Roller Cone Bit Design

7/24/2019 Roller Cone Bit Design

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Roller cone bit design

Wide varieties of roller cone bits are available. They provide optimum performance in

specific formations and/or particular drilling environments. Modern drill bits incorporate

significantly different cutting structures and use vastly improved materials, resulting in

improved bit efficiency. Manufacturers work closely with drilling companies to collect

information about their bits to identify opportunities for design improvements.

Contents

[hide]

1 Roller cone bit design goals

2 Basic design principles

3 Design methods and tools

o 3.1 How teeth and inserts drill

o 3.2 Bit design method

3.2.1 Bit diameter/available space

3.2.2 Jornal angle

3.2.3 !one o""set

3.2.# $eeth and inserts

# Design as applied to ctting strctre

o

#.1 %nserts/teeth and the ctting strctre

& 'aterials design

o &.1 %nserts and wear(resistant hard("acing materials

&.1.1 )roperties o" tngsten carbide composites

&.1.1.1 $ngsten carbide insert *$!%+ design

&.1.1.2 ,age ctting strctre
http://petrowiki.org/Roller_cone_bit_designhttp://petrowiki.org/Roller_cone_bit_designhttp://petrowiki.org/Roller_cone_bit_design#Roller_cone_bit_design_goalshttp://petrowiki.org/Roller_cone_bit_design#Basic_design_principleshttp://petrowiki.org/Roller_cone_bit_design#Design_methods_and_toolshttp://petrowiki.org/Roller_cone_bit_design#How_teeth_and_inserts_drillhttp://petrowiki.org/Roller_cone_bit_design#Bit_design_methodhttp://petrowiki.org/Roller_cone_bit_design#Bit_diameter.2Favailable_spacehttp://petrowiki.org/Roller_cone_bit_design#Journal_anglehttp://petrowiki.org/Roller_cone_bit_design#Cone_offsethttp://petrowiki.org/Roller_cone_bit_design#Teeth_and_insertshttp://petrowiki.org/Roller_cone_bit_design#Design_as_applied_to_cutting_structurehttp://petrowiki.org/Roller_cone_bit_design#Inserts.2Fteeth_and_the_cutting_structurehttp://petrowiki.org/Roller_cone_bit_design#Materials_designhttp://petrowiki.org/Roller_cone_bit_design#Inserts_and_wear-resistant_hard-facing_materialshttp://petrowiki.org/Roller_cone_bit_design#Properties_of_tungsten_carbide_compositeshttp://petrowiki.org/Roller_cone_bit_design#Tungsten_carbide_insert_.28TCI.29_designhttp://petrowiki.org/Roller_cone_bit_design#Gauge_cutting_structurehttp://petrowiki.org/Roller_cone_bit_design#Roller_cone_bit_design_goalshttp://petrowiki.org/Roller_cone_bit_design#Basic_design_principleshttp://petrowiki.org/Roller_cone_bit_design#Design_methods_and_toolshttp://petrowiki.org/Roller_cone_bit_design#How_teeth_and_inserts_drillhttp://petrowiki.org/Roller_cone_bit_design#Bit_design_methodhttp://petrowiki.org/Roller_cone_bit_design#Bit_diameter.2Favailable_spacehttp://petrowiki.org/Roller_cone_bit_design#Journal_anglehttp://petrowiki.org/Roller_cone_bit_design#Cone_offsethttp://petrowiki.org/Roller_cone_bit_design#Teeth_and_insertshttp://petrowiki.org/Roller_cone_bit_design#Design_as_applied_to_cutting_structurehttp://petrowiki.org/Roller_cone_bit_design#Inserts.2Fteeth_and_the_cutting_structurehttp://petrowiki.org/Roller_cone_bit_design#Materials_designhttp://petrowiki.org/Roller_cone_bit_design#Inserts_and_wear-resistant_hard-facing_materialshttp://petrowiki.org/Roller_cone_bit_design#Properties_of_tungsten_carbide_compositeshttp://petrowiki.org/Roller_cone_bit_design#Tungsten_carbide_insert_.28TCI.29_designhttp://petrowiki.org/Roller_cone_bit_design#Gauge_cutting_structurehttp://petrowiki.org/Roller_cone_bit_design


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&.1.1.3 Diamond(enhanced tngsten carbide inserts *$!%s+

&.1.1.# $ngsten carbide hard "acing

- pecial prpose roller cone bit designs

o -.1 'onocone bits

o -.2 $wo(cone bits

Re"erences

0 ee also

oteworth papers in 4ne)etro

15 67ternal lin8s

Roller cone bit design goals

Roller-cone bit design goals epect the bit to do the following!

"unction at a low cost per foot drilled.

#ave a long downhole life that minimi$es re%uirements for tripping.

&rovide stable and vibration-free operation at the intended rotational speed and

weight on bit 'W()*.

+ut gauge accurately throughout the life of the bit.

To achieve these goals, bit designers consider several factors. mong these are!

The formation and drilling environment.

pected rotary speed.

pected weight on bit 'W()*.

#ydraulic arrangements.

nticipated wear rates from abrasion and impact.
http://petrowiki.org/Roller_cone_bit_design#Diamond-enhanced_tungsten_carbide_inserts_.28TCIs.29http://petrowiki.org/Roller_cone_bit_design#Tungsten_carbide_hard_facinghttp://petrowiki.org/Roller_cone_bit_design#Special_purpose_roller_cone_bit_designshttp://petrowiki.org/Roller_cone_bit_design#Monocone_bitshttp://petrowiki.org/Roller_cone_bit_design#Two-cone_bitshttp://petrowiki.org/Roller_cone_bit_design#Referenceshttp://petrowiki.org/Roller_cone_bit_design#See_alsohttp://petrowiki.org/Roller_cone_bit_design#Noteworthy_papers_in_OnePetrohttp://petrowiki.org/Roller_cone_bit_design#External_linkshttp://petrowiki.org/Roller_cone_bit_design#Diamond-enhanced_tungsten_carbide_inserts_.28TCIs.29http://petrowiki.org/Roller_cone_bit_design#Tungsten_carbide_hard_facinghttp://petrowiki.org/Roller_cone_bit_design#Special_purpose_roller_cone_bit_designshttp://petrowiki.org/Roller_cone_bit_design#Monocone_bitshttp://petrowiki.org/Roller_cone_bit_design#Two-cone_bitshttp://petrowiki.org/Roller_cone_bit_design#Referenceshttp://petrowiki.org/Roller_cone_bit_design#See_alsohttp://petrowiki.org/Roller_cone_bit_design#Noteworthy_papers_in_OnePetrohttp://petrowiki.org/Roller_cone_bit_design#External_links


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esign focal points include!

The bit body

+one configurations

+utting structures

Metallurgical, tribological, and hydraulic considerations in engineering bit design

solutions. 'Tribology is a science that deals with the design, friction, wear, and lubrication

of interacting surfaces in relative motion.*

)asic design principles

rill-bit performance is influenced by the environment in which it operates. The way that bits

are designed and their operating performance takes into consideration many operating

choices, such as!

pplied W()

Rotary speed

#ydraulic arrangements

lso of critical importance in bit performance and design are environmental factors, such as!

The nature of the formation to be drilled

#ole depth and direction

+haracteristics of drilling fluids

The way in which a drill rig is operated

ngineers consider these factors for all designs, and every design should begin with close

cooperation between the designer and the drilling company to ensure that all applicable

inputs contribute to the design.

esign activities are focused principally on four general areas!

Material selection for the bit body and cones

eometry and type of cutting structure to be used
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Mechanical operating re%uirements

#ydraulic re%uirements

The dimensions of a bit at the gauge 'outside diameter* and pin 'arrangement for

attachment to a drillstem* are fied, usually by industry standards, and resultant design

dimensions always accommodate them 'Fig 1*.

Fig. 1Roller-cone bit general nomenclature.

"or roller-cone bits, steels must have!

ppropriate yield strength

#ardenability

0mpact resistance

Machineability

#eat treatment properties

The ability to accept hard facing without damage

+utting structure designs provide efficient penetration of the formation's* to be drilled and

accurately cut gauge. The importance of bearing reliability in roller-cone bits cannot be

understated. 0n an operational sense, bearings, seals, and lubrication arrangements function


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as a unit, and their designs are closely interrelated. )earing systems must function normally

when!

1nder high loads from W()

0n conditions of large impact loads

While immersed in abrasive- and chemical-laden drilling fluids

0n relatively high-temperature environments.

#ydraulic configurations are designed to efficiently remove cuttings from cutting structure

and bottomhole and then evacuate cuttings to the surface.

esign methods and tools

How teeth and inserts drill

To understand design parameters for roller-cone bits, it is important to understand how roller-

cone bits drill. Two types of drilling action take place at the bit. crushing action takes place

when weight applied to the bit forces inserts 'or teeth* into the formation being drilled 'W()

inFig. 2*. 0n addition, a skidding, gouging type of action results partly because the designed

ais of cone rotation is slightly angled to the ais of bit rotation 'rotation in Fig. 2*. 2kidding

and gouging also take place because the rotary motion of a bit does not permit a penetrated

insert to rotate out of a crushed $one it has created without causing it to eert a lateral force

at the $one perimiter. )oth effects contribute to cutting action 'Fig. 2*.

Fig. 2Cutting actions for roller-cone bits.

Bit design method

The bit geometry and cutting structure engineering method of )entson has since 3456 been

the root from which most roller-cone bit design methods have been designed 738. lthough

modern engineering techni%ues and tools have advanced dramatically from those used in

3456, )entson9s method is the heritage of modern design and continues to be useful for

background eplanation.
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Bit diameter/available sace

Well diameter and the bit diameter re%uired to achieve it influence every design feature

incorporated into every efficient bit. The first consideration in the physical design of a roller-

cone bit is the permissible bit diameter or, in the words of the designer, available space.

very element of a roller-cone bit must fit within a circle representative of the re%uired well

diameter. The &0 has issued specifications establishing permissible tolerances for standard

bit diameters.: The si$es of ;ournals, bearings, cones, and hydraulic and lubrication features

are collectively governed by the circular cross section of the well. 0ndividually, the si$ing of

the various elements can, to an etent, be varied. Repositioning or altering the si$e or shape

of a single component nearly always re%uires subse%uent additional changes in one or more

of the other components. 0n smaller bits, finding good compromises can be difficult because

of a shortage of space.

!ournal angle

describes an angle formed by a line perpendicular to the ais of a bit and the

ais of the bit9s leg ;ournal. =ournal angle is usually the first element in a roller-cone bit

design. 0t optimi$es bit insert 'or tooth* penetration into the formation being drilled? generally,

bits with relatively small ;ournal angles are best suited for drilling in softer formations, and

those with larger angles perform best in harder formations.

Cone offset

To increase the skidding-gouging action, bit designers generate additional working force by

offsetting the centerlines of the cones so that they do not intersect at a common point on the

bit. This is defined as the hori$ontal distance between the ais of a bit and the

vertical plane through the ais of its ;ournal. (ffset forces a cone to turn within the limits of

the hole rather than on its own ais. (ffset is established by moving the centerline of a cone

away from the centerline of the bit in such a way that a vertical plane through the cone

centerline is brllel to the vertical centerline of the bit. )asic cone geometry is directly affected

by increases or decreases in either ;ournal or offset angles, and a change in one of the two

re%uires a compensating change in the other. 2kidding-gouging improves penetration in soft

and medium formations at the epense of increased insert or tooth wear. 0n abrasive

formations, offset can reduce cutting structure service life to an impractical level. )it

designers thus limit the use of offset so that results ;ust meet re%uirements for formation

penetration.

"eeth and inserts

Tooth and insert design is governed primarily by structural re%uirements for the insert or

tooth and formation re%uirements, such as!


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&enetration

0mpact

brasion

With borehole diameter and knowledge of formation re%uirements, the designer selects

structurally satisfactory cutting elements 'steel teeth or Tungsten +arbide 0nserts 'T+0s** that

provide an optimum insert/tooth pattern for efficient drilling of the formation.

"actors that must be considered to design an efficient insert/tooth and establish an

advantageous bottomhole pattern include!

)earing assembly arrangement

+one offset angle

=ournal angle

+one profile angles

0nsert/tooth material

0nsert/tooth count

0nsert/tooth spacing

When these re%uirements have been satisfied, remaining space is allocated between

insert/tooth contour and cutting structure geometry to best suit the formation.

0n general, the physical appearance of cutting structures designed for soft, medium, and

hard formations can readily be recogni$ed by the length and geometric arrangement of their

cutting elements.

esign as applied to cutting structure

pplication of design factors produces diverse results 'Fig. #*. The cutting structure on the

left is designed for the softest formation types? that on the right, for formations that are

harder.


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Fig. #Cutting structure for soft $left% and hard $right% formations.

The action of bit cones on a formation is of prime importance in achieving a desirable

penetration rate. 2oft-formation bits re%uire a gouging-scraping action. #ard-formation bits

re%uire a chipping-crushing action. These actions are governed primarily by the degree to

which the cones roll and skid. Maimum gouging-scraping 'soft-formation* actions re%uire a

significant amount of skid. +onversely, a chipping-crushing 'hard-formation* action re%uires

that cone roll approach a condition with very little skidding. "or soft formations, a

combination of small ;ournal angle, large offset angle, and significant variation in cone profile

is re%uired to develop the cone action that skids more than it rolls. #ard formations re%uire a

combination of large ;ournal angle, no offset, and minimum variation in cone profile. These

will result in cone action closely approaching true roll with little skidding.

&nserts/teeth and the cutting structure

)ecause formations are not homogeneous, si$able variations eist in their drillability and

have a large impact on cutting structure geometry. "or a given W(), wide spacing between

inserts or teeth results in improved penetration and relatively higher lateral loading on the

inserts or teeth. +losely spacing inserts or teeth reduces loading at the epense of reduced

penetration. The design of inserts and teeth themselves depends largely on the hardness

and drillability of the formation. &enetration of inserts and teeth, cuttings production rate, and

hydraulic re%uirements are interrelated, as shown in "able 1.

"able 1-&nterrelationshi Between &nserts' "eeth' H(draulic Re)uirements' *nd "he Formation

"ormation and cuttings removal influence cutting structure design. 2oft, low-compressive-

strength formations re%uire long, sharp, and widely spaced inserts/teeth. &enetration rate in

this type of formation is partially a function of insert/tooth length, and maimum insert/tooth

depth must be used. @imits for maimum insert/tooth length are dictated by minimum

re%uirements for cone-shell thickness and bearing-structure si$e. 0nsert/tooth spacing must

be sufficiently large to ensure efficient fluid flows for cleaning and cuttings evacuation.


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Re%uirements for hard, high-compressive-strength formation bits are usually the direct

opposite of those for soft-formation types. 0nserts are shallow, heavy, and closely spaced.

)ecause of the abrasiveness of most hard formations and the chipping action associated

with drilling of hard formations, the teeth must be closely spaced 'Fig. +*. This close spacing

distributes loading widely to minimi$e insert/tooth wear rates and to limit lateral loading on

individual teeth. t the same time, inserts are stubby and milled tooth angles are large to

withstand the heavy W() loadings re%uired to overcome the formation9s compressive

strength. +lose spacing often limits the si$e of inserts/teeth.

Fig. +Comarison of softer &*,C +2( $left% and harder # $right% cutting structures

0n softer and, to some etent, medium-hardness formations, formation characteristics are

such that provisions for efficient cleaning re%uire careful attention from designers. 0f cutting

structure geometry does not promote cuttings removal, bit penetration will be impeded and

force the rate of penetration 'R(&* to decrease. +onversely, successful cutting structure

engineering encourages both cone shell cleaning and cuttings removal.

Materials design

Materials properties are a crucial aspect of roller-cone bit performance. +omponents must

be resistant to abrasive wear, erosion, and impact loading. The eventual performance and

longevity results for a bit take into account several metallurgical characteristics, such as!

#eat treatment properties

Weldability

The capacity to accept hard facing without damage

Machineability

&hysical properties for bit components are contingent on the raw material from which a

component is constructed, the way the material has been processed, and the type of heat

treatment that has been applied. 2teels used in roller-cone bit components are all melted to

eacting chemistries, cleanliness, and interior properties. ll are wrought because of grain

structure refinements obtained by the rolling process. Most manufacturers begin with forged


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blanks for both cones and legs, because of further refinement and orientation of

microstructure that result from the forging process.

2tructural re%uirements and the need for abrasion and erosion resistance are different for

roller-cone bit legs and cones. &redictably, the materials from which these components areconstructed are normally matched to the special needs of the component. "urthermore,

different sections of a component often re%uire different physical properties. @eg ;ournal

sections, for eample, re%uire high hardenabilities that resist wear from bearing loads,

whereas the upper portion of legs are configured to provide high tensile strengths that can

support large structural loads.

Roller-cone bit legs and cones are manufactured from low-alloy steels. @egs are made of a

material that is easily machinable before heat treatment, is weldable, has high tensile

strength, and can be hardened to a relatively high degree. +ones are made from materialsthat can be easily machined when soft, are weldable when soft, and can be case hardened

to provide higher resistance to abrasion and erosion.

&nserts and wear-resistant hard-facing materials

Tungsten carbide is one of the hardest materials known. 0ts hardness makes it etremely

useful as a cutting and abrasion-resisting material for roller-cone bits. The compressive

strength of tungsten carbide is much greater than its tensile strength. 0t is thus a material

whose usefulness is fully gained only when a design maimi$es compressive loading while

minimi$ing shear and tension. Tungsten carbide is the most popular material for drill-bit

cutting elements. #ard-facing materials containing tungsten carbide grains are the standard

for protection against abrasive wear on bit surfaces.

When most people say they do not refer to the chemical compound 'W+*

but rather to a sintered composite of tungsten carbide grains embedded in, and

metallurgically bonded to, a ductile matri or binder phase. 2uch materials are included in a

family of materials called ceramic metal, or )inders support tungsten carbide

grains and provide tensile strength. )ecause of binders, cutters can be formed into useful

shapes that orient tungsten carbide grains so they will be loaded under compression.

Tungsten carbide cermets can also be polished to very smooth finishes that reduce sliding

friction. Through the controlled grain si$e and binder content, hardness and strength

properties of tungsten carbide cermets are tailored for specific cutting or abrasion

resistances.

The most common binder metals used with tungsten carbide are iron, nickel, and cobalt.

These materials are related on the periodic table of elements and have an affinity for

tungsten carbide 'cobalt has the greatest affinity*. Tungsten carbide cermets normally have

binder contents in the 6A to 36A 'by weight* range. )ecause tungsten carbide grains are


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metallurgically bonded with binder, there is no porosity at boundaries between the binder

and grains of tungsten carbide, and the cermets are less susceptible to damage by shear

and shock.

0roerties of tungsten carbide comosites

The process of cermet properties makes it possible to eactly match a material

to the re%uirements for a given drilling application. +omposite material hardness, toughness,

and strength are affected by!

Tungsten carbide particle si$e 'normally : to 6 Bm*

&article shape

&article distribution

)inder content 'as a weight percent*

s a generali$ation, increasing binder content for a given tungsten carbide grain si$e will

cause hardness to decrease and fracture toughness to increase. +onversely, increasing

tungsten carbide grain si$e affects both hardness and toughness. 2maller tungsten carbide

particle si$e and less binder content produce higher hardness, higher compressive strength,

and better wear resistance. 0n general, cermet grades are developed in a range in which

hardness and toughness vary oppositely with changes in either particle si$e or binder

content. 0n any case, subtle variations in tungsten carbide content, si$e distribution, and

porosity can markedly affect material performance 'Fig. *.

Fig. Hardness' toughness' and wear resistance of cemented tungsten carbide.

"ungsten carbide insert $"C&% design

T+0 design takes the properties of tungsten carbide materials and the geometric efficiency

for drilling of a particular rock formation into account. s noted, softer materials re%uire

geometries that are long and sharp to encourage rapid penetration. 0mpact loads are low,

but abrasive wear can be high. #ard formations are drilled more by a crushing and grinding

action than by penetration. 0mpact loads and abrasion can be very high. Tough materials,

such as carbonates, are drilled by a gouging action and can sustain high impact loads and


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high operating temperatures. Cariations in the way that drilling is accomplished and rock

formation properties govern the shape and grade of the correct T+0s to be selected.

The shape and grade of T+0s are influenced by their respective location on a cone. 0nner

rows of inserts function differently from outer rows. 0nner rows have relatively lower rotationalvelocities about both the cone and bit aes. s a result, they have a natural tendency to

gouge and scrape rather than roll. 0nner insert rows generally use softer, tougher insert

grades that best withstand crushing, gouging, and scraping actions. auge inserts are

commonly constructed of harder, more wear-resistant tungsten carbide grades that best

withstand severe abrasive wear. 0t is thus seen that re%uirements at different bit locations

dictate different insert solutions. large variety of insert geometries, si$es, and grades

through which bit performance can be optimi$ed are available to the designer 'Fig. * 7:8.

Fig. "(ical insert t(es $height 34 in. but varies with bit si5e%.

6auge cutting structure

The most critical cutting structure feature is the gauge row. auge cutting structures must

cut both the hole bottom and its outside diameter. )ecause of the severity of gauge

demands on a bit, both milled tooth and insert type bits can use either tungsten carbide or

diamond-enhanced inserts on the gauge. 1nder abrasive conditions, severe wear or gauge

rounding is common, and, at high rotary speeds, the gauge row can eperience

temperatures that lead to heat checking, chipping, and breakage.

,iamond-enhanced tungsten carbide inserts $"C&s%

iamond-enhanced inserts are used to prevent wear in the highly loaded, highly abradedgauge area of bits and in all insert positions for difficult drilling conditions. They are made up

of polycrystalline diamond compact '&+*, which is chemically bonded, synthetic diamond

grit supported in a matri of tungsten carbide cermet. &+ has higher compressive strength

and higher hardness than tungsten carbide. 0n addition, diamond materials are largely

unaffected by chemical interactions and are less sensitive to heat than tungsten carbides.

These properties make it possible for diamond-enhanced materials to function normally in

drilling environments in which tungsten carbide grades deliver disappointing or

unsatisfactory results '"able 2* 7D8,7E8,758
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"able 2-Comarison 7f ,iamond' 0,C' *nd "ungsten Carbide 8aterials

When diamond-enhanced inserts are designed, higher diamond densities increase impact

resistance and ability to economically penetrate abrasive formations. 0ncreased diamond

density increases insert cost, however. 0n the past, diamond-enhanced inserts have been

available only in symmetrical shapes. The first of these was the semiround top insert. Today,

some manufacturers have developed processes that make it possible to produce comple

diamond-enhanced insert shapes.

"ungsten carbide hard facing

#ard-facing materials are designed to provide wear resistance 'abrasion, erosion, and

impact* for the bit 'Fig. *. To be effective, hard facing must be resistant to loss of material

by flaking, chipping, and bond failure with the bit. #ard facing provides wear protection on

the lower 'shirttail* area of all roller-cone bit legs and as a cutting structure material on

milled-tooth bits 'Fig. *.

Fig. "(ical hard-facing alications on a milled-tooth bit.

Fig. 9:loded view of seal and bearing comonents.

#ard facing is commonly installed manually by welding. hollow steel tube containing

appropriately si$ed grains of tungsten carbide is held in a flame until it melts. The resulting


14/17

molten steel bonds, through surface melting, with the bit feature being hard faced. 0n the

process, tungsten carbide grains flow as a solid, with molten steel from the rod, onto the bit.

The steel then solidifies around the tungsten carbide particles, firmly attaching them to the

bit.

2pecial purpose roller cone bit designs

8onocone bits

Monocone bits were first used in the 34DFs. The design has several theoretical advantages

but has not been widely used. )it researchers, encouraged by advances in cutting structure

materials, continue to keep this concept in mind, because it has the room for etremely large

bearings and has very low cone rotation velocities, which suggest a potential for long bit life.

While of a certain general interest, monocone bits are potentially particularly advantageousfor use in small-diameter bits in which bearing si$ing presents significant engineering

problems.

Monocone bits drill differently from three-cone bits. rilling properties can be similar to both

the beneficial crushing properties of roller-cone bits and the shearing action of &+ bits.

+utting structure research thus focuses partly on eploitation of both mechanisms

encouraged by the promise of efficient shoe drillouts and drilling in formations with hard

stingers interrupting otherwise formations. Modern ultrahard cutter materials properties

can almost certainly etend insert life and epand the range of applications in which thisdesign could be profitable. The design also provides ample space for no$$le placements for

efficient bottomhole and cutting structure cleaning.

"wo-cone bits

The origin of two-cone bit designs lies in the distant past of rotary drilling. The first roller-

cone patent, issued in ugust 34F4, covered a two-cone bit. s with monocone bits, two-

cone bits have available space for larger bearings and rotate at lower speeds than three-

cone bits. )earing life and seal life for a particular bit diameter are greater than for

comparable three-cone bits. Two-cone bits, although not common, are available and perform

well in special applications 'Fig ;*. Their advantages cause this design to persist, and

designers have never completely lost interest in them.


15/17

Fig. ;"wo-cone bit.

The cutting action of two-cone bits is similar to that of three-cone bits, but fewer inserts

simultaneously contact the hole bottom. &enetration per insert is enhanced, providing

particularly beneficial results in applications in which capabilities to place W() are limited.

The additional space available in two-cone designs has several advantages. 0t is possible to

have large cone offset angles that produce increased scraping action at the gauge. 2pace

also enables ecellent hydraulic characteristics through room for placement of no$$les very

close to bottom. 0t also allows the use of large inserts that can etend bit life and efficiency.

Two-cone bits have a tendency to bounce and vibrate. This characteristic is a concern for

directional drilling. )ecause of this concern and advances in three-cone bearing life and

cutting structures, two-cone bits do not currently have many clear advantages. s with many

roller-cone bit designs, however, modern materials and engineering capabilities may resolve

problems and again underscore their recogni$ed advantages.

References

3. G)entson, #.., and 2mith 0ntl. 0nc. 3456. Roller-+one )it esign. @os ngeles,

+alifornia! &0 ivision of &roduction, &acific +oast istrict.

:. G&ortwood, ., )oktor, )., Munger, R. et al. :FF3. evelopment of 0mproved

&erformance Roller +one )its for Middle astern +arbonate rilling pplications.

&resented at the 2&/0+ Middle ast rilling Technology +onference, )ahrain,

::-:E (ctober. 2&-H::4I-M2. http!//d.doi.org/3F.:33I/H::4I-M2 .

D. GJeshavan, M.J., 2iracki, M.., and Russell, M.. 344D. iamond-nhanced 0nsert!

Kew +ompositions and 2hapes for rilling 2oft-to-#ard "ormations. &resented at

the 2&/0+ rilling +onference, msterdam, Ketherlands, ::-:5 "ebruary. 2&-

:5HDH-M2.http!//d.doi.org/3F.:33I/:5HDH-M2 .

E. G2alesky, W.=. and &ayne, ).R. 34IH. &reliminary "ield Test Results of iamond-

nhanced 0nserts for Three-+one Rock )its. &resented at the 2&/0+ rilling

+onference, Kew (rleans, @ouisiana, 35-3I March. 2&-36335-

M2.http!//d.doi.org/3F.:33I/36335-M2.

5. G2alesky, W.=., 2winson, =.R., and Watson, .(. 34II. (ffshore Tests of iamond-

nhanced Rock )its. &resented at the 2& nnual Technical +onference and

hibition, #ouston, Teas, :-5 (ctober. 2&-3IFD4-

M2. http!//d.doi.org/3F.:33I/3IFD4-M2 .
http://petrowiki.org/Roller_cone_bit_design#cite_ref-r1_0-0http://petrowiki.org/Roller_cone_bit_design#cite_ref-r2_1-0http://dx.doi.org/10.2118/72298-MShttp://petrowiki.org/Roller_cone_bit_design#cite_ref-r3_2-0http://dx.doi.org/10.2118/25737-MShttp://petrowiki.org/Roller_cone_bit_design#cite_ref-r4_3-0http://dx.doi.org/10.2118/16115-MShttp://petrowiki.org/Roller_cone_bit_design#cite_ref-r5_4-0http://dx.doi.org/10.2118/18039-MShttp://petrowiki.org/Roller_cone_bit_design#cite_ref-r1_0-0http://petrowiki.org/Roller_cone_bit_design#cite_ref-r2_1-0http://dx.doi.org/10.2118/72298-MShttp://petrowiki.org/Roller_cone_bit_design#cite_ref-r3_2-0http://dx.doi.org/10.2118/25737-MShttp://petrowiki.org/Roller_cone_bit_design#cite_ref-r4_3-0http://dx.doi.org/10.2118/16115-MShttp://petrowiki.org/Roller_cone_bit_design#cite_ref-r5_4-0http://dx.doi.org/10.2118/18039-MS


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Roller cone bit classification

!0ntroduction to Roller-+one and &olycrystalline iamond rill )its

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