STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

772 Drilling and Well Completions
TUNGSTEN CARBIDE BIT
wim Sealed Journal BeanngS
-
STEEL TOOTH BIT
wilh Sealed Ball and Roller Bearings
Outer End of Twm
Figure 4-137. Roller (rock) bit elements [45]. (Courtesy Canadian Association
of Oilwell Drilling Contractors.)
each cone and interfitting between rows of teeth on the adjacent cones. The
teeth are either steel and machined as part of the cone, or tungsten carbide
compacts pressed into holes machined in the cone surfaces. The cutters are
mounted on bearings and bearing pins that are an integral part of the bit body.
The size or thickness of the various bit components depends on the type of
formation to be drilled. For instance, soft formation bits generally require light
weights and have smaller bearings, thinner cone shells and thinner bit leg
sections than hard formation bits. This allows more space for long, slender
cutting elements. Hard formation bits, which must be run under heavy weights,
have stubbier cutting elements, larger bearings and sturdier bodies. Shown
in Figure 4-138 are the changes of various bit design factors across the IADC
classification chart.