESIGN
Bit Profile:
Three types of PDC bit crown profile
 Flat or shallow cone (evenly distributes WOB among each of
cutters, limited rotational stability, uneven wear)
 Tapered or double cone (cutters distributed towards OD, even
wear, greater rotational and directional stability)
 Parabolic (smooth loading of the bit profile, even greater
rotational and directional capability, even wear)

23. BIT DESIGN
Bit Length:
 Shorter bits are more steerable
 2 bits on the left are for side-track
 Third bit is for general directional work

24. BIT DESIGN
Cutters density:
 Number of cutters on bit
surface per unit area
 Generally speaking, the
harder the formation, the
higher the cutter count
required
 High cutter count means that
the load is shared across more
cutters and therefore each cutter
achieves a lower depth of cut
(lower ROP)
 More cutters makes bit
more durable
 If high density is used cutters
should be small enough to
clean the surface of the bit

25. BIT DESIGN
Cutters size:
 PDC cutters are usually
available in 8, 11, 13, 16, 19
and 22mm diameters.
 13 mm cutters are the most
common
 Increased cutter size means
increased torque, increased
ROP, decreased durability
 8, 11 – hard rock,
extended durability
 13, 16 – medium hard
formations, medium
durability
 19, 22 – high ROP, less
durable, high frictional heat

26. BIT DESIGN
Cutters exposure:
 Amount by which the cutters protrude from the bit body.
 High exposure - to ensure good cleaning of cleaning bit face
 Lower exposure – good support of the cutters on bit body

27. BIT DESIGN
Cutter Types:
 Reed Hycalog: T-Rex and Raptor
 Smith: GeoMax, SonicMax, GridMax, TecMax Quick
Cutter, Arrow Cutter
 Hughes Christensen: Zenith, ZPlus
 Security DBS: ERC, ESDRC, CRC, Z3

28. BIT DESIGN
Fluid circulation:
 Must be designed to remove the cuttings efficiently and
cool the bit surface
 Design of water courses that run across the bit area
 Usually 9 jets are available on PDC bits
Hydraulic evaluation of bits for
cutting structure cleaning and
junk slot flow, where fluid and
cuttings are efficiently moving
away from the hole bottom.

29. BIT DESIGN
Bit Selection:
 IADC developed comparison charts for different bits for
classifying bits according to their characteristics and
application
 Two systems: Roller Cones and Fixed cutter bits
 Bits are classified according to IADC codes
 The position of each bit is defined by three numbers and one
character
 Numbers sequence define “Series, Type and Features” of the
bit
 Additional character defines additional design features

31. BIT DESIGN
Formations characterization:
Soft
 Unconsolidated clays and sands
 Low WOB 3000-5000 lbs/in of bit diameter
 High RPMs (120-250)
Medium Formations
 Shales, Gypsum, Sands, Siltstones
 Low WOB 3000-6000 lbs/in bit diameter
 High RPMs (120-250), chalk required less RPM
Hard formations
 Limestone, Anhydrite, Hard sandstone, Dolomite
 High compressive strength, abrasive material
 High WOB 6000-10000 lbs/in of bit diameter
 Slow RPMs (40-100) to help grinding, crushing

32. BIT DESIGN
PDC bit classification:

33. BIT DESIGN
IADC Dull bit grading:

34. BIT DESIGN
Bit performance:
 Performance determined in
 How much the bit drilled (ft)
 How fast it drilled
 How much it cost per foot of hole drilled
 Compare one bit with another after well is drilled
 Bit performance is function of
 WOB (Weight on bit)
 RPM (revolutions per minute)
 Mud properties (Static &
Dynamic chip hold down effects)
 Hydraulic efficiency

35. BIT DESIGN
Performance of roller cone bits (ROP):
 Weight on bit (WOB) required to
overcome compressibility of
formation
 Limitations on WOB are
 HHP (Hydraulic horse power)
– if there is no enough
Hydraulic horsepower at the
bit then applying more WOB
will not help
 HHP can be increased either
by smaller nozzles sizes or
increasing the flow rate

36. BIT DESIGN
Weight on bit:
 Type of formations-WOB is
limited in soft formations –
excessive weight will bury the
teeth of bit
 Hole deviation – bending (or
buckling) might happen if too
much weight is applied
 Bearing life – greater the load,
the less operational life of
bearings
 Tooth life – in hard formations
excessive WOB may cause
teeth to break

37. BIT DESIGN
Revolutions per minute (RPM)
 ROP varies with RPM for
different formations strength
 Applied RPM depends on
 Type of bit – lower RPMs
are used for insert bits
compared to milled tooth
bits.
 Type of formation – hard
formations are less easily
penetrated and so required
low RPMs. High RPM may
cause damage to the bit

38. BIT DESIGN
Mud properties:
 Hydrostatic pressure provides overbalance for keeping formation fluids in rock
 Mud cake is formed when fluid invades pores (sand, carbonates)
 Overbalance and mud cake affect the removal of cuttings
 Static chip hole down – differential pressure holds the chip on bottom in
permeable formations due to inability of fluid penetrate into the crack
 Dynamics chip hold down – pressure drop when mud flows into cracks in
less permeable formations
 Prevent chip hold down effect reducing the overbalance (lowering MW) and
improving solids control
 Theoretical approach as there are many other factors: time for formation of filter
cake, scraping action of the cutters, jet flow from nozzles, bit vibration etc.