Geology Reference
In-Depth Information
Figure 4.2.4. Simple rock-bit interaction time traces.
These papers deal with single-tooth impacts, demonstrating that detailed
rock-bit measurements can be made, but it is the net drillbit performance in the
large that is important. Again, many laboratory rig results are available.
Warren's early lab tests, and the work of Grimes, Felderhoff and Brown (1992),
for example, describe how faster penetration rates can be achieved by using
heavy weight rock bits, with special cone, cutter and bearing structures,
designed specifically for drilling with high WOB in hard rock formations.
Finally, Langeveld (1992) provides insight into PDC bit dynamics, explaining
their poor performance in hard formations, and suggesting means for
improvement. He emphasizes the importance of the boundary condition at x = 0
in controlling the dynamics of the entire drillstring, particularly with respect to
its ability to make hole efficiently. Bit design factors, e.g., cutter number and
orientation, play important roles in determining drillstring vibration and
directional characteristics such as “bit walk” and vibration mode coupling.
Controlled tests should be performed for axial, torsional and bending moment
characteristics in order to determine the precise effects of the bits themselves.
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