overview of rock bits

Beijing Petroleum University

Introduction of oil well drilling bits

Roller cone bit

Diamond bit

Roller Cone Bits for Oil Well Drilling


I. Tri-cone rock bit

II. Single–cone bit

III.Application instructions


Tri-cone Rock Bits

Introduction to bit type

Main bit structure

Special structure

Additional structure

Diameter Code Series Code Classification

Code

Additional

Structure Feature

Code


ROCK BIT TYPE

Bit Series Code：


INTRODUCTION TO ROCK BIT TYPE

For tri-cone rock bits, series codes are divided into 9 standard

series according to the main structure features of bearing and

sealing. Major improvement in bit structure is regarded as

special structure, and standard series with the special structure

or special structure combinations formed into special series.

While the series code of the single cone bit is indicated by “Y

x ”. “Y” means one cone, and “x” is the design sequence letter,

which means different design features. The series code of oil

well drilling bits are shown in the Table.

Bit Series Code： Item

No.

Main Structure Features of

Bearing and Sealing

Standard

Series

Special Series

T

(special gage

protection

D

（equally

worn teeth）

B

（dual water course

with low nozzle

recess）

1 Rubber O ring sealed journal

bearing

H HT HD HB

2 Rubber O ring sealed journal

bearing(improved type)

HA HAT HAD HAB

3 Metal face sealed journal bearing HJ HJT HJD HJB

4 Floating sealed journal bearing HF HFT HFD HFB

5 Rubber O ring sealed floating

bearing(improved type)

FA FAT FAD FAB

6 Rubber O ring sealed roller bearing GA GAT GAD GAB

7 Metal face sealed roller bearing GJ GJT GJD GJB

8 Floating sealed roller bearing GF GFT GFD GFB

9 Non-sealed roller bearing W

10 Single cone bit with rubber O ring

sealed journal bearing

YA



Bit Classification Code：

Formation Structure feature

normal air cool Roller sealed sealed sealed sealed

Lithology roller roller Bearing roller roller journal journal

bearing bearing &gaging bearing &gaging bearing gaging

Classificaion

Series

Grading 1 2 3 4 5 6 7

soft with low 1 111 114 115 116 117

1 Compressive 2 121 126 127

Strength and 3 131 134 135 136 137

High drillability 4

Medium 1 211 214 217

2 Hardness with 2 221

High compressive 3

Strength 4

Hard formation 1 316

3 With

semiabrasive

2 321

And abrasive 3

Steel teeth

bit

4 346 347

Very soft with low 1 415 417

4 Compressive 2 427

Strength and 3 435 437

High drillability 4 445 447

Soft to medium 1 512 515 517

5 With low 2 527

Compressive 3 532 535 537

Strength 4 545 547

Medium hardness 1 612 615 617

6 With high 2 627

Compressive 3 632 637

Strength 4

hard formation 1 712 715

7 With 2

Semiabrasive 3 732 737

And abrasive 4

Very hardness 1

8 Formation 2

Insert b

it

With 3 832 837

The classification code of bit

consists of three digits in

accordance with the requirements

in SPE/IADC 23937. The first

digit stands for the cutting

structure and the formation series

code; the second one stands for

the formation classification code;

and the last one is the structure

feature code of the bit. See the

table.


INTRODUCTION TO

ROCK BIT TYPE

Additional Structure Features Code：



When bits need to be improved or to be

reinforced to meet the special requirement

of drilling application and the formation,

the additional structure features, which

indicated by one or more letters, will be

added to the classification code. See the

table.

Additional Structure Features Code：

Code additional structure feature

Ｃ center nozzle

Ｅ extended nozzle recess

Ｇ reinforced bit head

Ｌ bit head OD stablizer lug

Ｙ conical tungsten carbide insert

H diamond gage teeth



For Example：

8 1/2 HJT 537 GL

Reinforced bit head OD and Bit head OD stabilization pad

Insert bit for drilling in soft to medium hard formation with low compressive strength

Metal face sealed journal bearing,special gage protection

Bit diameter is 215.9mm



Main Bit Structures

Structures of


INTRODUCTION TO TRI-CONE BIT

H series

HA series

HJ series

GA series

GJ series

W series

K series

HF series

FA series

H series Bit Structure



H series bit is O ring sealed journal bearing bit ,which

can stand comparative high bit weight under the normal

rotary speed.The main features are as follows: 1).Taking

good advantage of the cutting ability and cutting speed

by optimizing the design of compact numbers and rows,

the exposure height and the special shaped compacts.

2).Being able to stand high WOB by using ring locked

cone bearing. 3).Improving the seizure resistance of the

bearing by applying copper inlays in the ID of cone.

4).Increasing the reliability of bearing seal by using the

high saturated Buna-N rubber O ring seal with optimized

compression draught, and etc.

HA series Bit Structure



HA series bit is an improved type of H series product. Some improvement has been made in the bearing, cutting structure and sealing area besides the advantage of H series bit. The loading capacity and seizure resistance of the bearing is 1.5 times higher than that of H series bit, the penetration rate is also increased correspondingly. The main features are as follows: 1). O ring seal made of the more wear resistance high saturated Buna-N with the increased seal section, and adding sealing flange at the outer end of the sealing area increase the reliability of the seal. 2). The hard facing on the surface of head bearing, the copper inlays and the silver plating applied in the ID of cone improve the loading capacity and seizure resistance. 3). The bit bearing can be ball locked or ring locked. Bit with ring lock bearing can stand high weight on bit and bit with ball lock bearing can be applied to high rotary speed drilling.

Bit Leg

head Bearing

Cone Bearing

Flange For Sealing

O Ring Seal

HJ series Bit structure



HJ series bit is the metal face sealed journal bearing bit. Using metal face seal(MFS)-one of the most advanced sealing technology in the world, this series of bit can perform consistently in high speed drilling application, and is the ideal tool for drilling directional well and horizontal well. The main features are as follows: 1).A pair of well designed high precision metal rings are used to form the bearing axial dynamic sealing, which make the friction force on the sealing surfaces reduced by 70% to 80%.Two elastic rubber energizers are separately located in the head and cone sealing areas to form static seal,and the sealing compression is optimized to ensure good contact always being kept on the sealing surface of the two metal rings. With the reducing of the friction heat and friction force, HJ series bits have excellent features that applicable for high RPM. 2).The dynamic sealing rings of the metal face sealing system are metal seals, and the static seals are made of high saturated Buna-N that more heat resistant than conventional Buna-N. Therefore, HJ series bits feature with excellent heat resistance.3)Taking advantage of ball locked cone, which is applicable for high speed drilling.

GA SERIES Bit Structure



GA series bit is the rubber O ring sealed roller bearing bit, which is the economical and ideal tool for high RPM drilling application. The main features are as follows:

1). The roller sealed bearing structure, with the roller in the groove recessed into the cone, increases the size of journal, which can bear high WOB and suit for high RPM drilling.

2).Thrust bearing couple surfaces are treated with anti-friction and hardening processes, which increase both the loading capacity and the seizure resistance.

GJ series Bit Structure



GJ series bit is the metal face sealed roller

bearing bit. This series of bit can perform

consistently in high speed drilling

application, and is the ideal tool for drilling

directional well and horizontal well.

2222 W SERIES Bit Structure



W series bit is non-sealed roller bearing bit, which is the economical and ideal tool for high RPM drilling and geothermal drilling application. The main features are as follows:

1).W series bit has the following types of bearing structures: roller-ball-roller-thrust(for bit larger than 12-1/4"). This series of bit can be operated in high RPM drilling.

2).With the non-sealed bearing, the drilling fluid can go directly into the bearing cavity to cool the bearing, which is applicable for geothermal drilling.

K SERIES Bit Structure

It is non-sealed roller

air bearing bit. It is

only used for mining.



e

浮动密封钻头



HF series Bit Structure

HF series bit is floating sealed journal bearing bit that were developed on the basis of HA series products by using floating sealing technology. The main features are as follows: 1). Compared with HA series bit, the HF series bit features that a set of metal retaining ring and O ring seal are used to form the floating seal combination, the O ring seal forms end face sealing and radial sealing with the bearing sealing surfaces of cone and head. The floating seal combination can move with the cone, resulting in the off-center floating sealing, which eliminating the negative effect of the radial play of bearing on the O ring seal during working,and extending the service life of seals. 2).Compared with the conventional O ring seal, the compression of the floating seal rubber ring is decreased by 50%, which reduces the friction heat, and makes the HF series bit applicable for high RPM. The drilling fluid is directed to the floating sealing cavity through the well designed watercourse to cool the O ring. The floating seal combination features with the excellent heat resistance.



O ring sealed and floating sealed comparison diagram

Bit Structure FA series

Comparison diagram of floating bearing and journal bearing



FA series bit is a kind of newly developed high speed O ring sealed floating journal bearing rock bit. It is the ideal tool for drilling in directional well and horizontal well. The main features are as follows:

1).Taking advantage of floating bearing structure technology by adding the floating sleeve between the surfaces of journal bearing and adding floating button between the thrust faces. This decreases the relative linear velocity of the bearings and reduces the temperature of the friction surfaces, which increasing the PV value and make the bearing applicable for high speed drilling.

2). The floating parts of the bearing are made of new material which featured with high strength, high resilience, high heat resistance, and high abrasive resistance, and the surface is treated with solid lubrication grease.

3). Using ball locking bearing makes the bit more applicable for high RPM.

Bit Structure



FA series

Roller Floating Bearing Bit Structure

Three- dimension diagram



Roller Floating Bearing Bit Structure



special Structures



i. Extra Gage Protection (T)

ii.Equally Worn Compacts Structure(D)

Extra Gage Protection (T) Special Structure



Trimmer Structure feature：

1.Adding one row of trimmers between the gage row

and the heel row teeth. The trimmers will break the

uncut rock ribs on the wall of borehole, and minimize

wearing on the gage teeth and cone shell.

2.For extra gage protection steel bit, the shape of teeth

and the build-up welding material are improved

besides adding gage trimmers. Inverted radius tooth

geometry is used on all rows of teeth, which increases

the depth of the build-up welding material on teeth.

The composite material with crack resistance, impact

resistance and better abrasion resistance has been

applied in the gauge welding.

Equally Worn Compacts Structure(D)

Equally Worn Compacts

Special Structure

Structure feature：

Unequal width crest compacts and

unequal width offset “super scoop”

chisel-shape compacts are inserted in

each land of the cone. With the types of

compacts characterized by equally

worn, high strength and high breakage

rate, the bit life can be effectively

extended and the penetration rate can

be increased about 10%.



Additional Structures



i. Center Nozzle (C)

ii.Extended Nozzle (E)

iii.Reinforced Bit Head OD (G)

iv.Bit Head OD Stabilization Pad(L)

v. Conical Compacts(tungsten carbide

insert) (Y)

vi.Diamond Enhanced Gage Compacts (H)

Center Nozzle

Center nozzle

Additional Structure

Structure Feature：



Center nozzle is used

in the center of the

bit to enhance the

cleaning action on

the compacts and

prevent the bit from

balling up. The

center nozzle is

normally used in 7-

7/8" and larger bit

for drilling in soft

formation.

Extended Nozzle

Extende

d nozzle





Using the extended nozzle decreases the distance from the nozzle orifice to the bottom hole,and increases the hydraulic horsepower. The created high speed jet flow enhanced the cross flow, which can improve the earth breaking rate and thoroughly flush the bottom hole.

Reinforced Bit Head OD

Reinfor

ced bit

head OD



The wear resistance and reliability of

the bit head OD can directly affect the

bit life in drilling applications, so, hard

facing applied on bit head OD is very

important, especially in high abrasive

formation, deep drilling and motor

drilling applications. This is achieved by

pressing the special carbide inserts or

hard facing applied on the bit head OD

and shirttail.



Bit Head OD Stabilization Pad(L)

Bit head stabilization pad



In order to improve the wear

resistance of the bit head OD in the

kick off sections of horizontal,

cluster and directional well drilling

applications, the stabilization pad is

used on the bit head OD to overcome

the off center wear caused by the

load deflection and gravity





Conical Compacts (Y)


In hard plastic formation drilling applications, e.g.

when the compact crest is too wide, it is very difficult

to penetrate the formation, the penetration rate of the

conventional insert bit during drilling in hard plastic

formation is very low. The upper section of the conical

compacts is a long conical shape with chiseling and

crushing actions, which can get twice the result with

the half of the effort.




Diamond Enhanced gage compacts (H)


The gage protection is significantly reinforced and the

bit life is prolonged by inserting the diamond enhanced

gage compacts in the heel row and gage row of the

cone.


Single Cone Rock Bit(YA)


INTRODUCTION TO SINGLE CONE BIT

The main structure features:

The series of single cone bit is developed on the basis of the mature manufacturing technology of tri-cone rock bit and diamond bit, which is applicable for slim hole drilling. The main features are as follows:

1. Using two stage gage protection of the cone and the bit body, with active cutting gage protection compacts and passive anti-friction gage protection compacts inserted on the bit body.



The main structure

features:

2. Staggered compacts

arrangement on the cone, and

optimized the cone shape, the

numbers of the row, the

numbers of compacts, and

the compacts exposure height.






3. Two watercourses structure of

main and auxiliary are used for the

hydraulic system with a jet nozzle

and a divergent nozzle, and

optimized the nozzle combinations.





4. The advanced Buna-N rubber seals are

used for the journal and bearing pin sealing,

and optimized the sealing compression and

the special protective structure designing,

which ensured the reliability of the bearing

sealing.

5. Hard facing layer applied on head bearing

and copper inlay applied on the surface of

cone ID improve the performance of bearing.

6. Ball lock bearing makes the bit applicable

for high RPM.

rock bit nozzle

S—

standard

P—

protection

M—Mini

extended

INTRODUCTION TO ROCK BIT NOZZLES


Application Instructions


Operation instructions Cautions for applications of rock bits The impact of rotary speed on ROP The impact of WOB on ROP The influence of WOB X RPM on the life of the bearing The influence of WOB X RPM on the life of bit teeth Reasonably determine the proper time for pulling up


Operation Instructions:

(1) Inspect the appearance and measure the OD of the bit before it is tripped in, ensuring

the teeth have no breakage, the weld seam without crack and porosity. Those bits, which

have such defects, cannot be tripped in.

(2) Select the suitable nozzle in accordance with the hydraulics program, and make sure

that the nozzles are in good condition.

(3) To mount the nozzle, should use the special tools---retaining ring pincers. Protect the

“o”ring from any damage.

(4) When make up the bit, proper breakout plate should be used to avoid any damage to the

nozzle and bit body.

(5) Tripping in of the bit should be operated stably, especially for the tungsten carbide bit

and the speed of tripping in must be appropriately controlled. Care should be taken when

bit is run into the hard formations; high angle well and irregular well bore to avoid the bit

colliding with the borehole wall. For such collision may cause the tungsten carbide break

or damage to the shirttail, therefore it will lead to the premature failure of the sealing ring.



Operation Instructions:

(6) When the new bit trips in with 3～5 meters from the bottom, mud should be

thoroughly circulated. When the bit is about 1 meter from the bottom, the bit should

be rotated to reach the bottom hole. Once the bit contacts with the bottom hole, it

should rotate slowly with low WOB for a while, because the bottom hole pattern may

differ from the profile of the new bit, and some teeth of the new bit touch the bottom

earlier than the others, thus the stress concentrate on these teeth and probably break

them. While the bit is making the bottom hole pattern, its bearing is running in, then

the sealing will be in good condition. Running-in process under low WOB and slow

rotary speed should be at least 30 minutes.

(7) Start up the rotary table under any WOB is prohibited.

(8) The rotary speed must be controlled in the recommended ranges, because if the

bit rotates with too high linear velocity, it may cause the bearing over-heated or

snapped-in, and the premature failure to the “o” ring seal.



Cautions for Applications of Rock Bits

(1) The tungsten carbide bit must be used in the wells with clean bottom-hole and

without any fish.

(2) If the well bore is under-gauge or under abnormal condition, which requires

long time reaming, the tungsten carbide bit cannot be used. Because the heel row

compacts of the bit will expose to the high counteracting force from the borehole

wall, thus the cone gage or shirttail will be severely worn, leading to the undersize

of the bit, the failure of the seal, the premature damage to the bearing, or even such

serious accidents as breaking or loss of the cone.

(3) In order to prevent any underground problem, and give a full play to the

capability of the bit and save the consequent economic cost, the tungsten carbide bit

should not be lowered into the well under following circumstances, as the surface

equipment can not work properly, the instrument malfunction, the mud property not

in accordance with demands or the purifying system can not achieve the predicted

effect.



The Impact of Rotary Speed on ROP

(1) In shallow and soft formation, generally, the bit undergoes

shearing action to break the formation. The rate of penetration is

direct proportional to the rotary speed. The cutters are worn only

a little if the bit is run in high rotary speed.

(2) In medium hard formations, the bit undergoes shearing 、

percussion and crushing action. The ROP can not increase so

soundly following the increase of the RPM as it is in the soft

formations. So in the practical drilling operation, the moderate

RPM and medium to high WOB are advised to increase ROP.

(3) In deep and hard formations, the bit undergoes percussion

and crushing action to break formation. The cutters should

contact with the rock much longer than it is needed to break the

rock, then the breaking efficiency can be increased. So in these

formations , the increase of the RPM can not result in the

soundly increase of the ROP.



Soft formation

Medium formation

Hard formation

Rate o

f pen

etration

Rotary speed

The impact of WOB on ROP The practical drilling operation prove that the WOB has

linear relationship with the ROP, as the following Figure

shows : in the starting-up period, the WOB is low and there is

only a little cuttings , the RPM is direct proportional to the

square of WOB. If the WOB is increased gradually, the

cleaning condition becomes worse, the WOB is in the linear

relationship with the ROP. Later on, if the WOB is

continually increased , the ROP will only increase slowly and

even drop some amount.

In soft formations, when the WOB has already reached to

some values, the ROP then do not increase obviously, and

even there are some decrease occurred. It is due to the

unclean condition in the bottom-hole.

In hard formations, it is needed to adopt relatively high

WOB to break formation due to the high compressive

strength. So in this hard formations , high WOB should be

applied.



RO

P

WOB

A

P1

B

P2

The influence of WOB X RPM on the life of the bearing

The life of the sealed journal bearing is related to the linear velocity of

the bearing. The high linear velocity will bring about the high friction

force and result in the rapid increase of temperature on the bearing. Thus

snap-in and damage may occur. In order to optimize the performance of

the journal bearing bit, we adopt the concept of “WN capability factor”

for the drilling operation technician. The value of WN is determined by

the structure of each journal bearing, it is the multiplication of WOB and

RPM.

C=W·N

Where W---WOB(KN) N---RPM(R/MIN) C---Bearing Capability Factor(KN‧R/MIN)



The influence of WOB and RPM on the life of bit teeth

The breakage and fracture of teeth are mainly caused by the

fatigue and overstress, no matter what brings such damage, the

main reason is caused by “percussion". The strength of

percussion is related to the hardness of the rock, WOB on per

unit area and the linear velocity of the cone. The percussion

load is direct proportional to the applied WOB. So the WOB

and RPM directly or indirectly influence on the life of teeth .

Bit manufacturers always have recommended WOB and RPM

in tables for their bits. The upper limits for the WOB and RPM

recommended in the table can not be used at the same time.



Reasonably determine the proper time for pulling-up Generally, according to the service life and dullness of last bit , and taking the information

of the offset well , together with the features of the new bit and formation lithology of the

present well as reference , we can estimate preliminary the service life of the new bit. And

also by taking the following factors into consideration, we can determine when to pull it out.

(1) Judging the wear of the bearing: If the bearing is worn, the movement of the bearing

will be stuck. The torque of the bit will increase suddenly or fluctuate continually, which

can be judged from the load on the rotary table and the diesel engine. In deep section or

small size bit, the torque should be read from the torque meter. When the solids enter the

bearing, the journal bearing will be damaged more quickly than the rolling bearing. So in

the practical operation, the changes of the torque should be closely observed and analyzed

to prevent the loss of the cone.

(2) Judging the dullness of teeth: If there are no noticeable lithology changes, when the

teeth is worn, the footage will not match with the increase of drilling hour, the ROP will

decrease gradually. Therefore, we can adopt the method of analyzing every meter cost,

calculate the changes of every meter cost according to the drilling hours and footages. If the

other drilling parameters are the same, when some conspicuous increase of cost are noticed,

the bit should be pulled and changed.




The end !

overview of rock bits

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