Drill Bit Types Advantages and Disadvantages

• Presented By Jyoti Anischit• Tribhuvan University• Msc in Engineering Geology

DRILLING EQUIPMENTS

DRILLS

PERCUSSION DRILLS

ABRASION DRILLS

FUSION PIERCING

DRILL BITS

DETACHABLE BITS

FORGED BITS

Selecting Ideal Bit

• Drilling Cost per foot• Drillability• Abrasiveness• Type of Reservoir• Cost of the Bit• Depth

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)

Common Types of Drilling Bits

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.

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

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

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.

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.

Types of Bits1. 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.

Drag Bits

• Design Features

– Number & shape of cutting blades/stones

– Size and location of the water courses

– Metallurgy of the bit and cutting elements

Drag Bits– Drilling is achieved by physically blowing cuttings from

the bottom of the bore-hole

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

Fishtail Drag Bit

Drag Bits

• Cutter may be made from:– Steel– Tungsten carbide– Natural diamonds– Polycrystalline diamonds

(PDC)

Drag Bits

• Types of Drag Bits

– Steel cutter bits (Fishtail Type)

– Diamond bits

– Polycrystalline diamond bits

• Best for

– Soft formations

– Uniform formations

– unconsolidated formations

• Now, replaced by other types in all area

Steel Cutter Bits

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

– 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

• Shape of crown profit:

– Step type

– Long taper (straight hole, high wt.)

– Short taper (easier to clean)

– Non taper (directional drilling)

Diamond Bits

• 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

• 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

Top View of Diamond Bit

Side View of Diamond Bit

Natural Diamond Bits PDC Bits

Natural Diamond

bit

junk slotcuttings

radial flow

high Dp across face

Soft Formation

Diamond bit

Larger diamonds Fewer diamonds Pointed nose

Hard Formation

Diamond bit

Smaller diamonds More diamonds Flatter nose

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

PDC bits

Courtesy Smith Bits

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)

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

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

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.

Grading of Worn PDC Bits

CT - Chipped CutterLess than 1/3 of cutting element is gone

BT - Broken CutterMore than 1/3 of cutting element is broken to the substrate

Grading of Worn PDC Bits – cont’d

LT - Lost CutterBit is missing one or more cutters

LN - Lost NozzleBit is missing one or more nozzles

Table 7.7 - Commonly Used Bit Sizes For Running API Casing

Casing Size Coupling Size Common Bit (OD in.) (OD in.) Sizes Used (in.) 4 1/2 5.0 6, 6 1/8, 6 1/4

5 5.563 6 1/2, 6 3/4

5 1/2 6.050 7 7/8, 8 3/8

6 6.625 7 7/8, 8 3/8, 8 1/2

6 5/8 7.390 8 1/2, 8 5/8, 8 3/4

7 7.656 8 5/8, 8 3/4, 9 1/2

7 5/8 8.500 9 7/8, 10 5/8, 118 5/8 9.625 11, 12 1/4

9 5/8 10.625 12 1/4, 14 3/4

10 3/4 11.750 1513 3/8 14.375 17 1/2

16 17 2020 21 24, 26

Rolling Cutter bits

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

Tungsten Carbide Insert Bit

Milled ToothBit

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)

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

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)

Example tungsten carbide insert cutter used in rolling cutter Bits

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

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

Fluid flow through water courses in bit

Proper bottomhole

cleaning is very important

Fluid flow through jets in the bit (nozzles)

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

Milled Tooth Bit

(Steel Tooth)

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

Tungsten Carbide

Insert Bits

Roller Cone Bearings

Bearings

• Ball Bearings (point contact)

• Roller Bearings (line contact)

• Journal bearing (area contact)

• Lubrication by drilling fluid . . . or . . .

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

Grading of Dull Bits How do bits wear out?

• Tooth wear or loss • Worn bearings

• Gauge wear

Grading of Dull BitsHow 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

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

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

Grading of Dull Bits How do bits fail?

Washed out Bit Lost Cone

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

Thank you for ur kind attention

• Email me at Jyotikhatiwadaanischit@gmail.comJyoti AnischitTU EGEO, 2nd semesterRoll no. 12