STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Drilling Bits and Downhole Tools 801
Figure 4-155. Cutter orientation [43A]. (Courtesy Hughes Christensen.)
IADC Fixed Cutter Bit Classification System
The term fixed cutter is used as the most correct description for the broad
category of nonroller cone rock bits. The cutting elements may be comprised
of any suitable material. To date, several types of diamond materials are used
almost exclusively for fixed cutter petroleum drilling applications. This leads to
the widespread use of the term “diamond” bits and PDC bits in reference to
fixed cutter designs.
The IADC Drill Bits Subcommittee began work on a new classification method
in 1985. It was determined from the outset that (1) a completely new approach
was required, (2) the method must be simple enough to gain widespread
acceptance and uniform application, yet provide sufficient detail to be useful,
(3) emphasis should be placed on describing the form of the bit, i.e., “paint a
mental picture of the design”, (4) no attempt should be made to describe the
function of the bit, i.e., do not link the bit to a particular formation type or
drilling technique since relatively little is certain yet about such factors for fixed
cutter bits, (5) every bit should have a unique IADC code, and (6) the classification
system should be so versatile that it will not be readily obsolete.
The resultant four-character diamond bit classification code was formally
presented to the IADC Drilling Technology Committee at the 1986 SPE/IADC
Drilling Conference. It was subsequently approved by the IADC Board of
Directors and designated to take effect concurrent with the 1987 SPE/IADC
Drilling Conference. A description of the 1987 IADC Fixed Cutter Bit Classification
Standard follows [54].
Four characters are utilized in a prescribed order (Figure 4-156) to indicate
seven fixed cutter bit design features: cutter type, body material, bit profile, fluid
discharge, flow distribution, cutter size, and cutter density. These design traits
were selected as being most descriptive of fixed cutter bit appearance.
The four-character bit code is entered on an IADC-API Daily Drilling Report
Form as shown in Figure 4-157. The space requirements are consistent with the
four-character IADC roller bit classification code. The two codes are readily
distinguished from one another by the convention that diamond bit codes begin
with a letter, while roller bit codes begin with a number.
Each of the four characters in the IADC fixed cutter bit classification code
are further described as follows:
Cutter TLpe and Body Material. The first character of the fixed cutter classification
code describes the primary cutter type and body material (Figure 4-156).