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8/10/2019 Pages From Drilling Engineering

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Although core bits sometimes drill faster than normal bits in the same formation

since less rock is to be destroy, the additional tripping time to retrieve the cores

makes core drilling a costly operation.

Side Wall Coring

As alternative to drilling for a core, side wall coring provides rock samples that are

smaller than common cores but in general large enough to allow geologists or

reservoir engineers to evaluate the particular formation parameters.

5.2 rill !it Classi"cation

rill bits are classi"ed by #AC $#nternational Association of rilling Contractor% to

identify similar bit types made from di&erent manufacturers.

5.2.' (oller !it Classi"cation

)he bit classi"cation in use up to '*+2 applied three digits, the new one applies four.

)he "rst three digits of the old classi"cation remained basically unchanged $although

come modi"cations and etensions were proposed in the mean time%, the additional

fourth letter provides in general information about the bit characteristics.

-irst digit

' soft formations with low compressivestrength and high drillability

2 medium to medium hard formationswith high compressive strength/ard semi0abrasive and abrasive

)he numbers ', 2 and 1 designate steel tooth bits and correspond to increasing formatio

hardness.

)he numbers , 5, 3, + and 4 designate bits with tungsten carbide inserts and also

correspond to increasing formation hardness.

soft formations with low compressive strength and high drillability

5 soft to medium formations with low compressive strength

3 medium hard formations with high compressive strength

+ hard semi0abrasive and abrasive formations

4 etremely hard and abrasive formations


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digi


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)he numbers ', 2, 1 and denote a sub0classi"cation of the formation hardness in

each of the eight classes determined by the "rst digit.

)hird digit

' standard roller bearing2 roller bearing, air cooled

1 roller bearing, gage protected

sealed roller bearing

5 sealed roller bearing, gage protected

3 sealed friction bearing

+sealed friction bearing, gageprotected

e"nes the type of bearing and speci"es the presence or absence of gauge

protection by tungsten carbide inserts.

-ourth digit

A air application, ournal bearing bits with air circulation no66les

! special bearing seal, application at high (78

C center et

deviation control9 etended ets

: etra gauge;body protection

/ hori6ontal;steering application

lug pads, pads very close to gage diameter

8 motor application, special design for use on downhole motors

S standard steel tooth model

) two0cone bits, sometimes used for deviation control and penetrationrateW enhanced cutting structure

? chisel tooth insert

@ conical tooth insert other insert shape

5.2.2 rag !it Classi"cation

)he new classi"cation, introduced '*4', also uses fourdigits.


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-irs


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digi


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)h


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e


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letter


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s


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,


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8


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,


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S


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,


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)


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an


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d


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B


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de


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"


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n


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th


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typ


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e


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o


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f


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cutte


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$'


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%


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an


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th


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bod


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y


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material


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atural diamond matri body

8 8atri body 7CS Steel body 7C

) )S7 matri body

B Bther

A new classi"cation uses only 8 for matri and S for steel bodyconstruction.

Second digit

)he numbers ' to * de"ne the bit pro"le, where : denotes gauge hight and C cone

hight respectively.

' : high, C high

2 : high, C medium

1 : high, C low

: medium, C high

5 : medium, C medium

3 : medium, C low

+ : low, C high

4 : low, C medium* :low,Clow

)hird digit

)he numbers ' to * de"ne the hydraulic design

$a% -luid eit $changeable ets, "ed ports, openthroat%,$b% Cutter distribution $bladed, ribbed, open0

faced%,

' changeable ets, bladed

2 "ed ports, bladed

1 open throat, bladed

changeable ets, ribbed

5 "ed ports, ribbed

3 open throat, ribbed


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e letter


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s (


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B ma


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y replac


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e th


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e number


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s


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3 o


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* $tha


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t correspon


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d t


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o mos


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t diamon


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d an


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d )S


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( bits%


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+ changeable ets, open faced4 "ed ports, open face

* open throat, open face


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-ourth digit

)he numbers D to * denote the cutter si6e and density.

D impregnated

' density light, si6e large

2 density medium, si6e large1 density heavy, si6e large

density light, si6e medium

5 density medium, si6e medium

3 density heavy, si6e medium

+ density light, si6e small

4 density medium, si6e small

* density heavy, si6e small

5.1 rill !it Selection and 9valuation

Since a well is drilled only once and each well penetrated the formations at di&erent

locations with di&erent drilling parameters, a selection of a Ebest bitF can not be

performed. )he net best way to "nd an Eoptimum bitF is to compare bit

performances of drilling bits when they were run under similar conditions. )hen a

cost0per0foot value of each bit application can be calculated. Along with this criteria,

the individual bit wear are evaluated. )his knowledge is applied to the well that is to

be drilled $length, inclination, drillability, abrasiveness, etc. of the di&erent sections%.#n practice, when the well is planned, bits that have been used previously in this area

$by this drilling team% are evaluated according to their applicability. Sometimes whena bit manufacturer has developed a new bit he introduces it to the industry with an

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