An apparatus and method to control the rotation of a downhole drill bit are disclosed. A pair of spaced-apart measuring or survey instruments at the drill string provide data that is analyzed to determine relative rotation between the instruments so that drag affecting the drill bit may be reduced....http://www.google.fr/patents/US7798246?utm_source=gb-gplus-shareBrevet US7798246 - Apparatus and method to control the rotation of a downhole drill bit
Apparatus and method to control the rotation of a downhole drill bit
