Drilling bit 4

©2006ENSPMFormationIndustrie-IFPTraining
CHAPTER 4
BITS CLASSIFICATION

SEC
Roller bits classification
• The current coding system dates back to 1987 and is
made of 4 characters characters (3 digits plus one
letter).
– The First Digit gives information on the type of Cutting
Structure the hardness, the abrasiveness and the
compressive strength of the rocks that can be drilled
with the bit.
• 1, 2 or 3 correspond to milled tooth bits from soft (1),
through medium (2) to hard (3) formations.
• 4 to 8 inclusive are for Tungsten Carbide Insert bits from
4 (soft) to 8 (extremely hard) formations.

SEC
– The Second Digit further defines 4 sub classes, to
smoothen and precise rock strengths from 1 (soft) to 4
(harder).
– The Third Digit defines the type of bearing used and
the presence or the absence of additional gage
protection (special hard-facing of tungsten carbide
inserts) on the back face of the cone:
• 1 Roller Bearings, Open (non sealed) and No gage
protection (common on big diameters)
• 2 Roller Bearings, Open, Non protected, bit designed for
Air Drilling. (in fact, most air drilling bits are gage
protected but still remain inside the #2 class)

SEC
• 3 Roller Bearings, Open, Gage Protected. (common on
12.1/4” bits)
• 4 Roller Bearings, Sealed, Non Gage Protected (very rare,
a nonsense)
• 5 Roller Bearings, Sealed, Gage Protected (common)
• 6 Friction Bearing, Sealed (it has to be), Non Gage
Protected (very rare, not logic, as these designs are
meant to drill longer)
• 7 Friction Bearings, Sealed and Gage Protected
(common)

SEC
– The Letter (fourth position):
• A: Friction bearing designed for air drilling.
• C: Central Jet design.
• D: Directional Drilling bit.
• E: Extended Nozzles (welded tubes)
• G: Reinforced Gage (by either diamond, extra carbide or
special design)
• J: Specially Inclined nozzles.
• R: Specially designed for Percussion.
• S: Standard Steel Tooth bit.
• X: Chisel Shaped Inserts.
• Y: Conical Inserts.
• Z: Other Insert Shape.

SEC
• Examples on how to use of the IADC Code:
– Example 1: The formation to drill is soft to moderately
soft (but rather soft); It has a low compressive strength.
We wish to use an insert bit with friction bearings and
gage protection to improve the bit life and keep the hole
at its nominal diameter…
– The IADC table helps us find the right IADC code for
this application:
• First Digit: Soft to Medium formation with a low
compressive strength and insert type 5
• Second Digit: Soft to rather soft subclass 1 or 2
• Third Digit: Friction Bearings & Gage Protection 7
– This leads to an IADC Code of 517 or 527

SEC

SEC
• Second Example: We have on stock a bit with an IADC
code of 737Y. What the hell is it? The table shows:
– It’s a bit with an insert type cutting structure (1st digit >3)
– Meant to drill hard and semi-abrasive to abrasive
formations (7-3)
– It has friction bearings and carbide gage protection (7)
– The suffix Y indicates inserts are predominantly conical in
shape

SEC
Classification of Fixed Cutter Bits
• Here again, a four character system has been set up.
• Two different Codes apply, depending on the type of
fixed cutter bits:
– PDC bits.
– Natural diamond, TSP and impregnated bits.

SEC
• PDC Bits:
– First Character: Refers to the body material used for the bit
face: (M: matrix or S: steel)
– Second Character: Indicates the Setting (from very light to
heavy) by comparing the PDC count :
• 1 Very Light Set (< 30 PDC) fit for Very soft to Soft Formations
equivalent to 111,115 to137 IADC Code for rollers Bits.
• 2 Light Set (30 to 40 PDC) designed for Soft to Medium Soft
Formations such as 125, 415 to 437 rollers bits equivalent.
• 3 Medium Set (40 to 50 PDC) for Medium Formations equivalent
to 217, 517 to 537 rollers bits class.
• 4 Heavy Set (over 50 PDC) to drill 527 to 537 rollers bits type
Formations (harder end of PDC application)

SEC

SEC
– Third Character refers to PDC size:
• 1 For PDC diameter over 24mm (> ~1”)
• 2 For PDC comprised between 24mm & 14mm
• 3 For PDC size below 14mm but over 8mm
• 4 For 8 mm PDC

SEC
– Fourth Character determines the Bit Profile:
• 1 Fishtail / Flat
• 2 Short Taper or Short Parabolic
• 3 Medium Taper or Medium Parabolic
• 4 Long Taper or Long Parabolic

SEC
• Natural Diamond, TSP & Impregnated Bits:
– First Character refers to the body material used for the
bit face: (M: matrix or S: steel)
– Second Character relates to Stone Size
• 6 Stones bigger than 3 spc. For Medium Hard
Formation equivalent to 537 to 617 Tricone IADC Code
• 7 Stones bigger than 7 spc but smaller than 3 spc. For
Hard Formations equivalent to 627 to 637 of the Tricone
IADC code
• 8 Stones smaller than 7 spc. For formations harder than
Tricone equivalent IADC Code 627

SEC
– Third Character indicates the Type of Cutting Element
• 1 Natural Diamond
• 2 TSP (tripax); Thermally stable Polycrystalline Diamond
• 3 Combination of above
• 4 Diamond Impregnated segments or matrix
– Fourth Character determines the Bit Profile (as for PDC
bits)
• 1 Fishtail / Flat
• 2 Short Taper or Short Parabolic
• 3 Medium Taper or Medium Parabolic
• 4 Long Taper or Long Parabolic

SEC
• Some kind of rules have emerged over the years:
– Bigger PDC are less easy to set to have a smooth
diamond curve, but in the other hand they have a good
brazing area and can stand irregular bottom hole
surfaces (non homogeneous formations).
– Small PDC are more expensive relative to their diamond
content, but fills a profile more smoothly and can be
fixed on thinner blades; In the other hand, they are
easily destroyed when they hit pebbles. (brazing area is
small)
– Oblong Cutters (narrow and
high) can somehow give the best
of the two sizes (coverage and
height) but can prove brittle in
some instances.

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