Page 83 - Air and gas Drilling Field Guide 3rd Edition

74 CHAPTER 4 Downhole Equipment

ROCK ABRASIVENESS
FLAT FACE
HIGHLY
ABRASIVE DOUBLE GAUGE
STEP GAUGE

CONCAVE
DROP CENTER

ROCK
NON- HARDNESS
ABRASIVE
SOFT VERY HARD

FIGURE 4-15. Air hammer bit face profile designs and application to rock formation
abrasiveness and hardness (courtesy of AB Sandvik Rock Tools).

drill bit manufacturers to provide improved air hammer bits for deep drilling
operations. This competition has in turn resulted in an increase in the quality
and durability of air hammer bits (over the traditional air hammer manufacturer-
supplied air hammer bits) in the more hostile environments of the deep bore-
holes. Operational use of the air hammer is discussed in detail in Chapter 11.
These five bit cutting face designs are applicable for a variety of drilling
applications from nonabrasive, soft rock formations to highly abrasive, very hard rock
formations. The applications of these five face designs are shown in Figure 4-15.

4.2.4 Classification of Drill Bits
The International Association of Drilling Contractors (IADC) has approved a stan-
dard classification system for identifying similar bit types available from various
manufacturers [6]. Table 4-1 gives an example IADC numerical classification chart
for insert drill bits (the three digits in the first column).
In general, the classification system adopted is a three-digit code. The first
digit in the bit classification code is the rock formation series number. The letter
“D” precedes the first digit if the bit is a diamond or PDC drag type bit. The first
digit can be the numbers 1 to 3. These are reserved for milled tooth bits for soft,
medium, and hard formation categories, respectively. If the first digit is 5 to 8,
then these are insert bits for soft, medium, hard, and extremely hard formation
categories, respectively.
The second digit is called the type number. Type 0 is reserved for PDC drag
bits. Types 1 to 4 designate formation hardness subclassifications (ranging from
the softest to the hardest formations with each series category).