Patent ID: 8141657

Claim:
A method of controlling a drilling direction of a rotary drill string when drilling boreholes in subsurface formations, said drill string comprising a rotary drill bit at a drilling end thereof and directional control means, adjacent said drill bit, including at least one directional cutting member radially movable with respect to a longitudinal drilling axis of said drill string, said method comprising the steps of: (a) drilling a substantially circular cross section pilot bore hole having a radius determined by a cutting radius of said drill bit of said drill string; and (b) controllably moving the at least one directional cutting member radially, as the drill is rotated, so that a radial position of said cutting member, with respect to the drilling axis, is synchronized with the rotation of said drill bit so that said cutting member continuously engages a wall of said pilot bore hole to enlarge said bore hole as said drill rotates and causing a cross-section of said bore hole to form a non-circular hole superimposed on said pilot hole when it is desired to cause a direction of said advancing drill bit to deviate from a linear path; wherein said directional cutting member is movable between a first radially extended position and a second radially retracted position, with respect to said drilling axis, and said directional cutting member moves between said first radially extended position and said second radially retracted position as said drill string rotates and has a minimum cutting radius in said retracted position greater than the radius of said pilot bore hole.