Wednesday, 15 November 2017


The IADC Classification System For Fixed Cutter Bits (PDC) 

PDC Bits History

Polycrystalline diamond materials, for use in polycrystalline diamond compact (PDC) bits, are one of the most important material advances for oil drilling tools in recent years. Fixed-head bits rotate as one piece and contain no separately moving parts. When fixed-head bits use PDC cutters, they are commonly called PDC bits. Since their first production in 1976, the popularity of bits using PDC cutters has grown steadily, and they are nearly as common as roller-cone bits in many drilling applications.

What is IADC PDC Drill Bits Classification System?

The IADC PDC Bit Classification system, developed by the International Association of Drilling Contractors has been the representative voice of drillers worldwide since 1940. This system has enabled drillers worldwide to exchange information using standard nomenclature and dull grading methods for PDC drill bits and tricones. This system is not as widely used for PDC drill bits as it is for tricones as the IADC system for tricones is used the world over. However, it’s helpful to have a knowledge of the IADC classification system for PDC drill bits.

How To Classify PDC Drill Bits Using IADC Classification System?

IADC PDC Drill Bits Classification System Codes are consists from 4 characters:

The First Character Of IADC PDC Drill Bit Codes

The first letter of the IADC Classification Code For PDC Bit describes the body material and it is either: 

1) M which is for matrix body 
“Matrix” is a very hard, rather brittle composite material comprising tungsten carbide grains metallurgically bonded with a softer, tougher, metallic binder. Matrix is desirable as a bit material, because its hardness is resistant to abrasion and erosion. It is capable of withstanding relatively high compressive loads, but, compared with steel, has low resistance to impact loading.

2) S for steel body construction.
Steel is metallurgically opposite of matrix. It is capable of withstanding high impact loads, but is relatively soft and, without protective features, would quickly fail by abrasion and erosion. Quality steels are essentially homogeneous with structural limits that rarely surprise their users

The Second Character Of IADC PDC Drill Bit Codes

    Diamond is the hardest material known. This hardness gives it superior properties for cutting any other material. PDC is extremely important to drilling, because it aggregates tiny, inexpensive, man-made diamonds into relatively large, intergrown masses of randomly oriented crystals that can be formed into useful shapes called diamond tables. The second letter of the IADC Classification Code For PDC Bit describes the cutter density. As it is known as more you increase the number of PDC cutter as more The PDC bit can drill harder formations. (refer to PDC Bit Design Article for more informations).

    This IADC Code character ranges from 1 to 4 for PDC bits and from 6 to 8 for Diamond bits as below. 
    • For PDC bits : ranges from 1 for soft formations to 4 for hard formation
      • 1 refers to 30 or fewer 1/2” cutters
      • 2 refers to 30 to 40 cutters
      • 3 indicates 40 to 50 cutters
      • refers to 50 or more cutters.
    • For diamond bits : ranges from 6 for soft formations to 8 for hard formation
      • 6 refers to diamond sizes larger than 3 stones per carat 
      • 7 refers to  3 stones to 7 stones per carat
      • 8 refers to sizes smaller than 7 stones per carat. 
    • Numerals 0, 5 and 9 are reserved for future use. 

    The Third Character Of IADC PDC Drill Bit Codes

    As a general rule, large PDC cutters sizes  (19mm to 25mm) are more aggressive than small cutters. However, they may increase torque fluctuations. Smaller PDC cutters sizes (8mm, 10mm, 13mm and 16mm) have been shown to drill at higher ROP than large cutters in certain applications. One such application is limestone for example. (refer to PDC Bit Design Article for more informations)

    Additionally, small cutters produce smaller cuttings while large cutters produce larger cuttings. Large cuttings may cause problems with hole cleaning if the drilling fluid cannot carry the cuttings up.

    The third letter of the IADC Classification Code For PDC Bit describes the size of cutter.
    • For PDC bits
      1 indicates cutter larger than 24 mm in diameter  clay, marl, gumbo and unconsolidated sands.
      2 represent 14-24 mm,
      3 indicates 13.3 mm (1/2”), and
      4 is used for the smaller 8 mm in diameter. 
    The third letter of the IADC Classification Code For Diamond Bit describes the type of cutter. 
    • For diamond bits: the third digit represents diamond type
      1 indicating natural diamonds
      2 to TSP material
      3 represents mixed natural diamonds and TSP
      4 applies only to the highest density bit, indicating an impregnated diamond bit.

    The Fourth Character Of IADC PDC Drill Bit Codes

    The Fourth Character Of IADC PDC Drill Bit Codes gives the basic description of bit’s profile. Bit profile affects both cleaning and stability of the PDC bit. The two most widely used profiles are: Double cone & Shallow cone (refer to PDC Bit Design Article for more informations)

    This fourth letter of IADC code ranges from 1 to 4 which:
    1 represents both fishtail PDC bit and ‘flat’ TSP and natural diamond bits.
    2 & 3 & 4 indicate increasingly longer bit profiles

    Classification Of Diamond Bits
    Classification Of Diamond Bits

    Useful Papers For IADC PDC Bits Classification System

     PDC Bit Classification According to Steerability

    Paper Abstract: With the emergence of rotary steerable systems (RSSs), the technical issue concerning bit design for a specific directional application has reappeared. Today, a bit must be specifically designed for use with a particular directional system: rotary bottomhole assembly (BHA), steerable mud motor, or RSS. The reason is that the bit must have the ability to respond properly and rapidly to a side force applied by the steering system to initiate a deviation. To do so, the bit must have a predetermined steerability compatible with the directional system to provide the optimum dogleg potential. The new generation of directional-drilling systems differentiates "pointing the bit" from "pushing the bit." As a consequence, the bit's directional response is a key factor that operators and directional drillers need to know to make a good adaptation between the bit and the BHA. However, at the moment there is no standard method for classifying bits by steerability and walking tendency. On the basis of a comprehensive analysis of the directional behavior of polycrystalline diamond compact (PDC) bits (numerical simulation and pilot and field tests), a simple methodology has been developed that defines and evaluates their steerability and walking tendency. This methodology is used to classify the PDC bits defined with their IADC bit profile codes. Because PDC bit steerability is mainly a function of the bit profile, the gauge cutters, and the gauge pad, some design recommendations are given concerning these three parts. For each IADC bit profile code, the bit steerability and walking tendency are estimated through some formulas linking only the heights and lengths of the cutting profile. Some guidelines are also given about the gauge-pad length and gauge-cutter characteristics to achieve improved steerability. This simple method based on geometrical criteria allows quick estimation of not only the PDC bit steerability but also the maximum dogleg potential achievable by the bit when it is coupled with the steering system.