Page 155 - Drilling Technology in Nontechnical Language

146 Drilling Technology in Nontechnical Language Second Edition

Core Bits

Core bits cut a doughnut-shaped hole, leaving a column of rock sticking

up the middle of the bit (fig. 6–6). Behind the bit is a special tube that holds
this core of rock and recovers it to the surface.
Core bits were mainly diamond bits, though some core bits were
made with a ring of small roller cones and steel teeth. Since PDC bits
were invented, core bits are now predominantly PDC designs, with natural
diamond core bits being used for very hard, abrasive formations.
Core bits often drill faster in the same formation than equivalent
regular bit designs. This may be because they have less rock to cut.

Fig. 6–6. Rock core sample

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