STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

806 Drilling and Well Completions
The hydraulic design is described by two components: the type of fluid outlet
and the flow distribution. A 3 x 3 matrix of orifice types and flow distributions
defines 9 numeric hydraulic design codes. The orifice type varies from
changeable jets to fixed ports to open throat from left to right in the matrix.
The flow distribution varies from bladed to ribbed to open face from top to
bottom. There is usually a close correlation between the flow distribution and
the cutter arrangement.
The term bladed refers to raised, continuous flow restrictors with a standoff
distance from the bit body of more than 1.0 in. In most cases cutters are affixed
to the blades so that the cutter arrangement may also be described as bladed.
The term ribbed refers to raised continuous flow restrictors with a standoff
distance from the bit body of 1.0 in. or less. Cutters are usually affixed to most
of the ribs so that the cutter arrangement may also be described as ribbed. The
term open fuce refers to nonrestricted flow arrangements. Open face flow designs
generally have a more even distribution of cutters over the bit face than with
bladed or ribbed designs.
A special case is defined the numbers 6 and 9 describe the crowfoot/water
course design of most natural diamond and many TSP bits. Such designs are
further described as having either radial flow, crossf low (feeder/collector), or
other hydraulics. Thus, the letters R (radial flow), X (crossflow), or 0 (other)
are used as the hydraulic design code for such bits.
Cutter Size and Placement Density. The numbers 1 through 9 and 0 in the
fourth character of the fixed cutter classification code refer to the cutter size
and placement density on the bit (Figure 4-161). A 3 x 3 matrix of cutter sizes
and placement densities defines 9 numeric codes. The placement density varies
from light to medium to heavy from left to right in the matrix. The cutter size
varies from large to medium to small from top to bottom. The ultimate
combination of small cutters set in a high density pattern is the impregnated
bit, designated by the number 0.
Cutter size ranges are defined for natural diamonds based on the number of
stones per carat. PDC and TSP cutter sizes are defined based on the amount
of usable cutter height. Usable cutter height rather than total cutter height is
the functional measure since various anchoring and attachment methods affect
the “exposure” of the cutting structure. The most common type of PDC cutters,
which have a diameter that is slightly more than + in., were taken as the basis
for defining medium size synthetic diamond cutters.
Cutter density ranges are not explicitly defined. The appropriate designation
is left to the judgment of the manufacturer. In many cases manufacturers
build “light-set” and “heavy-set” versions of a standard product. These can be
distinguished by use of the light, medium, or heavy designation which is
encoded in the fourth character of the IADC fixed cutter bit code. As a general
guide, bits with minimal cutter redundancy are classified as having light
placement density and those with high cutter redundancy are classified as having
heavy placement density.
Examples of Fixed-Cutter Bits Classification
Figure 4-162 shows a natural diamond drill bit which has a long outer taper
and medium inner cone, radial flow fluid courses, and five to six stones per
carat (spc) diamonds set with a medium placement density. Using the definitions
in Figures 4-156, 4-158, 4-159, and 4-160, the characteristics of this bit are coded
D 2 R 5 as follows: