STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

~ ~~ ~~ ~ ~ ~ ~ ~~ ~~~~
Drilling Bits and Downhole Tools 771
Table 4-91
Roller Bit Additional Design Feature [44]
Code Feature Code Feature
A Air application' N
B 0
C Centerjet P
D Deviation control Q
E Extended jets R Reinforced welds2
F S Standard steel tooth model3
G Extra gaugebody protection T
H
U
I
V
J Jet deflection W
K X Chisel insert
L Y Conical insert
M Z Other insert shape
'Journal bearing bits with air circulation nozzles
2For percussion applications
3Milled tooth bits with none of the extra features listed in this table
Courtesy SPE
Additional Features. Additional features are important since they can affect
bit cost, applications and performance. The fourth character of the IADC code
is used to indicate additional features. Eleven such alphabetic characters are
presently defined as shown in Table 4-91 [44]. Additional alphabetic characters
may be utilized as required by future roller bit designs. Although the fourth
character does not appear on the IADC bit comparison chart, it appears everywhere
else that the IADC code is recorded such as on the shipping container
and bit record.
The IADC code should be interpreted as shown in the following examples:
(1) 124E-a soft formation, sealed roller bearing milled tooth bit with extended
jets, (2) 437X-a soft formation, sealed friction bearing insert bit, with gauge
protection and chisel-shaped teeth.
Some bit designs may have a combination of additional features. In such cases
the manufacturer selects the most significant feature for the fourth character
of the classification code.
IADC publishes the current bit classification charts for nearly all of the major
roller bit manufacturers. In addition, IADC publishes reference charts for
"obsolete" bits that are no longer available. These are useful when reviewing
older bit records in order to plan a well.
The current IADC classification charts for seven roller bit manufacturers are
shown in Ref. [44].
Bit classification is general and is to be used simply as a guide. All bit
types will drill effectively in formations other than those specified. It is the
responsibility of the manufacturer to classify his bits at his or her own discretion.
Roller Rock Bit Design
The elements of the roller rock bit are shown in Figure 4-137 [45]. Roller
rock bits have three major components: the cone cutter, the bearings and the
bit body. The cutting elements are circumferential rows of teeth extending from