Steerable drilling system and method

A method of directionally drilling a borehole with a drill string, the method comprising:

• using the drill string to rotate a rotary shaft of a rotary steerable tool, the rotary shaft at least partially disposed in a rigid housing of the rotary steerable tool and coupled to the housing with one or more bearings, the rigid housing having coupled thereto an anti-rotation device to limit the rotation of the housing, the rigid housing having a housing central axis, at least a portion of the shaft capable of rotating about the upper axis while guided by an upper bearing acting between the rigid housing and the rotary shaft, and at least a portion of the shaft capable of being deflected from rotation about the upper axis by a transverse force applied between the rigid housing and the shaft below the upper bearing for rotation about a second rotational axis;
• using a bit below the rotary steerable tool, the bit having a bit face, the bit face having a bit full cutting diameter, and using a gauge section above the bit face, such that the distance from the bit face to a top of the gauge section which is substantially the bit full cutting diameter is at least 75% of the bit full cutting diameter and the top of the gauge section is smaller than the bit full cutting diameter by less than about ¼″;
• and
• deflecting the rotary shaft while drilling the well by applying the transverse force to the rotary shaft in a controllable direction.

A method for directionally drilling a deviated borehole using a bottom hole assembly while rotating a drill string from the surface, the bottom hole assembly comprising:

• a bit having a bit face, the bit face having a bit full cutting diameter;
• a gauge section above the bit, the gauge section having a top end;
• a rotary shaft above the gauge section;
• a housing for a rotary steerable device, the housing having a longitudinal axis, the housing extending from an upper shaft bearing within the housing to a lower end of the housing;
• the rotary shaft extending from the housing, a lower portion of the shaft having a lower central axis offset from the longitudinal axis when drilling a deviated borehole by a transverse force applied to the rotary shaft by a deflection device, an axial spacing between the bit face and an intersection of the longitudinal axis and the lower central axis being less than 12 times the bit diameter;
• wherein the method comprises:
• drilling with the bit, wherein an axial length from the bit full cutting diameter to the top end of the gauge section is at least 75% of the bit full cutting diameter.

A method of using a drill string and a bit having a bit face and a bit full cutting diameter to drill a borehole, comprising:

• providing a stabilizer above the bit, the stabilizer having a gauge section, a portion of which is substantially the bit full cutting diameter, and wherein an axial length between the bit full cutting diameter and a top of the stabilizer gauge portion is at least 75% of the bit full cutting diameter;
• providing a rotary steerable device with a shaft rotatable within a housing having a central axis;
• using an anti-rotation device coupled to the housing to engage the borehole wall;
• using a deflection device to apply a transverse force to the shaft, an axial spacing between the bit face and an intersection of the housing central axis and a lower central axis of a lower portion of the shaft offset from the housing central axis being less than 12 times the bit diameter;
• and
• using the rotary steerable device to directionally steer the bit while rotating the drill string.

A method to use a drill string and a bit having a bit face and a bit full cutting diameter to drill a borehole, comprising:

• providing a stabilizer coupled above the bit, the stabilizer having a gauge section, a portion of which is substantially the bit full cutting diameter, and wherein an axial length between the bit full cutting diameter and a top of the stabilizer gauge portion is at least 75% of the bit full cutting diameter;
• providing above the bit a rotary steerable device comprising a shaft and a rigid housing having a central axis, at least a portion of the shaft to rotate within the rigid housing, the rotary steerable device including a deflection device acting between the rigid housing and the shaft to deflect a lower portion of the shaft, the deflected portion of the shaft having a deflected central axis, the housing being rigid from an upper shaft bearing within the rigid housing to an intersection of the housing central axis and the shaft deflected central axis, and the shaft rotated from above the rotary steerable device;
• and
• using the rotary steerable device to directionally steer the bit while the shaft is rotated from above the rotary steerable device to drill the borehole.

A method to drill a borehole and produce formation evaluation logs, comprising:

• directionally drilling a deviated borehole using a bottom hole assembly (BHA) comprising (a) a bit having a bit face and a bit full cutting diameter;
• (b) a gauge section having a top, the gauge section spaced above the bit face, wherein an axial spacing between the bit face and the top of the gauge section which is substantially the bit full cutting diameter is at least 75% of the bit full cutting diameter;
• and (c) a rotary steerable device above the gauge section to steer the bit while the drill string rotates, the rotary steerable device including a rigid housing extending from an upper shaft bearing within the rigid housing to a deflection device within the rigid housing, the rigid housing having a central axis, the deflection device applying a transverse force to deflect the shaft, a lower portion of the shaft having a shaft central axis offset from the housing central axis, and an axial spacing between the bit face and an intersection of the housing central axis and the shaft central axis being less than 12 times the bit full cutting diameter;
• providing a measurement while drilling (MWD) system within the BHA including one or more sensors to sense one or more of borehole or formation parameters;
• producing a log representing one or more of the borehole or formation parameters.