Patent Publication Number: US-8522897-B2

Title: Lead the bit rotary steerable tool

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Patent Application is a continuation-in-part of U.S. patent application Ser. No. 12/362,661 filed on Jan. 30, 2009, which is a continuation-in-part of U.S. patent application Ser. No. 11/837,321 filed on Aug. 10, 2007 and that issued as U.S. Pat. No. 7,559,379 on Jul. 14, 2009, which is a continuation-in-part of U.S. patent application Ser. No. 11/750,700 filed on May 18, 2007 and that issued as U.S. Pat. No. 7,549,489 on Jun. 23, 2009, which is a continuation-in-part of U.S. patent application Ser. No. 11/737,034 filed on Apr. 17, 2007 and that issued as U.S. Pat. No. 7,503,405 on Mar. 17, 2008, which is a continuation-in-part of U.S. patent application Ser. No. 11/686,638 filed on Mar. 15, 2007 and that issued as U.S. Pat. No. 7,424,922 on Sep. 16, 2008, which is a continuation-in-part of U.S. patent application Ser. No. 11/680,997 filed on Mar. 1, 2007 and that issued as U.S. Pat. No. 7,419,016 on Sep. 2, 2008, which is a continuation-in-part of U.S. patent application Ser. No. 11/673,872 filed on Feb. 12, 2007 and that issued as U.S. Pat. No. 7,484,576 on Feb. 3, 2009, which is a continuation-in-part of U.S. patent application Ser. No. 11/611,310 filed on Dec. 15, 2006 and that issued as U.S. Pat. No. 7,600,586 on Oct. 13, 2009. The U.S. patent application Ser. No. 11/837,321 is a continuation-in-part of U.S. patent application Ser. No. 11/278,935 filed on Apr. 6, 2006 and that issued as U.S. Pat. No. 7,426,968 on Sep. 23, 2008, which is a continuation-in-part of U.S. patent application Ser. No. 11/277,394 filed on Mar. 24, 2006 and that issued as U.S. Pat. No. 7,398,837 on Jul. 15, 2008, which is a continuation-in-part of U.S. patent application Ser. No. 11/277,380 filed on Mar. 24, 2006 and that issued as U.S. Pat. No. 7,337,858 on Mar. 4, 2008, which is a continuation-in-part of U.S. patent application Ser. No. 11/306,976 filed on Jan. 18, 2006 and that issued as U.S. Pat. No. 7,360,610 on Apr. 22, 2008, which is a continuation-in-part of U.S. patent application Ser. No. 11/306,307 filed Dec. 22, 2005 and that issued as U.S. Pat. No. 7,225,886 on Jun. 5, 2007, which is a continuation-in-part of U.S. patent application Ser. No. 11/306,022 filed on Dec. 14, 2005 and that issued as U.S. Pat. No. 7,198,119 on Apr. 3, 2007, which is a continuation-in-part of U.S. patent application Ser. No. 11/164,391 filed on Nov. 21, 2005 and that issued as U.S. Pat. No. 7,270,196 on Sep. 18, 2007. All of these applications are herein incorporated by reference in their entirety and their priorities claimed. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to the field of tools used in directional drilling. More specifically, the invention includes a flexible portion disposed in a drill string to facilitate drilling inclined wellbores. The prior art includes several methods for steering a tool string. An embodiment of a bent sub system is generally depicted in  FIG. 1   a . In this embodiment, a drill string  2000  comprises a bent sub  2050  above the drill bit  2051 . A hydraulic motor housed within a bore of a drill string component rotates the drill bit  2051  below the bent sub  2050 . As drilling mud is passed through the drill string  2000 , the motor turns in response to the flow and rotates a portion  2052  of the drill string  2000  below the bent sub  2050 . A portion  2053  of the drilling string  2000  above the bent sub  2050  does not rotate from the motor, but slides through the wellbore as the drill bit  2051  advances into the earth. The bent sub  2050  directs the trajectory of the drill string  2000  in relation to an angle of the bent sub  2050 . 
     An embodiment of a push-the-bit system is generally depicted in  FIG. 1   b . In this embodiment of a drill string  2100 , an extendable pad  2150  is located above the drill bit  2151 . Typically, there is more than one extendable pad oriented around an outer surface of the drill string  2100  near the drill bit  2151  that are timed together so as to extend at the same azimuth with relation to the well bore while the drill string  2100  is rotating. Each time an extendable pad  2150  extends, it pushes the drill bit  2151  off course and may be used to control the trajectory of the drill string  2100 . 
     Yet another embodiment for steering a bit includes point-the-bit systems where a drill bit is actively positioned from further up a drill string. 
     Variations of these systems are disclosed in the following prior art documents. U.S. Pat. No. 5,529,133 to Eddison, which is hereby incorporated by reference for all that it contains, discloses a steerable rotary drilling tool that includes a drill bit mounted on the lower end of a housing by a drive shaft having an articulative coupling that allows the bit&#39;s rotation axis to be inclined relative to the rotation axis of the housing, an eccentric weight in the housing that maintains the bit axis pointed in only one direction in space as the bit is turned by the housing, and a clutch system that allows such direction to be changed downhole. A measuring-while-drilling tool is included to allow the progress of the drilling to be monitored at the surface and to allow changing the bit axis or toolface by a selected amount. 
     U.S. Pat. No. 5,078,650 to Foote which is herein incorporated by reference for all that it contains discloses a universal joint arrangement that includes a first adapter having two projecting support formations; a drive plate having a first pair of matching depressions or pockets is seated with these depressions on the projecting support formations of the first adapter and the drive plate has a second pair of pockets for the projecting support formations of a respective second adapter. 
     U.S. Pat. No. 7,188,685 to Downton which is herein incorporated by reference for all that it contains discloses a bottom hole assembly that is rotatably adapted for drilling directional boreholes into an earthen formation. It has an upper stabilizer mounted to a collar, and a rotary steerable system. The rotary steerable system has an upper section connected to the collar, a steering section, and a drill bit arranged for drilling the borehole attached to the steering section. The steering section is joined at a swivel with the upper section. The steering section is actively tilted about the swivel. A lower stabilizer is mounted upon the steering section such that the swivel is intermediate the drill bit and the lower stabilizer. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect of the present invention, a drilling assembly includes a drill bit body disposed intermediate a working face and a shank. The shank may be attached to a drill string. The working face comprises an indenting member protruding from the working face, the indenting member being adapted to guide the drill bit. A flexible portion is disposed above the bit body to allow angular deflection of the bit with respect to the drill string. 
     The flexible portion may comprise upper and lower segments, and may be disposed intermediate, or between, the bit body and the shank or may be disposed intermediate, or between, the shank and an adjacent drill string component. The lower segment of the flexible portion may comprise an extension with a generally spherical distal end, and a corresponding spherical recess may be disposed in the upper segment. Bearing balls adapted to transfer torque may be retained in recesses and/or grooves in the spherical portions of the upper and lower segments. In another embodiment, the flexible portion may comprise one or more universal joints. The flexible portion may comprise a compliant segment. The flexible portion may comprise a joint with laterally sliding surfaces. 
     The indenting member may be rotatable with respect to the bit body. A shaft may be disposed internal to the bit body and intermediate the indenting member and a rotating element such as a fluid-driven turbine, mud motor, or an electric motor. The shaft may be flexible, and may comprise a compliant portion, one or more universal joints, or a constant velocity joint. 
     The indenting member may comprise asymmetrical geometry on a distal end and a polycrystalline diamond cutting element. The polycrystalline diamond cutting element may comprise a pointed geometry. 
     The drilling assembly may comprise a mechanism adapted to selectively prevent movement of the flexible portion for drilling straight wellbores. The mechanism may be adapted to selectively limit angular deflection of the flexible portion, and may self-align the flexible portion to a position of zero angular deflection. 
     The drilling assembly may comprise a wiper seal disposed intermediate moveable sections of the flexible portion. The drilling assembly may also comprise a bellows-type seal disposed exterior to the flexible portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a  is a cross-sectional view of an embodiment of the prior art. 
         FIG. 1   b  is a cross-sectional view of another embodiment of the prior art. 
         FIG. 1   c  is a cross-sectional view of an embodiment of a drill string suspended in a borehole. 
         FIG. 2  is a cross-sectional view of an embodiment of a drilling assembly. 
         FIG. 3  is a cross-sectional view of another embodiment of a drilling assembly. 
         FIG. 4  is a different cross-sectional view of the embodiment of a drilling assembly in  FIG. 3 . 
         FIG. 5  is a cross-sectional view of another embodiment of a drilling assembly. 
         FIG. 6  is a perspective view of an embodiment of a universal joint. 
         FIG. 7   a  is a cross-sectional view of another embodiment of a drilling assembly. 
         FIG. 7   b  is a different cross-sectional view of the embodiment of a drilling assembly in  FIG. 7   a.    
         FIG. 8   a  is a perspective view of an embodiment of an indenting member. 
         FIG. 8   b  is a perspective view of another embodiment of an indenting member. 
         FIG. 8   c  is a perspective view of another embodiment of an indenting member. 
         FIG. 8   d  is a perspective view of another embodiment of an indenting member. 
         FIG. 9  is a cross-sectional view of another embodiment of a drilling assembly. 
         FIG. 10   a  is a cross-sectional view of another embodiment of a drilling assembly. 
         FIG. 10   b  is another cross-sectional view of the embodiment of a drilling assembly in  FIG. 10   a.    
         FIG. 10   c  is a detailed view of the embodiment of a drilling assembly in  FIG. 10   a.    
         FIG. 11   a  is a cross-sectional view of another embodiment of a drilling assembly. 
         FIG. 11   b  is another cross-sectional view of the embodiment of a drilling assembly in  FIG. 11   a.    
         FIG. 12  is a cross-sectional view of another embodiment of a drilling assembly. 
         FIG. 13  is a cross-sectional view of another embodiment of a drilling assembly. 
         FIG. 14  is a cross-sectional view of another embodiment of a drilling assembly. 
         FIG. 15  is a diagram of an embodiment of a steering method. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENT 
       FIG. 1   c  discloses a drill string  100  suspended in a borehole  103  by a derrick  101 . A drilling assembly  102   a  is connected to the end of the drill string  100  and comprises a drill bit  104   a . As the drill bit  104   a  rotates the drill string  100  advances in the formation  105   a . The drill string  100  may comprise one or more flexible portions  209   a  to allow directional drilling. 
       FIG. 2  discloses an embodiment of a drilling assembly  102   b . The drilling assembly  102   b  may comprise a drill bit  104   b  with a working face  106   a , an indenting member  107   a  protruding from the working face  106   a , and a shank  108   a . A compliant segment  113  may be disposed intermediate, or between, the shank  108  and a portion of the drill string  109   a . The compliant segment  113  may comprise a portion of reduced cross-section  110  to provide elastic angular deflection with respect to an axial centerline of the portion of the drill string  109   a . Cross-sectional area may be reduced by a taper, a series of circumferential or axial grooves, or one or more helical grooves or via a more elastic material. The compliant segment  113  may be constructed from any material with sufficient strength and suitable elastic modulus, such as high-strength steel or other metal or metal alloy. The drilling assembly  102   b  may comprise a shaft  111   a  intermediate, or between, the indenting member  107   a  and a rotating element  114   a  such as a fluid powered turbine, mud motor or an electric motor. The shaft  111   a  may comprise a compliant portion  112   a  to allow deflection in the shaft  111   a  corresponding to the deflection in the compliant segment  113 . 
     The indenting member  107   a  may be asymmetric such that as it indents into the formation it leads the drill bit  104   b  away from a straight trajectory. The rotating element  114   a  above may be used to position an apex of the indenting member  107   a  at a desired azimuth for the drill string  109   a  to follow. In such a manner, the driller may control the trajectory of the drill string  109   a . In some embodiments, it may be desirable for the drill string  109   a  to drill in a straight trajectory; in such cases, the indenting member  107   a  may be randomly or otherwise rotated such that it leads the drill bit  104   b  in a straight direction. 
     The ability of the indenting member  107   a  to steer depends on the ability of the asymmetric indenting member  107   a  to push off of the formation. In soft formations, the formation may push back on the indenting member  107   a  less. Thus, the compliant portion  112   a  may lower the amount of formation side push back on the indenting member  107   a  required to alter the path of the drill bit  104   b.    
       FIG. 3  discloses a drilling assembly  102   b  according to the present invention. The drilling assembly  102   b  may comprise a drill bit  104   c  with a working face  106   b , an indenting member  107   b  protruding from the working face  106   b , and a shank  108   b . The shank  108   b  is connected to a flexible portion  209   a . The flexible portion  209   a  comprises an upper segment  210   a  and a lower segment  211   a , the lower segment  211   a  comprising an extension  212   a  with a generally spherical portion  213 . The upper segment  210   a  comprises a generally spherical recess  214  corresponding to the generally spherical portion  213  of the lower segment  211   a . The generally spherical portion  213  is moveably retained in the generally spherical recess  214 . The generally spherical recess  214  comprises a plurality of reliefs  215  which hold a plurality of bearing balls  216 . The generally spherical portion  213  of the lower segment  211   a  comprises a plurality of grooves  217 , the bearing balls  216  extending into the grooves  217 . The bearing balls  216  are free to slide or rotate in the grooves  217  and reliefs  215 , thus allowing angular deflection of the lower segment  211   a  with respect to the upper segment  210   a , while providing torque transmission through the flexible portion  209   a  as the drilling assembly  102   b  rotates. The bearing balls  216  may be retained in a bearing cage. The bearing balls  216  may be constructed from high strength steel and may be case hardened, heat treated, or otherwise processed to provide sufficient strength. Other suitable materials such as other metals, metal alloys, or ceramic may be used. The reliefs  215  and grooves  217  that retain the bearing balls  216  may also be heat treated, case hardened, or otherwise processed to mitigate abrasive wear. 
     The upper segment  210   a  may comprise a mechanism that selectively prevents movement of the lower segment  211   a  with respect to the upper segment  210   a . In this embodiment, a plurality of stops  219   a  are disposed inside the upper segment  210   a  and may be brought into contact with the lower segment  211   a , thus preventing angular deflection of the flexible portion  209   a  and allowing the drilling assembly  102   b  to drill a straight borehole. The plurality of stops  219   a  may be actuated by a mechanical, hydraulic, or electronic system or combinations thereof. 
     The upper segment  210   a  of the flexible portion  209   a  comprises a face  220  with a convex, generally spherical geometry, and the lower segment  211   a  comprises a face  221  with a concave, generally spherical geometry. The faces  220 ,  221  on the upper segment  210   a  and the lower segment  211   a , respectively, have a common, substantially constant radius of curvature, with a center of curvature in the same location as a center of curvature of the generally spherical portion  213  and the generally spherical recess  214 . The faces  220  and  221  are in slideable contact, thus allowing angular deflection of the lower segment  211   a  with respect to the upper segment  210   a . The faces  220  and  221  may be heat treated, case hardened, or coated with a wear resistant material such as polycrystalline diamond, a low-friction material such as PTFE, or other wear resistant and/or low friction coating. 
     The drilling assembly  102   b  may also comprise a shaft  111   b  intermediate, or between, the indenting member  107   b  and a rotating element  114   b , such as a fluid-powered turbine or electric motor. The shaft  111   b  may comprise a compliant portion  112   b  to allow deflection corresponding to the deflection of the flexible portion  209   a.    
     Referring now to  FIG. 4 , the plurality of stops  219   a  are removed from contact with the lower segment  211   a , thus allowing greater angular deflection  401  of the lower segment  211   a  with respect to the upper segment  210   a . The indenting member  107   b  may comprise an asymmetrical geometry  402  on a distal end  803   a . As the drilling assembly  102   b  rotates, the rotating element  114   b  rotates the shaft  111   b  with an angular velocity having the same magnitude but opposite direction of the angular velocity of the drilling assembly  102   b . Thus, the indenting member  107   b  has zero angular velocity with respect to the formation  105   b , and the asymmetrical geometry  402  on the distal end  803   a  guides the drill bit  104   c  through the formation  105   b  in an azimuth direction determined by the orientation of the indenting member  107   b.    
     In some embodiments the flexible portion  209   a  is moved passively in consequence of the deflections caused by the indenting member  107   b.    
     The plurality of stops  219  may selectively constrain the angular deflection  401  of the flexible portion  209   a  to any angle in an interval including zero angle, or non-deviated drilling, to the maximum angle attainable by the flexible portion  209   a.    
       FIG. 5  discloses another embodiment of a drilling assembly  102   c  according to the present invention. In this embodiment, the drilling assembly  102   c  comprises a drill bit  104   d  comprising a working face  106   c  and a shank  108   c . A flexible portion  209   b  is disposed intermediate, or between, the working face  106   c  and the shank  108   c . The shank  108   c  is connected to a drill string  501 . 
       FIG. 6  discloses an embodiment of a universal joint  601 . The universal joint  601  comprises an inner portion  602  and an outer portion  603 . The inner portion  602  is attached to the outer portion  603  by a spider  604   a  comprising bearing carriers  605   a.    
     Referring now to  FIG. 7   a , a drilling assembly  102   d  comprises a drill bit  104   e  with a working face  106   d  and a shank  108   d . The drill bit  104   e  comprises a flexible portion  209   c  intermediate, or between, the working face  106   d  and the shank  108   d . The flexible portion  209   c  comprises an upper portion  701  and a lower portion  702 , the lower portion  702  comprising an extension  703 . A universal joint spider  604   b  comprises generally cylindrical bearing carriers  605   b  and is disposed such that an axial centerline  606  of the bearing carriers  605   b  intersects a center of curvature of a generally spherical interface  704 . The bearing carriers  605   b  are held in bushings or bearings  607  in the upper portion  701  of the flexible portion  209   c.    
       FIG. 7   b  discloses the same embodiment as  FIG. 7   a , with the drilling assembly  102   d  rotated 90 degrees. The universal joint spider  604   b  comprises generally cylindrical bearing carriers  608 , an axial centerline  609  of which intersects the center of curvature of the generally spherical interface  704 . Bearing carriers  608  extend into bushings or bearings  610  disposed in the extension  703  of the lower portion  702 . The bushings  607  and  610  may be made from any suitable material including bronze, steel, Babbitt metal, or a polymer. 
       FIG. 8   a  discloses an embodiment of an indenting member  107   c . In this embodiment, a polycrystalline diamond compact  801   a  is brazed or otherwise affixed to a distal end  803   b  of a shank  802   a . The polycrystalline diamond compact  801   a  may be disposed coaxial to the shank  802   a , and the polycrystalline diamond compact  801   a  may comprise pointed geometry  805 . The shank  802   a  may be constructed from a steel alloy, and may be case hardened, heat treated, or otherwise processed to improve abrasion resistance. The shank  802   a  may comprise hard-facing. 
       FIG. 8   b  discloses another embodiment of an indenting member  107   d . In this embodiment, a polycrystalline diamond compact  801   b  is brazed or otherwise affixed to a distal end  803   c  of a shank  802   b . An axial centerline of the polycrystalline diamond compact  801   b  and an axial centerline of the shank  802   b  may be offset. 
       FIG. 8   c  discloses another embodiment of an indenting member  107   e . A shank  802   c  comprises a distal end  803   d  which may be cast, machined, forged, or otherwise formed into a generally polygonal shape  820 . The generally polygonal shape  820  may be asymmetric with respect to an axial centerline of the shank  802   c.    
       FIG. 8   d  discloses another embodiment of an indenting member  107   f . In this embodiment, the indenting member  107   f  comprises a shank  802   d  and a distal end  803   e . The distal end  803   e  may comprise generally conical geometry  825 , and may be asymmetric with respect to an axial centerline of the shank  802   d . The distal end  803   e  may comprise hard-facing or other material or treatment intended to reduce abrasive wear. 
       FIG. 9  discloses another embodiment of a drilling assembly  102   e  according to the present invention. Drilling assembly  102   e  comprises a flexible portion  209   d  disposed intermediate, or between, a drill bit  104   f  and a portion of drill string  109   b . The flexible portion  209   d  comprises an interface  901  intermediate, or between, an upper segment  210   b  and a lower segment  211   b . The interface  901  may be protected from abrasion and wear by a bellows-type cover  902 . The cover  902  may be made from electron-beam welded sheet metal or another material. 
     The interface  901  may comprise a seal  903  disposed intermediate the upper segment  210   b  and the lower segment  211   b . The seal  903  may comprise an o-ring or wiper seal, and may be adapted to retain lubrication on the interface  901 . The interface  901  may be sealed from contact with drilling fluid or may be open to the drilling fluid. 
     A shaft  111   b  may be disposed intermediate an indenting member  107   g  and a rotating element  114   c . In this embodiment, the shaft  111   b  comprises two universal joints  904  adapted to allow the shaft  111   b  to deflect according to the deflection of the flexible portion  209   d.    
       FIG. 10   a  discloses another embodiment of a drilling assembly  102   f . In this embodiment, the drilling assembly  102   f  comprises a flexible portion  209   e  and includes a sliding collar  1001  comprising ports  1002 . Fluid passages  1003  are in communication with a plurality of pistons  1004 . The plurality of pistons  1004  are attached to mechanical stops  219   b.    
     Referring now to  FIG. 10   b , the ports  1002  in the sliding collar  1001  are now in communication with a plurality of fluid passages  1003 . Drilling fluid  1005  is diverted into and creates fluid pressure in passages  1003 . 
     Referring now to  FIG. 10   c , which is a detailed view of  FIG. 10   b , drilling fluid  1005  creates fluid pressure in the passages  1003  that forces the plurality of pistons  1004  and mechanical stops  219   b  inward to contact a lower segment  211   c  of the flexible portion  209   e . Flexible portion  209   e  is thus immobilized to allow drilling of straight wellbores. 
       FIG. 11   a  discloses another embodiment of a drilling assembly  102   g . In this embodiment, a lower segment  211   d  of a flexible portion  209   f  comprises a threaded sleeve  1101  engaged with a threaded collar  1102 . The threaded sleeve  1101  is free to rotate on an extension  212   b  of a lower segment  211   d  of the flexible portion  209   f . An electric motor  1103  rotates the threaded sleeve  1101 , and alignment pins  1104  prevent the rotation of the threaded collar  1102 . As the electric motor  1103  rotates the threaded sleeve  1101 , the non-rotating threaded collar  1102  moves upward. Maximum angular deflection of the flexible portion  209   f  can be controlled by adjusting the position of the threaded collar  1102 , and as the threaded collar  1102  moves upward it aligns the flexible portion  209   f  to a position of zero angular deflection. 
     Referring now to  FIG. 11   b , the threaded collar  1102  is engaged with the rotatable threaded sleeve  1101 . The threaded collar  1102  is in its maximum upward position, effectively immobilizing the flexible portion  209   f  to allow for straight drilling. 
       FIG. 12  discloses another embodiment of a drilling assembly  102   h . In this embodiment, a collar  1201  comprises a distal end  1202  with a generally conical geometry  1203 . A flexible portion  209   g  comprises a lower segment  211   e  with an extension  212   c , which also comprises generally conical geometry  1204 . The collar  1201  may be movable in a direction coaxial with an axial centerline  1205   a  of the drilling assembly  102   h . The position of the collar  1201  determines the maximum angular deflection of the lower portion  211   e  of the flexible portion  209   g . The position of the collar  1201  may be controlled by a mechanical, electronic, hydraulic, or other system, or combinations thereof. As the collar  1201  moves toward the lower portion  211   e  of the flexible portion  209   g , the generally conical geometries  1203  and  1204  are brought into mechanical contact and the lower portion of the joint  211   e  self-aligns with the collar  1201  and the flexible portion  209   g  reaches a position of zero angular deflection. 
       FIG. 13  discloses another embodiment of a drilling assembly  102   i . A drill bit  104   g  comprises a plurality of grooves  1301  intermediate, or between, a working face  106   e  and a shank  108   e . The grooves  1301  may be circumferential, helical, or otherwise oriented and may be machined, forged, cast, or otherwise formed in the drill bit  104   g . The grooves  1301  allow for elastic, angular deflections in the drill bit  104   g.    
       FIG. 14  discloses another embodiment of a drilling assembly  102   j . A flexible portion  209   h  is disposed intermediate, or between, a drill bit  104   h  and a portion of a drill string  109   c . The flexible portion  209   h  comprises a compliant segment  1401  and an outer sleeve  1402 . A collar  1403  is moveable in a direction coaxial to an axial centerline  1205   b  of the drilling assembly  102   j . Mechanical stops  1404  are disposed internal to the outer sleeve  1402 . The collar  1403  may selectively be brought into mechanical contact with the stops  1401 , thus limiting or disallowing angular deflection of the compliant segment  1401  and the drill bit  104   h.    
       FIG. 15  is a diagram of a method  2900  for steering a downhole tool string. The method comprises the steps of providing  2901   a  drill bit assembly attached to an end of the tool string disposed within a bore hole; providing  2902  a shaft protruding from a working portion of the drill bit assembly, the working portion comprising at least one cutting element; engaging  2903  the formation with a distal end of the shaft, the shaft being part of the drill bit assembly; and angling  2904  the drill bit assembly with the shaft along a desired trajectory. The step of angling  2904  the drill bit assembly with the shaft may comprise angling the shaft or the step may include pushing the drill bit assembly along the desired trajectory with the shaft. It is believed that if the shaft is loaded with enough pressure that the shaft will penetrate the formation, but if the shaft does not overcome the formation pressure, then the shaft may move the drill bit assembly by pushing off of the formation. A narrow distal end may aid in concentrating the pressure loaded to the shaft into the formation such that it may overcome the formation pressure and penetrate the formation; on the other hand, a blunt or wide distal end may prevent the shaft from penetrating the formation and allow the shaft to push off of the formation. In some embodiments, the shaft may advance along the desired trajectory before the drill bit assembly. The shaft may be at least partially disposed within a chamber generally coaxial with the shank portion of the assembly and the chamber may be disposed within a body portion of the assembly. Angling  2904  the drill bit assembly may be controlled over a downhole network. 
     In some embodiments, the shaft is rotationally isolated from the working portion of the drill bit assembly. This may be advantageous because it allows the shaft to remain on the desired trajectory even though the remainder of the drill bit assembly is rotating. In some embodiments of the method, the shaft may also rotate with the body portion of the drill bit assembly if there is a plurality of actuators timed to temporally move the shaft such that the distal end of the shaft stays on the desired trajectory. 
     Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.