Rolling Cutter Bits

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1

PETE 411Well Drilling

Lesson 8

Rolling Cutter Bits



2

Notice

Some seniors have not submitted their

"Student Internship Report". PETE 300.

Look for the list.

The requirement is on the web. See

department homepage



3

Lesson 8 - Bits cont’d

Rolling Cutter Bits

• Steel Tooth (milled tooth)

• Carbide Tooth (tungsten carbide insert)

Grading of Worn Bits

Bit Performance

Buoyancy



4

Read:

Applied Drilling Engineering, Ch.5

(bits)

HW #4:

ADE 1.18. 1.19, 1.24Due Monday, Sept. 23, 2002



5

Tungsten

Carbide Insert

Bit

Milled

Tooth

Bit



6



7

Rotary Drill Bits

Rol ler Cutter B its - rock b i ts

First rock bit introduced in 1909 by

Howard Hughes

• 2 - cone bit

• Not self-cleaning



8

Rotary Drill Bits

• Improvements • 3 - cone bit (straighter hole)

• Intermeshing teeth (better cleaning)

• Hard-facing on teeth and body

• Change from water courses to jets

• Tungsten carbide inserts

• Sealed bearings

• Journal bearings



9

Rotary Drill 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



10Fluid flow through water courses in bit

Proper

bottomhole

cleaning is veryimportant



11Fluid flow through jets in the bit (nozzles)



12

Rotary Drill Bits

Mil led Too th B it (Steel Too th )

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 hardfacing

on one side

High drilling rates - especially in softer

rocks



13

Mil led

Too th B i t(Steel

Tooth)



14

Rotary Bits

Tungsten Carbide Insert B i ts

• 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 is a very hard, brittle material)



15

Tungsten

Carbide

InsertBi ts



16

Sealed Bearing

Lubrication System



17

Sealed, self-lubricated roller bit

journal bearing

design details

INSERTS

SILVER PLATED BUSHING

RADIAL SEAL

BALL BEARING

GREASE RESERVOIR CAP

BALL RETAINING

PLUG

BALL RACE



18

RollerCone

Bear ings



19

Bearings

Ball Bearings (point contact)

Roller Bearings (line contact)

Journal bearing (area contact)

Lubrication by drilling fluid . . . or . . .



20

Bearings

Journal Bear ings (area contact)

• Wear-resistant hard surface on journal

• Solid lubricant inside cone journal race

• O - ring seal

• Grease

• Sealed Bearings (s ince 1959) • Grease lubricant (much longer life)

• Pressure surges can cause seal to leak!

Compensate?



21

Grading of Dull Bits

How do bits wear out?

Tooth wear or loss

Worn bearings

Gauge wear



22

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 wornaway



23


Broken or Lost Teeth

• Tungs ten Carb ide Insert b it

e.g. T3 means that 3/8 of the inserts

are broken or lost



24


How do bits fail?

• Bearings: B3 means that an estimated

3/8 of the bearing life is gone

Balled up BitCracked Cone



25


How do bits fail?

Washed out Bit Lost Cone



26


How do bits wear out?

Examples:

• T3 – B3 - I

• T5 – B4 - 0 1/2

Gauge Wear:

• Bit is either in-Gauge or out-of-Gauge

• Measure wear on diameter (in inches),using a gauge ring

BIT

GAUGE RING



27

IADC ROLLER CONE

BIT CLASSIFICATION

SYSTEM



28

IADC System

Operational since 1972

Provides a Method of Categorizing Roller

Cone Rock Bits

Design and Application related coding

Most Recent Revision

„The IADC Roller Bit Classification System‟

1992, IADC/SPE Drilling Conference

Paper # 23937



29

IADC Classification

4-Character Design/Application Code

First 3 Characters are NUMERIC

4th Character is ALPHABETIC

135M or 447X or 637Y



31

Sequence

Numeric Characters are defined:

Series 1st

Type 2 nd

Bearing & Gage 3rd

Alphabetic Character defined: Features Available 4th

135M or 447X or 637Y





33

Define Hardness

Hardness UCS (psi) Examples

Ultra Soft < 1,000 gumbo, clay

Very Soft 1,000 - 4,000

unconsolidated sands, chalk,

salt, claystone

Soft 4,000 - 8,000 coal, siltstone, schist, sands

Medium 8,000 - 17,000sandstone, slate, shale,

limestone, dolomite

Hard 17,000 - 27,000 quartzite, basalt, gabbro,limestone, dolomite

Very Hard > 27,000 marble, granite, gneiss

UCS = Uniaxial Unconfined Compressive Strength



34

Type

SECOND CHARACTER

Degree of Hardness

Each Series divided into 3 or 4 „Types‟

Type 1 Softest Formation in a Series

Type 4 Hardest Formation in a Series

Increasing Rock Hardness

135M or 447X or 637Y



35

Bearing & Gage

THIRD CHARACTER

Bearing Design and Gage Protection

Seven (7) Categories1. Non-Sealed (Open) Roller Bearing

2. Roller Bearing Air Cooled

3. Non-Sealed (Open) Roller Bearing Gage Protected

4. Sealed Roller Bearing5. Sealed Roller Bearing Gage Protected

6. Sealed Friction Bearing

7. Sealed Friction Bearing Gage Protected

135M or 447X or 637 Y



36

Features Available

FOURTH CHARACTER

Features Available (Optional)

Sixteen (16) Alphabetic Characters

Most Significant Feature Listed(i.e. only one alphabetic character should be selected).

135M or 447X or 637 Y



37

IADC Features Available

A - Air Application B - Special Bearing/Seal

C - Center Jet

D - Deviation Control

E - Extended Nozzles

G - Gage/Body Protection

H - Horizontal Application

J - Jet Deflection

L - Lug Pads M - Motor Application

S - Standard Milled

Tooth

T - Two-Cone Bit W - Enhanced C/S

X - Chisel Tooth Insert

Y - Conical Tooth Insert

Z - Other Shape Inserts

135M or 447X or 637 Y



38

Categorization - 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.



39



40

A “D” in front signifies

a diamond bit

D1 - D5 signifies a

natural diamond or

PDC bit

D7 - D9 signifies a

natural diamond or

PDC core bit



41

How to Improve Bit Performance

1. Stabilize the bit2. Maintain minimum mud weight, sand and

solids

3. Maintain adequate bottom hole cleaning4. Protect the seals - avoid pressure surges

5. Thoroughly inspect bit before re-running

6. Keep oil from the mud, and from the seals

7. Follow manufacturers recommendations

(e.g. 6,000 lb/in of diameter and 40-60 RPM)



42



43

Buoyancy

Archimedes‟ Principle:

“The upthrust (buoyancy force)experienced by a submerged body is equal

to the weight of fluid displaced.”



44How would you prove this? What is “buoyancy”?

Buoyancy Force (B)



45

Buoyancy Force (B)

B = Wt. Of fluid displaced

(i)

Solid

(ii)

Hollow

(iii)

Hollow but closed atBottom

LD4

V 2

1

B1 = Vol.*Density

f

2

1 LD4

B

f

2

1

2

22 L)DD(4

B

LD4

V 2

23

f 22

3 LD4

B

L D DV )(4

2

1

2

22

Note: L=Length of submerged section



46

Buoyancy Force

Example: Case 1 (Solid Cylinder)

D = 7 in

L = 12,000 ft

= 14.5 #/gal

Calculate Buoyancy Force



47

Buoyancy Force

Solution: B1 = Weight of fluid displaced

= Volume of cyl * density of mud

=

LD4

2

gal

lb

in

gal

f t

in

f t in B

5.14

23112*000,1274 3

22

1

B1= 347,860 lbf



48

Alternate Solution

Hydrostatic pressure at bottom:

PB= 0.052 * 14.5 * 12,000 = 9,048 psig

Cross-sectional area = 222 in486.38)7(

4D

4

221 in*in

lb486.38*048,9area*pressureforceB

B1 = 348,210 lbf B1= 347,860 lbf (?)







Buoyancy force

= Volume of mud displaced

* mud density

= Weight of fluid displaced

Alternatively:

Buoyancy Force

2511223344PA-PA-PA-PAPAB

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Rolling Cutter Bits