06.TBT1 Drilling Bits

Introduction to Drilling Technology
Dr. Javier Holzmann
SS 2018
Introduction to Drilling Technology
Introduction to Rotary-Drilling Technology
Drilling a Well, Drilling methods
Rock Mechanics, Well stability, Overbalance vs. Underbalance
Borehole Hydraulics
Drilling Mud: Functions, Properties, Rheology
Drilling Bits, Bit Selection Criteria
Drilling Optimization Concepts
Drill-string Basics
Downhole Motors I (Theory, Moineau Motors)
Downhole Motors II (Turbines, Selection Criteria)
Special Drilling Systems (Drilling Hammer, Coring)
Formation Pressure, Frac Gradient
Measuring drilling parameters
Dr. Javier Holzmann

Institut für Erdöl- und Erdgastechnik TBT I_SS 2018 2
What you will learn
 Drill bit requirements, types & costs

 Roller Cone bit design
 PDC bit design
 Selection & classification of Roller Cone bits
 Bit wear out including examples
 Grading of dull bits
 How to improve bit performance
 Improving bit life
Dr. Javier Holzmann

The Drilling Bit
 Cutting or boring tool which is made up on the end of
the drill string
 Drills through the rock by scraping, chipping, gouging
or grinding the rock at the bottom of the hole
 Drilling fluid is circulated through passageways in the
bit to remove the drilled cuttings
 Bit selected for a particular application depends on
formation type
Dr. Javier Holzmann

The Drilling Bit
 Bit performance is a function of several operating

parameters:
- Weight on bit (WOB)

- Rotations per minute (RPM)
- Mud properties
- Hydraulic efficiency
Dr. Javier Holzmann

The Ideal Bit
 Low cost per foot drilled
. 1. High drilling rate
2. Long life
3. Drill full-gauge, straight hole
4. Moderate cost
Dr. Javier Holzmann

The Ideal Bit
 Low cost per foot drilled

 “The Ideal Bit” depends on the type of formation to
be drilled:
- Hardness (soft, medium, hard)
- Abrasiveness
- Cuttings stickiness
- Other considerations, i.e. costs
Dr. Javier Holzmann

Bit Types
 Drag Bits
 Roller Cone Bits
 Diamond Bits
Drag Bit Roller Cone Bit Diamond Bit

(Rock Bit)
Dr. Javier Holzmann Source: Heriot-Watt University, Institute of Petroleum Engineering;
Institut für Erdöl- und Erdgastechnik (Courtesy of Hughes Christensen) TBT I_SS 2018 8
Relative Costs of Bits
$/Bit
Diamond bits TC Insert bits Milled Tooth bits
 Diamond bits typically cost several times as much as tri-cone

bits with tungsten carbide inserts (same bit diameter)
 TCI bits may cost several times as much as milled tooth bits
Dr. Javier Holzmann

Drag Bits
 First bits used in rotary drilling

 No longer in common use
 Consist of rigid steel blades that rotate as a single unit
 The simple designs were used to successfully drill
through soft formations until 1900
 Then bit performance was greatly improved by the
introduction of hard facing the blade’s surface &
design of fluid passageways
 Dragging/scraping action requires high RPM and low
WOB
Dr. Javier Holzmann
Drag Bits
 Decline in use due to:

- Introduction of roller cone bits, which could drill soft
formations more efficiently
- If too much WOB was applied excessive torque led to bit

or drill pipe failure
- Tend to drill crooked hole  deviation control necessary
- Limited to drill through uniformly, soft, unconsolidated

formations without hard abrasive layers.
Dr. Javier Holzmann

Roller Cone Bits (or Rock Bits)
 Most common type of bit world wide

 Cutting action provided by cones
having either steel teeth or tungsten
carbide inserts
 Cones rotate on bottom of the hole and drill hole

mostly with a grinding and chipping action
 Classified as milled tooth or insert bits

Note: (TCI = Tungsten Carbide Insert Bit)
Dr. Javier Holzmann

Milled tooth bit Insert bit
Dr. Javier Holzmann Source: Heriot-Watt University, Institute of Petroleum Engineering;

Institut für Erdöl- und Erdgastechnik (Courtesy of Hughes Christensen) TBT I_SS 2018 13
Roller Cone Bits
23” 17”
Milled Insert
Tooth Tooth
4 3/4” 4 3/4”
Dr. Javier Holzmann Source: Teodoriu, C.: Script Tbt 1, 2014

Institut für Erdöl- und Erdgastechnik Courtesy Smith Bits TBT I_SS 2018 14
Source: http://petroleumsupport.com/wp-content/uploads/2012/10/Elements-of-a-rock-bit.jpg
Dr. Javier Holzmann
Roller Cone Bit - General Nomenclature
Source: Petroleum Engineering Handbook, Ed. Lake, L. W. and Mitchell, R.F, SPE, USA, 2006
Dr. Javier Holzmann
 First roller cone bit introduced in 1909
by Howard Hughes:
- major innovation, rotary drilling was extended
to hard formations.
- Not self-cleaning 2-cone bit which frequently
balled up since the teeth on the cones did not mesh
 introduction of a 3-cone bit with meshing teeth in the
1930s which is still in use today
- Cones mounted on bearing pins or arm journals, bearings allow
each cone to turn about its own axis as bit is rotated.
- The 3 cones allow even weight distribution, balanced cutting
structure and drill a better gauge hole than 2-cone design
Source: Teodoriu, C.: Script Tbt 1, 2014
Dr. Javier Holzmann
 The major advances in rock bit design:

+ Improved cleaning action by using jet nozzles
+ Using tungsten carbide for hard facing and gauge
protection
+ Introduction of sealed bearings to prevent the mud
causing premature failure due to abrasion and
corrosion of the bearings.
Dr. Javier Holzmann

Cutting Actions for Roller Cone Bits
Dr. Javier Holzmann
Action of Roller Cutter Bit
on Rock Surface
E
Dr. Javier Holzmann

Institut für Erdöl- und Erdgastechnik Source: Teodoriu, C.: Script Tbt 1, 2014 TBT I_SS 2018 20
Diamond Bits
 Cutting material: diamond

- Great hardness and wear resistance
 Today natural diamonds are mostly

replaced by industrial diamonds
 Type of drag bit; no moving cones,

operates as a single unit
 Cutting action achieved by scraping away the rock
Dr. Javier Holzmann

Diamond Bits
 Despite its high wear resistance diamond is sensitive
to shock and vibration
 Effective fluid circulation across bit face necessary to
prevent bit from overheating and avoid bit face to
become smeared with the rock cuttings (bit balling)
 Disadvantages:
- High costs - sometimes 10 times more expensive than
similar sized rock bit
- Guarantee of higher ROP than correctly selected roller
cone bit in the same formation is not given
Dr. Javier Holzmann

Diamond Bits
 Advantages:
+ Cost effective when drilling formations where long
rotating hours (200-300 hours per bit) are required
+ No moving parts  last normally longer than roller cone
bits and may be used for extremely long bit runs
 Number of round trips reduced
 Lower capital bit cost
- Important in areas with operating costs are high (i.e.
offshore drilling)
+ Diamonds of used bits can be extracted & reutilized
Dr. Javier Holzmann

Diamond Bits - PDC Bits
 PDC = polycrystalline diamond compact
 Natural diamonds replaced by small discs of synthetic
diamonds
 Introduced in the 1980’s & run sucessfully since then
 Same advantages and disadvantages as natural diamond
bits
 Advantages:
+ Discs can be produced in any size and shape and are
insensitive to failure
+ Very successful in operations with long bit runs & high ROP or
when run in combination with “turbodrills” and oil based mud
Dr. Javier Holzmann

Diamond Bits - PDC Bits
Source: Heriot-Watt University, Institute of Petroleum Engineering;

Dr. Javier Holzmann (Courtesy of Hughes Christensen)
Diamond Core Bit
Nomenclature

Institut für Erdöl- und Erdgastechnik Courtesy Hughes Christensen TBT I_SS 2018 26
PDC Bit Nomenclature
Source: Strata Bit Corporation, 600 Kenrick, Suite A-1, Houston, TX 77060, USA;
Dr. Javier Holzmann Courtesy Strata Bit Corp.
Diamond Bits - TSP Bits
 TSP = Thermally Stable Polycrystalline (TSP)
 Introduced in the late 1980’s
 Manufactured similarly to PDC bits but can withstand

much higher temperatures than normal PDC bits
Dr. Javier Holzmann

Different Bit Types
PDC bit TCI bit Milled Tooth bit

Dr. Javier Holzmann Source: Petroleum Engineering Handbook, Ed. Lake,
Institut für Erdöl- und Erdgastechnik L. W. and Mitchell, R.F, SPE, USA, 2006 TBT I_SS 2018 29
Bit Design
 Roller Cone Bit Design

- Bearing assemblies - Cutting elements
- Cones - Fluid circulation
 PDC Bit Design

- Bit body material - Cutter exposure
- Cutter rake - Fluid circulation
- Bit profile - Cutter density
Dr. Javier Holzmann

Roller Cone Bit Design
 Bearing assemblies
 Cones
 Cutting elements
 Fluid circulation
Dr. Javier Holzmann

Types of Bearings
 Roller bearings
- Linear contact
- Form outer assembly and help to support
the radial loading (WOB)
 Ball bearings
- Point contact
- Resist longitudinal or thrust loads and
help to secure the cones on the journals
 Journal (or friction) bearings
- Surface contact
- In the nose assembly, help to support
radial loading
Dr. Javier Holzmann

Bearing Assemblies
 The cones of a roller cone bit are mounted on journals
Source: Heriot-Watt University, Institute of Petroleum Engineering

Dr. Javier Holzmann
Bearing Assemblies
 Exploded view of seal and bearing components
Dr. Javier Holzmann
Bearing Assemblies
 Comparison of journal and roller bearing arrangements
Dr. Javier Holzmann
Bearing Assemblies
 Typical roller bearing arrangement

Bearing Assemblies
 Typical journal bearing arrangement

Bearing Assemblies
 Bearing material made of toughened steel

- Need to withstand any chipping and breaking under
massive loads they are exposed to
 Most important: space availability
- Large enough to support the applied loading, but balanced
against the strength of journal and cone shell
 Final design = compromise:
- Bearings should not wear out before cutting structure
 All bit components should wear out evenly
Dr. Javier Holzmann

Bearing Assemblies
 First bearing assemblies

open to drilling fluid
 Introduction of sealed
bearing bits in the late
1950s to extend bearing
life
 Sealing serves as protection from abrasive solids in mud
which would cause excessive frictional resistance in the
bearings
 Bearings have to be lubricated
Dr. Javier Holzmann
Bearing Assemblies
 Journal bearing bits do
not have roller bearings,
cones are directly
mounted onto journal
 Advantage of a larger
contact area over which
load is transmitted from the cone to journal
 Contact area specially treated and inlaid with alloys to
increase wear resistance
 Only little lubrication required
Dr. Javier Holzmann
Lubrication type
 Dry lubrication
 Mud lubrication
 Grease lubrication
Dr. Javier Holzmann

Lubrication System
 Typical roller cone

bit lubricant reservoir
system

Cone Design
 All three bit cones have same shape (except that the
first cone has a spear point)
 Basic decision factor: journal or pin angle
 Journal angle (angle between journal axis and
horizontal) specifies outside contour of the bit since all
three cones fit together
 Use of oversize angle increases diameter of cone
(most suitable for soft formation bits)
Dr. Javier Holzmann

Roller Cone Shapes
Third cone Calibration cone
Secondary
cone
Principal
cone

Dr. Javier Holzmann
Cone Design – Journal Angle

Dr. Javier Holzmann
Cone Design
 Important factor affecting the journal angle: degree of
meshing or interfit
 The amount of interfit affects several aspects of bit design:

- Allows more space for tooth depth and bearings as well as
greater cone thickness
- Allows mechanical cleaning of grooves  prevents bit balling
- Provides space for one cone to extend across the hole’s
center to prevent coring effects
- Substitutes cutting action by increasing cone slippage
Dr. Javier Holzmann

Cone Design - Cone Slippage
 Uneven rotation of cones, cones slip while rotating
 Enables rock bit to drill in a scraping action additionally to the
normal grinding or crushing action
- Beneficial in soft formations as gouging and scraping aid to break up
the rock
- Less efficient in harder formations with excessive teeth wear
 May also be achieved by offsetting the cone’s axis

- Often used in soft formation bits
- Hard formation bits have little or no offset to minimize slippage and rely
on grinding and crushing action alone
Dr. Javier Holzmann

Cone Design - Cone Slippage

Dr. Javier Holzmann
Offset
Without offset
With offset
(in hard formation bits)
(in soft formation bits)
Source: Teodoriu, C.: Script Tbt 1, 2014 Source: Heriot-Watt University, Institute of Petroleum Engineering
Dr. Javier Holzmann
Cutting Structure Design
 Selection of teeth of a milled tooth bit and inserts of

an insert bit
 Selection strongly depends on formation type to be

drilled (formation hardness)
 Main considerations:
Height and spacing of teeth or inserts
Dr. Javier Holzmann

Cutting Structure Design – Milled Tooth Bits
 Soft formation bits:

- Deep penetration into rock necessary
 Long, thin & widely spaced teeth (to prevent bit balling)
 Moderately hard formation bits:

- Need to resist heavier loads
- Only scraping/gouging action and limited penetration
 Decreased tooth height & increased tooth width
(spacing has to be sufficient to enable good cleaning)
Note: Bit balling = build up of cuttings on the bit face

Dr. Javier Holzmann
Cutting Structure Design – Milled Tooth Bits
 Hard formation bits:

- Only chipping action and no tooth penetration
- Teeth have to be sufficiently strong to withstand crushing/
chipping action
- Enough teeth necessary to reduce unit load
- Spacing of teeth less critical due to a reduced ROP &
smaller cuttings
 Short and thick teeth
Dr. Javier Holzmann

Cutting Structure Design – Insert Bits
 Soft formation bits:

- Long chisel shaped inserts
- Tungsten carbide hard facing to increase resistivity against
scraping and gouging action
 Hard formation bits:

- Short, wide shaped inserts
- Little or no hard facing on teeth
- Hard facing of outer surface (gauge) of bit
 Otherwise the bit’s outer surface might be eroded by abrasive
formations leading to a decreased hole diameter; or gauge area
might be worn away resulting in possible bit failure
Dr. Javier Holzmann

Typical Insert Types
 Height ≈ 3/4 in. but varies with bit size
Dr. Javier Holzmann
Cutting Structure Design
Dr. Javier Holzmann
Fluid Circulation Design
 Drilling fluid passes through drill string out through
nozzles in the bit
 While passing across the bit face the drilled cuttings
are removed and transported to the annulus
 Initially the mud could only be
ejected from the bit middle which
was less efficient
 Bit balling
 Cone erosion
 Impedes further drilling process
Dr. Javier Holzmann Source: Heriot-Watt University,

Institut für Erdöl- und Erdgastechnik Institute of Petroleum Engineering TBT I_SS 2018 56
Fluid Circulation Design
 Today the mud is generally
ejected through 3 jet nozzles
around the outside of the bit
body to ensure an effective
removal of the drilled cuttings
 Turbulence created by jet
streams is sufficient to clean
the cutters and thereby a
successful further drilling
process is enabled

Dr. Javier Holzmann
Jet Nozzles
 Small rings made out of tungsten carbide
 Available in many standardized sizes (outer diameter)
so that the nozzle is applicable in any bit size
 Nozzle size refers to the ring’s inner diameter and has
to be big enough to stay unplugged from cuttings
 Easily replaceable
 Rings are fitted with an “O” ring seal
 Extended nozzles may be utilized for an enhanced
cleaning process
Dr. Javier Holzmann
Jet Nozzle

Dr. Javier Holzmann
Jet Nozzles
Nozzle wrench for installing

Extended jet nozzle
nozzle and “O” ring
Dr. Javier Holzmann
Jet Nozzle
Jet Nozzle
Dr. Javier Holzmann Photo taken by C.Teodoriu

PDC Bit Design
 Cutting material
 Bit body material
 Cutter rake
 Bit profile
 Cutter density
 Cutter exposure
 Fluid circulation
Dr. Javier Holzmann

Cutting Material
 Cutting surface: PDC - Polycrystalline Diamond

- Synthetic material with 90-95% pure diamond
manufactured into compacts and set into the body of bit
 TSP - Thermally Stable Polycrystralline Diamond bits

- Normal PDC bit cutters were sometimes chipped during
drilling due to internal stresses caused by high
temperatures
 Invention of thermally stable diamond bits
Dr. Javier Holzmann

Bit Body Material
 Cutters of a PDC bit are mounted on a bit body

 Two types of bit bodies:
- Steel body
- Steel shell with Tungsten Carbide matrix surface on body
of the shell
Dr. Javier Holzmann

Bit Body
Matrix-body bit
Steel-body bit
Dr. Javier Holzmann
Bit Body
Matrix-body bit Steel-body bit

Dr. Javier Holzmann
Cutter Rake
 PDC cutters can be set at various rake angles
including back rake and side rake
- Back rake angle determines size of produced cutting for a
given WOB:
- Small rake angle  large cuttings, high ROP but cutter is likely
to break in hard formations
- Larger rake angle  smaller cuttings but increased resistance
to cutter damage
- Assists cleaning by urging cuttings to curl away from bit
- Side rake directs cuttings towards the ank of the bit and
into the annulus
Dr. Javier Holzmann

Bit Profile
 Three basic types of PDC bit crown profiles:
- Flat or shallow cone
- Tapered or double cone
- Parabolic
Dr. Javier Holzmann

Bit Profile
 Flat or shallow
cone profile
- Evenly distributes the WOB among each bit cutter on the

bit
- Disadvantages: limited rotational stability and uneven

wear

Dr. Javier Holzmann
Bit Profile
 Tapered or double
cone profile
- Enables better distribution of the cutters toward bit O.D.,

thereby greater rotational and directional stability and
even wear are achieved

Dr. Javier Holzmann
Bit Profile
 Parabolic profile
- Provides smooth loading over the bit profile and largest

surface contact area thereby even greater rotational and
directional stability and even wear are provided
- Typically used for motor or turbine drilling

Dr. Javier Holzmann
Cutter Density
 Number of cutters per unit area on bit face
 Is increased or decreased to control amount of load

per cutter (has to be balanced against the cutter size)
 High density  cutters must be sufficiently small to

enable effective cleaning of the bit face
Dr. Javier Holzmann

Cutter Exposure
 Amount by which the cutters protrude from the bit body

- Exposure must be high enough to enable effective
cleaning of the bit face
- A too high exposure results in the reduction of the cutter’s
mechanical strength
 High cutter exposure provides more space between bit

body and formation face
 Low exposure provides good backup and therefore
support to the cutters
Dr. Javier Holzmann

Fluid Circulation
 Has to be designed to remove the cuttings effectively
and to cool the bit face
 Can be adapted by raising the fluid’s flowrate and/or

design of the water courses running across the bit face
- But: increased fluid flow may lead to excessive erosion of
the bit face and premature bit failure
 Typically more than three jets used on PDC bits
Dr. Javier Holzmann

PDC Bit Architecture
Jet
Cutters
Nozzles
Bit Diameter
Transport
channels

Dr. Javier Holzmann
Alternative Hydraulic Designs
 Vortex Nozzles
 Clean sweep
 Mudpick
 Switchblade
 Asymmetric
Nozzles

Institut für Erdöl- und Erdgastechnik Courtesy of Schlumberger TBT I_SS 2018 76
Bit Selection
 Many variations concerning drill bit design

 System of comparison charts developed by the IADC
(International Association of Drilling Contractors) for
classifying drill bits in terms of design characteristics
and application:
- System for roller cone bits
- System for fixed cutter bits
- Operational since 1972
- Design and application related coding
Dr. Javier Holzmann

Roller Cone Bit Selection
 Mostly selected by IADC bit comparison charts

 Charts contain bits available from leading bit manufacturers
 Bits classifed according IADC code
 Position of each bit in chart defined by three numbers and
one character:
- 1st Series
- 2nd Type  numeric
- 3rd Bearing & Gage
- 4th Features Available  alphabetic
Dr. Javier Holzmann

IADC Code Roller Cone Bits
1st Number – Series:
 Eight (8) Series or Categories representing particular

formation drillability :
- Series 1 to 3: Milled tooth bits
- Series 4 to 8: Tungsten carbide insert bits
The higher the series number,

the harder/more abrasive the rock
Dr. Javier Holzmann

2nd Number – Type:
 Degree of Hardness
 Each Series subdivided into 3 or 4 Types:
- Type 1: Softest Formation in a Series
Increasing Rock Hardness
- Type 4: Hardest Formation in a Series
Dr. Javier Holzmann

3rd Number – Bearing design and gauge protection

 Seven subcategories
1. Standard roller bearing (non-sealed)
2. Air cooled roller bearings
3. Roller bearing bit with gauge protection (non-sealed)
4. Sealed roller bearings
5. Sealed roller bearings and gauge protection
6. Sealed friction bearings
7. Sealed friction bearings and gauge protection
Dr. Javier Holzmann

4th Character – (optional) features available

 Sixteen (16) Alphabetic Characters
 Most Significant Features:
A - Air Application L - Lug Pads
B - Special Bearing/Seal M - Motor Application
C - Center Jet S - Standard Milled Tooth
D - Deviation Control T - Two-Cone Bit
E - Extended Nozzles W - Enhanced C/S
G - Gage/Body Protection X - Chisel Tooth Insert
H - Horizontal Application Y - Conical Tooth Insert
J - Jet Deflection Z - Other Shape Inserts
Dr. Javier Holzmann

 Examples:
135M or 447X or 637Y or 124E
 135M Soft formation milled tooth bit, roller bearings with

gauge protection and motor application
 447X Soft formation insert bit, friction bearings with gauge

protection and chisel inserts
 637Y Medium-hard insert bit, friction bearing with gauge

protection and conical inserts
 124E Soft formation, milled tooth bit with sealed roller

bearings and extended nozzles
Dr. Javier Holzmann
 Examples:
135M 447X 637Y

Dr. Javier Holzmann
Roller Cone Bit Classification - Summary
 Convenient categorization system

 Design and application code
 Know its limitations
 Use carefully in application decisions
 Consider other sources:
- Offset bit records
- Dull grading
- Performance analysis
Dr. Javier Holzmann

Formation Hardeness - Definition
Hardness UCS (psi) Examples

Ultra Soft < 1,000 gumbo, clay
unconsolidated sands, chalk,

Very Soft 1,000 - 4,000 salt, claystone
Soft 4,000 - 8,000 coal, siltstone, schist, sands
sandstone, slate, shale,

Medium 8,000 - 17,000 limestone, dolomite
quartzite, basalt, gabbro,
Hard 17,000 - 27,000 limestone, dolomite
Very Hard > 27,000 marble, granite, gneiss
UCS = Uniaxial Unconfined Compressive Strength

Dr. Javier Holzmann
Soft Formations
 Consist of shales, clays, and conglomerates

 Hardened steel tooth roller cone bits are optimal

Dr. Javier Holzmann
Medium Formations
 Consist of sandstones, limestones, and dolomites
laced with interbedded shales and clays
 Optimized tungsten carbide insert bits are most

effective

Dr. Javier Holzmann
Hard Formations
 Consist of anhydrides and chert
often laced with interbedded
sands and limestones
 Optimized PDC bits are most

efficient

Dr. Javier Holzmann
Drill Bit Specifications - Bit Weight for Core Bits

Institut für Erdöl- und Erdgastechnik Courtesy Hughes Christensen TBT I_SS 2018 90
How do bits wear out?
 Tooth wear or loss
 Bearings wear
 Gauge wear
 Nozzle wear
Dr. Javier Holzmann

Tooth Wear

Dr. Javier Holzmann
Grading of Dull Bits
 Steel teeth
- Graded in eights of original tooth height that has worn
away
 i.e. T3 means that

3/8 of the original
tooth height is worn
away

Dr. Javier Holzmann
 Tungsten Carbide Insert bit

 i.e. T3 means that 3/8 of the inserts are broken or lost

Dr. Javier Holzmann
 Bearings wear
 i.e. B3 means that 3/8 of the estimated bearing life is gone
Balled up Bit Cracked Cone

Dr. Javier Holzmann
Gauge ring
 Gauge wear
- Bit is either “in-gauge” or “out-of-
gauge”
- Determined by diameter Bit
measurements with a gauge ring
 Examples: - T3 - B3 – I
- T5 – B4 - 0 1/2
Dr. Javier Holzmann

Source: drillingformulas.com
Dr. Javier Holzmann
API Rock Bit Diameter Tolerance Chart
Bit Size Tolerances
inches mm inches mm
3-3/8 to 13-3/4 85.7 to 349.2 + 1/32 - 0 + 0.79 - 0
14 to 17-1/2 355.6 to 444.5 + 1/16 - 0 + 1.59 - 0
> 17-5/8 > 44.7 + 3/32 - 0 + 2.38 - 0

Dr. Javier Holzmann
 How do bits fail?
Washed out Bit Lost Cone
Dr. Javier Holzmann

Grading of Worn PDC Bits
CT - Chipped Cutter BT - Broken Cutter

Less than 1/3 of cutting element is More than 1/3 of cutting element is
gone broken to the substrate
Dr. Javier Holzmann
Grading of Worn PDC Bits
LT - Lost Cutter LN - Lost Nozzle

Bit is missing one or more cutters Bit is missing one or more nozzles
Dr. Javier Holzmann
Grading of Worn Drill Bits
Cracked Zone

Damaged Tri-Cone Bit
 Mode of failure:
- Brittle failures of
Tungsten Carbide
inserts
 Inserts must be
removed before
drilling is (re-)started
or further damage
may occur
Dr. Javier Holzmann

Damaged Tri-Cone Bit
 Mode of failure:
- Wear of the milled
teeth
- Abrasion, erosion &
broken tooth
Dr. Javier Holzmann

How to Improve Bit Performance
 Stabilize the bit

 Maintain minimum mud weight, sand and solids
 Maintain adequate bottom hole cleaning
 Protect the seals - avoid pressure surges
 Thoroughly inspect bit before re-running
 Keep oil from the mud and the seals
 Follow manufacturers recommendations
(i.e. 6,000 lb/in of diameter and 40-60 RPM)
Dr. Javier Holzmann

Improving Roller Cone Bits
Constant Borehole Diameter
Wear resistant zone

Dr. Javier Holzmann
Hard Facing for Gauge Protection
Bit worn but not

undergauged
Hard facing
Source: Heriot-Watt University,

Source: Petroleum Engineering Handbook, Ed. Lake,
Institute of Petroleum Engineering
L. W. and Mitchell, R.F, SPE, USA, 2006
Dr. Javier Holzmann
Improving Roller
Cone Bits
Wear
resistant
zone

How to Improve Bit Life – Optimized BHA Design

Dr. Javier Holzmann
What we have done today
 Drill bit requirements, types & costs

 Roller Cone bit design
 PDC bit design
 Selection & classification of Roller Cone bits
 Bit wear out including examples
 Grading of dull bits
 How to improve bit performance
 Improving bit life
Dr. Javier Holzmann


06.TBT1 Drilling Bits

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06.TBT1 Drilling Bits

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Introduction to Drilling Technology

Dr. Javier Holzmann

Dr. Javier Holzmann

 Drill bit requirements, types & costs

Dr. Javier Holzmann

Dr. Javier Holzmann

 Bit performance is a function of several operating

- Weight on bit (WOB)

Dr. Javier Holzmann

 Low cost per foot drilled

. 1. High drilling rate

3. Drill full-gauge, straight hole

Dr. Javier Holzmann

 Low cost per foot drilled

Dr. Javier Holzmann

Drag Bit Roller Cone Bit Diamond Bit

Diamond bits TC Insert bits Milled Tooth bits

 Diamond bits typically cost several times as much as tri-cone

Dr. Javier Holzmann

 First bits used in rotary drilling

 Decline in use due to:

- If too much WOB was applied excessive torque led to bit

- Tend to drill crooked hole  deviation control necessary

- Limited to drill through uniformly, soft, unconsolidated

Dr. Javier Holzmann

 Most common type of bit world wide

 Cones rotate on bottom of the hole and drill hole

 Classified as milled tooth or insert bits

Dr. Javier Holzmann

Milled tooth bit Insert bit

Dr. Javier Holzmann Source: Heriot-Watt University, Institute of Petroleum Engineering;

Dr. Javier Holzmann Source: Teodoriu, C.: Script Tbt 1, 2014

 The major advances in rock bit design:

Dr. Javier Holzmann

Dr. Javier Holzmann

 Cutting material: diamond

 Today natural diamonds are mostly

 Type of drag bit; no moving cones,

 Cutting action achieved by scraping away the rock

Dr. Javier Holzmann

Dr. Javier Holzmann

Dr. Javier Holzmann

Dr. Javier Holzmann

Source: Heriot-Watt University, Institute of Petroleum Engineering;

Dr. Javier Holzmann Source: Teodoriu, C.: Script Tbt 1, 2014

 TSP = Thermally Stable Polycrystalline (TSP)

 Introduced in the late 1980’s

 Manufactured similarly to PDC bits but can withstand

Dr. Javier Holzmann

PDC bit TCI bit Milled Tooth bit

 Roller Cone Bit Design

 PDC Bit Design

Dr. Javier Holzmann

Dr. Javier Holzmann

Dr. Javier Holzmann

 The cones of a roller cone bit are mounted on journals

Source: Heriot-Watt University, Institute of Petroleum Engineering

 Exploded view of seal and bearing components

 Comparison of journal and roller bearing arrangements