A rotary drill bit assembly suitable for directionally drilling a borehole into an underground formation, the drill bit assembly having a bit body extending along a central longitudinal bit-body axis, and having a bit-body face at its front end, wherein an annular portion of the bit-body face is provided with one or more chip-making elements; a pilot bit extending along a central longitudinal pilot-bit axis, the pilot bit being partly arranged within the bit body and projecting out of the central portion of the bit-body face, the pilot bit having a pilot-bit face provided with one or more chip-making elements at its front end; a joint means arranged to pivotably connect the pilot bit to the bit body so that the bit-body axis and the pilot-bit axis can form a variable diversion angle; and a steering means arranged to pivot the pilot bit in order to steer the direction of drilling.

A downhole drilling subassembly for use with a pressurized fluid carrying drill string extending from a well head and having a portion down a bore hole. A first tubular housing is provided which is adapted to couple to the portion of the drill string in the bore hole. A second tubular housing is carried by the first tubular housing. Each of the housings has a generally circular cross-section and extends along a longitudinal axis. The second tubular housing is longitudinally movable relative to the first tubular housing between a first position at least partially retracted within the first tubular housing and a second position at least partially extended from the first tubular housing. An assembly responsive to moving the second tubular housing from its first position to its second position is carried by the first and second tubular housings for rotating the first and second tubular housings with respect to one another in the bore hole between first and second relative angular positions. The assembly includes a recess provided in one of the tubular housings and formed with a sidewall extending diagonal to the longitudinal axis and a pin carried by the other of the tubular housings and having a portion for travel in the recess.

A downhole drilling subassembly for use with a pressurized fluid carrying drill string extending from a well head down to a bottom of a bore hole. The drill string includes upper and lower sections disposed at an angle relative to each other and having respective upper and lower longitudinal axes. An upper subassembly portion is adapted to couple to the upper section of the drill string. A lower subassembly portion is rotatably carried by the upper subassembly portion and is adapted to couple to the lower section of the drill string. The upper and lower subassembly portions are hollow so as to permit the pressurized fluid to pass therethrough. An assembly responsive to raising the drill string off the bottom of the bore hole and lowering the drill string back onto the bottom of the bore hole is provided for rotating the upper and lower subassembly portions with respect to one another between first and second relative angular positions.

In one aspect of the invention a drill bit assembly has a body portion intermediate a shank portion and a working portion, the working portion having at least one cutting element. A shaft is supported by the body portion and extends beyond the working portion. The shaft also has a distal end that is rotationally isolated from the body portion. In another aspect of the invention, a method for steering a downhole tool string has the following steps: providing a drill bit assembly attached to an end of the tool string disposed within a bore hole; providing a shaft extending beyond a working portion of the assembly; engaging a subterranean formation with a distal end of the shaft; and angling the drill bit assembly with the shaft along a desired drilling trajectory.

In one aspect of the invention a drill bit assembly has a body portion intermediate a shank portion and a working portion, the working portion having at least one cutting element. A shaft is supported by the body portion and extends beyond the working portion. The shaft also has a distal end that is rotationally isolated from the body portion. In another aspect of the invention, a method for steering a downhole tool string has the following steps: providing a drill bit assembly attached to an end of the tool string disposed within a bore hole; providing a shaft extending beyond a working portion of the assembly; engaging a subterranean formation with a distal end of the shaft; and angling the drill bit assembly with the shaft along a desired drilling trajectory.