Abstract: A stabilizer especially adapted for use with an drill string having an eccentric drilling element, such as a bi-center bit. The stabilizer has a pair of circumferentially displaced blades that lie in a common circumferential plane and extend from a rotatable sleeve supported on the stabilizer body, as well as a stationary blade. The rotating blades are aligned with the stationary blade when in a first circumferential orientation and are disposed so that the mid-point between the rotating blades is located opposite the stationary blade, thereby providing full-gauge stabilization, when the rotating blades are in a second circumferential orientation. A magnetic systems senses the circumferential orientation of the rotating blades and transmits the information to the surface via mud pulse telemetry. A piston actuated by the drilling mud locks the rotating blades into the active and inactive positions.

Abstract: A stabilizer for a drill string and drill bit is mounted behind the drill bit in the drilling assembly. The stabilizer comprises a tubular body having one or more stabilizer blades mounted thereon. The stabilizer blades extend radially outwardly from the stabilizer body. In a first position, the stabilizer blades are in vertical axial alignment behind the drill bit. Drill string pressure is utilized to release a locking mechanism permitting relative rotation between the stabilizer blades and the stabilizer body thereby rotating the stabilizer blades to a second position providing stabilization for the drill string and drill bit.