FLEXIBLE BIT : A NEW ANTIVIBRATION PDC-BIT CONCEPT

The rigid link that exists between the bit and the bottomhole assembly (BHA) is responsible for initiating severe downhole vibrations. Introduction of a tilt flexibility at the bit allows the decrease of the coupling between the bit and the BHA, hence improving the bit stability. The concept has been verified with a specially designed laboratory machine capable of creating downhole dynamic conditions. An 8 1/2-in. bit prototype has been designed and tested in the field. Downhole accelerometer records demonstrate that the vibration level can be substantially lowered by the introduction of a flexible connection at the bit.