Rotary steerable assembly inhibiting counterclockwise whirl during directional drilling

摘要

A bottom hole assembly avoids damaging vibrations that can develop during directional drilling with a rotary steerable system. The assembly has a drill bit, a first collar that rotates with the bit, a rotary steerable tool that controls the bit's trajectory, and a second collar that rotates with the drill string. The first collar between the bit and the tool defines a bend that deflects the bit from the first collar's axis. During operation, this bend causes portion of the assembly to engage the borehole wall to inhibit counterclockwise (CCW) bit whirl by promoting clockwise whirl in the assembly, generating friction against the borehole wall, and dampening vibrations. By inhibiting CCW bit whirl, other damaging vibrations such as CCW whirl in the drill string can also be prevented up the borehole. Alternatively, only the second collar between the tool and the drill string may define the bend, or both collars can define bends.