Dril bit technology presentation

Dril bit technology presentation

Network of Excellence in Training

Drill Bit Technology

Drill Bit Technology

• Lecture Contents;,

– Lecture Objectives, – Drill Bit Types, – Bit Design,

– Bit Selection, – Bit Evaluation,

• Lecture Objectives;

– By the end of this lecture YOU should be able to:

• Recognize different bit types,

• Describe various process of bit design with respect to roller cone bits and PDC bits,

• Select bits for various formation types and drilling conditions,

• Grade bits using the IADC Dull Grading System,

• Utilize the IADC code to describe and compare bits,

• Identify important operational aspects that effect bit

performance,

Drill Bit Technology

• Drag Bits (Fish Tail):

Drill Bit Types

• Roller Cone Bits: Milled tooth bits,

Drill Bit Types

• Roller Cone Bits: Inserts bits,

Drill Bit Types

• Natural Diamond Bits:

Drill Bit Types

• PDC Bits:

Drill Bit Types

• TSP Bits:

Drill Bit Types

• Roller Cone Bits;

• A bearing is a device that sits between the cone and its

attachment to the leg of the bit to reduce the force of friction

as the cone rotates

• Roller cone bit bearings must operate under severe

conditions temperature and loads,

• Roller cone bits use three types of bearing in the bearing

• Roller Cone Bits;

bearings near the end, or nose,of the cone.

This bit also uses ball bearings,as well as another set of smaller roller

bearings near the end, or nose,of the cone

• Roller Cone Bits;

– Bearing Assembly:

• Journal Bearing Bits:

Bit Design

• Roller Cone Bits;

– Bearing Assembly:

• Sealed Bearing Bit Lubrication:

Bit Design

• Roller Cone Bits;

Bit Design

• All the three cones have the same shape with the No 1 cone

having a spear point,

• The basic factor to be decided is the journal or pin angle,

• The journal angle is formed between the axis of the journal

and the horizontal,

• One important factor which affect the journal angle is the

degree of meshing or interfit, (the distance that the crests of

• Roller Cone Bits;

• Roller Cone Bits;

– Cone Design:

Bit Design

• Roller Cone Bits;

• Milled Tooth Bits;

Bit Design

– Cutting Structure:

• Soft Formation bits:

– These types require deep penetration into the rock so the teeth are long, thin and widely spaced (to prevent balling),

– The long teeth take-up space, so the bearing size must be reduced This is allowable since the loading should nit be excessive in soft formation.

• Milled Tooth Bits;

– Cutting Structure :

Bit Design

• Medium Formation Bits:

decrease and their width increased,

penetration,

cleaning.

• Milled Tooth Bits;

– Cutting Structure :

Bit Design

• Hard Formation Bits:

– These do not rely on tooth penetration so the teeth are shorter than those used for softer formations

– the teeth must be strong enough to withstand the crushing/chipping action and sufficient numbers of teeth should

be used to reduce the unit load, – Spacing of teeth is lees critical since the ROP is reduced and the cuttings tend to be smaller.

• Roller Cone Bits;

– Cutting Structure : Comparison;

Bit Design

Soft = = = = = = = = = = ==> Hard

• Insert Bits;

– Cutting Structure :

Bit Design

milled tooth bits,

wear This allows an insert bit to be used over a wider range of formation types than is usually impossible for a milled tooth bit.

• Insert Bits;

– Cutting Structure :

Bit Design

• Roller Cone Bits;

Bit Design

Cutter Hardfacing

• Roller Cone Bits; :

Bit Design

Gauge Protection

• Roller Cone Bits;

– Fluid Circulation:

Bit Design

Jet Nozzle

• Roller Cone Bits;

– Fluid Circulation:

Bit Design

• The second stage is to mix the artificial diamond crystals

with catalyst/binder in a temperature exceeding 1400oC and pressure of 750,000 psi

Bit Design

• PDC Bits;

– Cutter Material:

Bit Design

• PDC Bits;

Bit Design

– Profile:

• PDC Bits;

Bit Design

– Cutter Density:

• This is a compromise between reducing the amount of load per

cutter by increasing the number of cutters and yet keeping the number of cutters small enough to allow efficient cleaning of the face of the bit,

– Cutter Exposure:

• This is important to ensure good cleaning of the bit face,

• Full exposure provides more space between the bit body and the

formation,

• Partial exposure provide good back-up therefore support the

• PDC Bits;

Bit Design

– Fluid Circulation:

• Circulation across the bit face must be designed to remove

the cuttings efficiently and also cool the bit face,

• These requirements may be satisfied by increasing the fluid flowrate,

• The increased fluid flowrate may however cause excessive

erosion of the face and premature bit failure

• Roller Cone Bits;

– In order to select the best bit for a particular application,

comparison charts are often used,

– These charts contain bit availability from the major

suppliers,

– The position of each bit in the chart is defined by three

numbers and one character,

– The sequence of numeric characters defines the following:

• Series,

• Types,

• Bearing Features.

Bit Selection

• Roller Cone Bits;

Bit Selection

– Series:

• Series 1-3 apply to milled tooth bits and classified as soft, medium or hard,

• Series 4-8 apply to insert bits and are classified as soft,

medium, hard and extra hard

• Each series is divided into 4 types according to the hardness

application of the bit,

• Roller Cone Bits;

Bit Selection

– Bearing Features:

There are slight variation in the categories depending on the comparison chart used for example:

“1” Means a standard roller bearing,

“2” Means air cooled roller bearing,

“3” Means a roller bearing bit with gauge protection,

“4” Means sealed roller bearings are included,

“5” Means both sealed roller bearings and gauge protection included,

“6” Means sealed friction bearing included,

“7” Means both sealed friction bearings and gauge protection included.

Bit Selection – Comparison Chart

• Roller Cone Bits;

Bit Selection

• This character is used to define additional features of the bit

for example:

formation milled tooth bit with sealed roller and extended nozzles.

• The term soft , medium and hard are very broad

categorization of the geological strata

• Roller Cone Bits ;

diameter) and high RPM (125-250),

• Medium Formations:

• Roller Cone Bits;

• Why Evaluation?

– As each bit is pulled out from the hole, its physical

appearance is inspected and graded according to the wear it has sustained,

– The evaluation is useful for the following reasons:

• Improve bit type selection,

• Identify the affect of drilling parameters,

• Gain experience on bit life and when to pull before failure,

Bit Evaluation

• Why Evaluation?

Bit Evaluation

• IADC Dull Grading System:

– Column 1- Inner Cutting Structure (I):

• Report the condition of the cutting structure on the inner

2/3rds of the bit for roller cone bits and inner 2/3rds radius

of a fixed cutter bit,– Column 2 - Outer cutting Structure (O):

• This report the condition of the cutting structure on the outer

1/3rd of the bit for roller cone and outer 1/3rd radius of a fixed cutter bit

Bit Evaluation

• IADC Dull Grading System:

– Column 1/2 – Inner/Outer cutting Structure:

Bit Evaluation

• In column 1 and 2 a liner scale from 0 to 8 is used to describe

the condition of the cutting structure as follows:

– Steel Tooth Bits: a measure of the lost tooth height,

» 0 - indicates no lost in tooth height,

» 8 - indicates total loss of tooth height.

– Insert Bits: a measure of total cutting structure reduction due to lost, worn and/or broken inserts:

» 0 - indicates no lost in tooth height,

• IADC Dull Grading System:

– Column 1/2 – Inner/Outer cutting Structure:

Bit Evaluation

» 0 - indicates no loss of cutter or diamond height,

» 8 - indicates total loss of cutter or diamond height.

– Column 3- Cutting Structure Dull characteristics (D):

• Report the major dull characteristic of the bit cutting

• IADC Dull Grading System:

Bit Evaluation

– Column 4 - Cutting Structure Location (L):

• Report the location of the face of the bit where the major

cutting structure dulling characteristics occur,

• This may be reported in the form of letter or number code,– Column 5 - Bearing Condition (B):

• Report the condition of roller cone bits,

• The grading will depend on the type of bit,

• This space will always be occupied by an X for fixed cutter.

• IADC Dull Grading System:

Bit Evaluation

– Column 6 - Gauge (G):

• Report on the gauge of the bit,

• The letter “I” is used if the bit has no gauge reduction,

• If the bit has gauge reduction it is reported in 1/16 of an inch.– Column 7 - Remarks (O):

• Report any dulling characteristics of the bit in addition to that

• IADC Dull Grading System:

Bit Evaluation

– Column 8 - Reason for pulling (R):

• Report the reason for pulling out of the hole.

– Generally:

• Part of the bit description in the daily drilling report as Tooth

Bearing & Gauge (T B G),

• For half used rock bit, the description will be [4,4, O 1/16”],

• For fixed cutter and core bits, the description will denote the

percentage recovered (e.g Rec 80%)

• Bit performance is judged on:

– How much footage it drilled, – How fast it drilled (ROP), – How much it cost to run ( the capital cost of the bit plus the

operating costs of running it in the hole) per foot of hole drilled.

• The best method of assessing bit performance is by the cost:

Bit Performance

C = Overall cost $/ft,

C = Bit cost ($),

C T

R

• Roller Cone Bit:

– Penetration rate is function of many parameters including:

• Roller Cone Bits;

• Roller Cone Bits;

1714

Q

HHPb = Pb Q = Flowrate (gpm),

P b = Pressure drop across the bit (psi),

• Roller Cone Bits;

• Roller Cone Bits;

an increased torque with no ROP increase.

– Hole Deviation: In some areas WOB will produce bending in

the drillstring leading to crooked hole The drillstring should be properly stabilized to prevent this happening

– Bearing Life: the greater the load on the bearings, the shorter

their operational hours WOB must be balanced against bearing life.

• Roller Cone Bits;

• Roller Cone Bits;

Bit Performance

• The rotary speed will depend on time taken for an individual

tooth to exceed the threshold, penetrate and remove the cuttings The RPM applied to the bit will be function of:

– Type of Bit: In general, lower RPMs are used for insert bits

than for milled tooth bits This is to allow the inserts more time

to penetrate the formation The insert crushes a wedge of rock and then forms a crack which loosens the fragment of rock

– Type of Formations: Harder formations are less easily

penetrated and so require low RPM A high RPM may cause damage to the bit or the drillstring.

• Roller Cone Bits;

– Rotary Speed:

Bit Performance

ROP Hard Formation

Soft Formation

• Roller Cone Bits;

Bit Performance

– Mud Properties:

• In order to prevent an influx of formation fluids into the

wellbore, mud hydrostatic pressure should be slightly higher (safety margin),

• The overbalance forces the liquid part of the mud into the formation and deposit the solids part as filter cake,

• In porous formation this will lead to a thick plaster being

formed which prevents any further entry of fluids to the formations,

• this also happens at the bottom of the hole where plaster

• Roller Cone Bits;

– Mud Properties:

Bit Performance

rock is exceeded, cracks develop which loosen small fragments or chips from the formation,

pressure being exerted below the chip,

chip against the formation,

• Roller Cone Bits;

– Mud Properties:

Bit Performance

• To reduce the hold down effect:

kick),

removal is essential to increase drilling efficiency.

• Roller Cone Bits;

– Mud Properties:

Bit Performance

Chip

Pore Pressure

Tooth

HP

• Roller Cone Bits;

– Mud Properties:

Bit Performance

• Dynamic chip hold down effect is not significant since the

filter cake is much thinner,

• The hold down may occur when cracks form around the

chip, mud enters the cracks to equalize the pressure,

• In doing so pressure drop is created which tends to hold the

chip against the bottom of the hole,

• In general both static and dynamic hold down effects cause

bit balling and hence reduce the ROP

• Roller Cone Bits;

– Mud Properties:

Bit Performance

Tooth Chip

• PDC Bits:

• The basic trend is that PDC bits drill faster with low WOB

and high RPM,

• They also require higher RPM than roller cone bits,

• The general recommendation is that the highest RPM that

can be achieved should be used

• PDC bits drill with more torque and RPM than roller cone bits And the WOB should be sufficient enough to avoid premature failure

• Generally, When RPM is increased WOB should be reduced.

Bit Performance

• Now YOU should be able to:

– Identify different bit types, – Describe various process of bit design with respect to

roller cone bits and PDC bits,

conditions,

– Utilize the IADC code to describe and compare bits,

Drill Bit Technology

Network of Excellence in Training

Drill Bit Technology

End of Lecture