Directional drilling control using periodic perturbation of the drill bit

[0021]Disclosed herein are devices and methods for steering the direction of a borehole advanced by cutting action of a rotary drill bit.

[0022]Directional drilling is obtained by periodically perturbing the action of the drill bit. For purposes of this disclosure “periodic variation” is defined as varying the drill bit rotation speed and / or rate of penetration (ROP) in a plurality of 360-degree drill string rotations or “cycles” at the same azimuthal arc in the plurality of rotations.

Hardware

[0023]Attention is directed to FIG. 1, which illustrates a borehole assembly (BHA) 10 suspended in a borehole 30 defined by a wall 50 and penetrating earth formation 36. The upper end of the BHA 10 is operationally connected to a lower end of a drill pipe 35 by means of a suitable connector 20. The upper end of the drill pipe 35 is operationally connected to a rotary drilling rig, which is well known in the art and represented conceptually at 38. Surface casing 32 extends from the borehole 30 to...