Drilling bit 4

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Formation Industrie -IFP

Training

CHAPTER 4 BITS CLASSIFICATION

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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.

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– 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)

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• 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)

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– 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.

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• 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

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• 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

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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.

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• 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)

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– 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

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– 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

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• 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

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– 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

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Classification of Fixed Cutter Bits• 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.

Engineering

Drilling bit 4