The rigid link that exists between the bit and the bottomhole assembly
(BHA) is responsible for initiating severe downhole vibrations. Intro
duction of a tilt flexibility at the bit allows the decrease of the co
upling between the bit and the BHA, hence improving the bit stability.
The concept has been verified with a specially designed laboratory ma
chine capable of creating downhole dynamic conditions. An 81/2-in. bit
prototype has been designed and tested in the field. Downhole acceler
ometer records demonstrate that the vibration level can be substantial
ly lowered by the introduction of a flexible connection at the bit.