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(11) | EP 1 008 718 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Rotary drag-type drill bits and methods of designing such bits |
| (57) The invention provides a rotary drag-type drill bit in which the relationship of
torque to rotary bit speed is such that torque generally increases with bit speed.
Such a bit has a reduced tendency to exhibit the phenomenon known as "stick-slip"
while drilling, when compared with bits having a different torque /speed characteristic,
as a result of the positive damping effect of the torque/speed relationship. One method
of designing such a drill bit comprises ascertaining the torque/rotary bit speed relationship,
or other correlated relationships, for a number of different drill bit designs and
then selecting from those designs a design having the desired type of relationship.
Examples of drill bit structures specifically designed to achieve the desired torque/speed
relationship are also disclosed. |