Page 153 - Drilling Technology in Nontechnical Language

144 Drilling Technology in Nontechnical Language Second Edition

Fig. 6–3. PDC cutter

PDC and diamond bits are made in many different shapes. The shape of

a bit will influence whether the bit can be easily made to drill directionally
or whether it will tend to drill straight ahead. The shape also affects how
many cutters can be mounted on the bit (due to the different surface area).

Examples of two extremes are shown in figure 6–4. The bit to the left has
cutters mounted on the side. Combined with its slightly concave, almost

flat profile, this bit cuts sideways easily. The parabolic profile bit on the

right will be much more stable directionally.
One other type of fixed cutter bit should be mentioned. In the early

days of the oil well drilling industry, the drill bit was made from steel and
was resharpened at the wellsite by a blacksmith. These bits resemble a
fish’s tail when viewed from the side and thus were called fi shtail bits (see

fig. 6–5). They work by scraping the rock and were only suitable for soft

formations. It was not until the advent of the roller cone drill bit (invented
by Howard Hughes and patented in 1909) that the capability of drill bits
extended to drilling at greater depths and harder rock.

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