Patent Publication Number: US-11643883-B1

Title: Adjustable flex system for directional drilling

Description:
BACKGROUND 
     Generally, wellbores are drilled through hydrocarbon-bearing subsurface formations to obtain hydrocarbons such as oil and gas. Some wellbores include vertical portions, as well as horizontal/lateral portions. Indeed, a wellbore may extend vertically downward from a surface of the drilling operation and transition, via a curved portion (e.g., dogleg portion), to a horizontal portion at a desired depth in the subsurface formation. During drilling operations, a rotary steerable system tool may be implemented in a downhole drilling operation to guide a drilling path of the bottom hole assembly (BHA). The rotary steerable system may veer the BHA from a vertical drilling path to a horizontal drilling path. For some subsurface formations, a curved portion having a high dogleg severity may be desirable. As such, some rotary steerable systems may include a flexible tool such that the rotary steerable system may increase a dogleg severity (i.e., a measure of the change in direction of a wellbore over a defined length) of the curved portion of the wellbore. 
     Unfortunately, the flexible tool may hinder drilling operations in straight portions of the wellbore (e.g., the vertical portion and/or horizontal portion). In particular, the flexible tool may have decreased torsional stiffness making the BHA less suitable for steering controllability and vibration mitigation, which may lead to an increased risk of stick-slip, whirl, and/or other issues. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These drawings illustrate certain aspects of some of the embodiments of the present disclosure and should not be used to limit or define the method. 
         FIG.  1    illustrates a downhole drilling system, in accordance with some embodiments of the present disclosure. 
         FIGS.  2 A- 2 D  illustrate cross-sectional views of an adjustably flexible downhole tool having an annular piston, in accordance with some embodiments of the present disclosure. 
         FIG.  3 A- 3 C  illustrate a cross-sectional views of an adjustably flexible downhole tool having an annular piston and a pivot guide, in accordance with some embodiments of the present disclosure. 
         FIGS.  4 A &amp;  4 B  illustrate cross-sectional views of an adjustably flexible downhole tool having a plurality of rings, in accordance with some embodiments of the present disclosure. 
         FIGS.  5 A &amp;  5 B  illustrate cross-sectional views of an adjustably flexible downhole tool having an actuating sleeve disposed in a first position and a second position, respectively, in accordance with some embodiments of the present disclosure. 
         FIG.  6    illustrates a cross-sectional view of an adjustably flexible downhole tool having a mechanical actuator configured to drive the sleeve from the first position to the second position, in accordance with some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed herein are systems and methods for an adjustably flexible downhole tool. In particular, a bottom hole assembly comprises the adjustably flexible downhole tool, as well as a rotary steerable system for steering the bottom hole assembly (BHA) assembly during drilling operations. As set forth in detail below, the adjustably flexible downhole tool may have at least one adjustable member configured to adjust a stiffness of the adjustably flexible downhole tool as the BHA moves along the wellbore. For example, the adjustably flexible downhole tool may be adjusted to be more flexible for curved portions (e.g., dogleg portions) such that the rotary steerable system may increase a dogleg severity (i.e., a measure of the change in direction of a wellbore over a defined length) of the curved portion of the wellbore. Further, the adjustably flexible downhole tool may be adjusted to be stiffer along straight portions of the wellbore for improved steering controllability, vibration mitigation, and/or other benefits. 
       FIG.  1    illustrates a downhole drilling system  100 , in accordance with some embodiments of the present disclosure. As illustrated, a drilling platform  110  may support a derrick  112  having a traveling block  114  for raising and lowering drill string  116 . The drill string  116  may comprise, but is not limited to, drill pipe and coiled tubing, as generally known to those skilled in the art. A kelly  118  may support drill string  116  as it may be lowered through a rotary table  120 . A top drive system may be used in place of a kelly. A bottom hole assembly  134  having a drill bit  122  may be attached to the distal end of the drill string  116  and may be driven either by a downhole motor and/or via rotation of the drill string  116  from surface  108 . Without limitation, the drill bit  122  may comprise, roller cone bits, polycrystalline diamond compact (PDC) bits, natural diamond bits, any hole openers, reamers, coring bits, and the like. As the drill bit  122  rotates, it may form a wellbore  102  along a drilling path of the drill bit  122 . The wellbore  102  may extend from a wellhead  104  into a subterranean formation  106  from the surface  108 . As illustrated, the wellbore  102  may comprise a vertical portion  154 , a curved portion  156 , and a horizontal portion  158 . However, in some embodiments, the wellbore  102  may comprise portions with other orientations (e.g., a slanted portion). 
     A rotary steerable system  130  of the bottom hole assembly  134  may be configured to steer the drill bit  122  through the subterranean formation  106  to form the various portions of the wellbore  102 . The bottom hole assembly  134  may further comprise an adjustably flexible downhole tool  150  configured to support the rotary steerable system  130  in steering the drill bit  122 . For example, the adjustably flexible downhole tool  150  may be adjusted to be more flexible while drilling the curved portion(s)  156  and may be adjusted to be stiffer while drilling straight portions (e.g., the vertical portion  154 , the horizontal portion  158 , etc.). Moreover, the rotary steerable system  130  may comprise any number of tools, such as sensors  136 , transmitters, and/or receivers to perform downhole measurement operations or to perform real-time health assessment of a rotary steerable system  130  during drilling operations. Further, the rotary steerable system  130  may comprise any number of different measurement assemblies, communication assemblies, battery assemblies, and/or the like. Moreover, the sensors  136  may be connected to information handling system  138 . There may be any number of sensors  136  disposed in the BHA  134  or rotary steerable system  130 . 
     Moreover, the rotary steerable system  130  may be connected to and/or controlled by information handling system  138 , which may be disposed on surface  108  or downhole in the rotary steerable system  130 . A communication link  140  may provide transmission of measurements from the sensors  136  to the information handling system  138 , as well as commands from the information handling system  138  to the rotary steerable system  130 . The communication link  140  may include, but is not limited to, wired pipe telemetry, mud-pulse telemetry, acoustic telemetry, and electromagnetic telemetry. Further, the information handling system  138  may comprise a personal computer  141 , a video display  142 , a keyboard  144  or any suitable input device, and/or non-transitory computer-readable media  146  (e.g., optical disks, magnetic disks) that can store code representative of the methods described herein. 
       FIGS.  2 A- 2 D  illustrate cross-sectional views of an adjustably flexible downhole tool having an annular piston, in accordance with some embodiments of the present disclosure. In particular,  FIG.  2 A  illustrates the annular piston disposed in the first position and  FIG.  2 B  illustrates the annular piston disposed in the second position. With regard to  FIG.  2 A , the adjustably flexible downhole tool  150  may comprise a shaft  202  extending between a first connector end  204  and a second connector end  206 . The shaft  202  may be rigidly secured to the first connector end  204  and the second connector end  206  via a unibody construction, a threaded connection, and/or at least one fastener. Further, the shaft  202  may have a substantially cylindrical shape with a central bore  208  extending through the shaft  202  along a central axis of the shaft. However, in some embodiments, the central bore  208  may also be offset eccentrically from the central axis of the shaft. During drilling operations, the central bore  208  may provide a fluid passageway for drilling fluid to pass through the adjustably flexible downhole tool  150  to other portions of the BHA  134  disposed downhole of the adjustably flexible downhole tool  150 . Moreover, the shaft  202  may comprise one or more secondary bores  222  extending through the shaft  202  and configured to house wiring and/or other communication mediums. 
     The adjustably flexible downhole tool  150  may also comprise an outer sleeve  210  disposed around at least a portion of the length of shaft  202 . The outer sleeve  210  may be annular such that the outer sleeve radially encloses the shaft  202 . In some embodiments, the outer sleeve  210  may comprise radial slots, gaps, or other spaces such that the outer sleeve  210  only partially encloses the shaft  202 . Moreover, as illustrated, an anchored end  224  of the outer sleeve  210  may be connected to the first connector end  204 , and the outer sleeve  210  may extend axially from the first connector end  204  in a direction toward the second connector end  206 . A free end  226  of the outer sleeve  210 , opposite the anchored end  224 , may be disposed proximate the second connector end  206 . In the illustrated embodiment, the free end  226  is not attached to the second connector end  206 . That is, the outer sleeve  210  may be cantilevered from the first connector end  204 . Moreover, the outer sleeve  210  may be secured to the first connector end  204  via a threaded connection, welding, fasteners (e.g., screws, pins, etc.), and/or press-fitting a radially inner sleeve surface  212  of the outer sleeve against a radially outer connector surface  230  of the first connector end  204 . 
     The radially inner sleeve surface  212  of the outer sleeve  210  may be radially offset from a radially outer shaft surface  236  of the shaft  202  such that an annulus  220  is formed between the outer sleeve  210  and the shaft  202 . At least one adjustable member  240  may be disposed in the annulus  220  defined between the shaft  202  and the outer sleeve  210 . As illustrated, the at least one adjustable member  240  comprises an annular piston  214  configured to move axially with respect to outer sleeve  210  and shaft  202 . In the illustrated embodiment, the annular piston  214  is disposed in a first position located proximate the first connector end  204 . However, the annular piston  214  may be configured to move axially along the shaft  202  from the first position to the second position located proximate the free end  226  of the outer sleeve and/or the second connector end  206 . Moving the annular piston  214  from the first position toward the second position may increase bending stiffness and/or torsional stiffness of the adjustably flexible downhole tool. 
     A radially inner piston surface  270  of the annular piston  214  may be configured to interface with the radially outer shaft surface  236  of the shaft  202 , and a radially outer piston surface  272  of the annular piston may be configured to interface with the radially inner sleeve surface  212  of the outer sleeve  210 . As such, the annular piston  214  may at least partially restrain radial movement (e.g., deflection/bending) of the shaft  202  with respect to the outer sleeve  210  at a location of the annular piston  214 . During drilling operations, the adjustably flexible downhole tool  150  may experience forces in certain locations along the wellbore (e.g., the curved portion  156 ) that cause the adjustably flexible downhole tool  150  to bend. In particular, as the shaft  202  is connected at both ends (e.g., to the first connector end  204  and the second connector end  206 ), the shaft  202  may bend due to the forces present along the curved portion  156 . Generally, as the outer sleeve  210  is cantilevered from the first connector end  204 , the outer sleeve may not support the shaft  202 . However, as the annular piston  214  is configured to interface with both the shaft  202  and the outer sleeve  210 , the outer sleeve  210  may support the shaft  202  (e.g., to restrain bending) at the location of the annular piston  214 . 
     In the illustrated embodiment, the annular piston  214  is disposed in the first position. As the first position is disposed proximate the first connector end  204 , only a portion of the outer sleeve  210  (e.g., between the first connector end  204  and the annular piston  214 ) is configured to help restrain radial movement (e.g., bending) of the shaft  202 . However, as the annular piston  214  moves toward the second connector end  206 , more of the length of the outer sleeve  210  may be configured to support more of the length of the shaft  202 , which is configured to increase the bending stiffness of the adjustably flexible downhole tool  150 . As such, the adjustably flexible downhole tool  150  may be adjusted between a flexible state (e.g., with the annular piston  214  in the first position) and a stiffer state (e.g., with the annular piston  214  in the second position). In some embodiments, the stiffness of the adjustably flexible downhole tool  150  may be variable adjusted. That is, the annular piston  214  may be positioned at any axial position along the shaft  202  between the first position and the second position to provide additional stiffness control for the adjustably flexible downhole tool  150 . For example, the adjustably flexible downhole tool  150  may move through a curved portion  156  of the wellbore  102  that has a low dogleg severity. To maintain higher steering controllability and/or vibration mitigation while still increasing the flexibility of the adjustably flexible downhole tool  150  to reduce strain, the annular piston  214  may be moved to a position disposed between the first position and the second position. 
     An actuator  218  may be configured to drive the adjustable member  240  (e.g., annular piston  214 ) along the shaft  202  between the first position and the second position. In some embodiments, the actuator  218  may be configured to provide unidirectional movement of the annular piston  214  (e.g., in a direction from the first connector end  204  toward the second connector end  206 ). However, in some embodiments, the actuator  218  may be configured to provide bidirectional movement of the annular piston  214  along the shaft  202 . Further, the actuator  218  may be configured to drive the adjustable member  240  on demand. That is, the actuator  218  may be configured to receive signal, via electrical communication, fluid communication, or any other suitable communication mechanism, and drive the adjustable member  240  in response to receiving the signal. In the illustrated embodiment, the actuator  218  comprises a hydraulic system  238  having at least a control valve  242  and a fluid passageway  244  extending from the central bore  208  to a sealed chamber  246 . The sealed chamber  246  may be defined by a portion of the annulus  220  between the first connector end  204  and the annular piston  214 . In some embodiments, to help isolate the sealed chamber  246  from the downhole environment, the annular piston  214  may comprise a plurality of seals to form a seal between the annular piston  214  and the shaft  202 , as well as between the annular piston  214  and the outer sleeve  210 . 
     Moreover, to move the annular piston  214  in the direction from the first position toward the second position, the control valve  242  may be configured to open the fluid passageway  244  in response to a control signal; thereby, permitting fluid from the central bore  208  to pass through the fluid passageway  244  and enter the sealed chamber  246 . As the fluid enters the sealed chamber  246 , the pressure in the sealed chamber  246  may increase. In response to the pressure in the sealed chamber  246  exceeding a threshold pressure, the annular piston  214  may move in the direction toward the second connector end  206 . Further, the actuator  218  may comprise an electrical motor, or any other suitable actuator or combination of actuators, to move the annular piston  214  between the first position and the second position. 
     Further, the adjustably flexible downhole tool  150  may also comprise a debris barrier  232  configured to prevent downhole debris from moving into the annulus  220 . For example, the debris barrier  232  may comprise a screen to filter out debris moving into the annulus  220 . The debris barrier  232  may be secured in the annulus  220  in a location proximate the second connector end  206 . In particular, the debris barrier  232  may be disposed between the second position of the annular piston  214  and the second connector end  206  such that the debris barrier  232  does not inhibit movement of the annular piston  214  along the annulus  220  between the first position and the second position. Moreover, the debris barrier  232  may span between the shaft  202  and the outer sleeve  210 . 
     With regard to  FIG.  2 B , the adjustably flexible downhole tool  150  comprises the annular piston  214  disposed in the second position. As set forth above, the actuator  218  may be configured to move the annular piston  214  axially along the shaft  202  between the first position (shown in  FIG.  2 A ) and the second position. In some embodiments, the adjustably flexible downhole tool  150  may comprise a stop mechanism  280  configured to restrain axial movement of the annular piston  214  at the second position in at least the direction toward the second connector end  206 . For example, the stop mechanism  280  may comprise an annular stop ring  248  rigidly secured to the radially outer shaft surface  236  and/or the radially inner sleeve surface  212  in a position proximate the second position such that the annular stop ring  248  may contact the annular piston  214  to stop movement of the annular piston  214  at the second position. In the illustrated embodiment, the annular stop ring  248  is rigidly secured to the radially inner sleeve surface  212  proximate the second position of the annular piston  214 . 
     Alternatively, the stop mechanism  280  may comprise a wedge disposed proximate the second position. For example, the shaft  202  may comprise a wedge protruding into the annulus  220  from the radially outer shaft surface  236 . Alternatively, the diameter of the shaft  202  may gradually increase along the length of the shaft  202  in the direction toward the second connector end  206 , starting from the second position, to form the wedge (e.g., tapered surface). The wedge may be configured to restrain axial movement of the annular piston  214  in the direction toward the second connector end  206  and/or secure the annular piston  214  at the second position. Likewise, the outer sleeve  210  may comprise a wedge (e.g., tapered surface) protruding into the annulus  220  from the radially inner sleeve surface  212 . In addition, the annular piston  214  may have a tapered portion. In particular, the radially inner piston surface  270  and/or radially outer piston surface  272  may comprise tapered portions. As the annular piston  214  moves into the second position, the tapered portion of radially inner piston surface  270  may engage the wedge of shaft  202  and the tapered portion of radially outer piston surface  272  may engage the wedge of outer sleeve  210 . The engagement of both tapered portions may create a more rigid coupling of shaft  202  to outer sleeve  210  through annular piston  214  at the second position. Indeed, removing the radial clearance between shaft  202 , annular piston  214 , and outer sleeve  210  may make the adjustably flexible downhole tool  150  more laterally stiff and less prone to wear from relative movement of parts in abrasive drilling mud during drilling operations. Further, the rigid coupling of shaft  202  to outer sleeve  210  through annular piston  214  at the second position may increase the torsional stiffness of the adjustably flexible downhole tool  150 . 
     With regard to  FIG.  2 C , the adjustably flexible downhole tool  150  may further comprise a torsional stiffener mechanism  284  configured to increase the torsional stiffness of the adjustably flexible downhole tool  150  as the annular piston  214  moves toward the second position. The torsional stiffener mechanism  284  may be configured to restrain rotational movement of the annular piston  214  with respect to the shaft  202 , as well as rotational movement of the annular piston  214  with respect to the outer sleeve  210 , at the location of the annular piston  214 . In some embodiments, the torsional stiffener mechanism may comprise a track  228  configured to restrain rotational movement of the annular piston  214  with respect to the shaft  202  and the outer sleeve  210  while still permitting axial movement of the annular piston  214  between the first position and the second position. The track  228  may comprise a slot and key configuration. For example, the annular piston  214  may comprise a first key  286  (e.g., protrusion) extending from the radially inner piston surface  254  and a second key  288  (e.g., protrusion) extending from the radially outer piston surface  258 . Further, the shaft  202  may comprise a first slot  290 , corresponding to the first key  286 , that extends axially from at least the first position to the second position, and the outer sleeve  210  may comprise a second slot  292 , corresponding to the second key  288 , that extends axially from at least the first position to the second position. The annular piston  214  may be configured to move axially along the shaft  202  with the first key  286  disposed in the first slot  290  and the second key  288  disposed in the second slot  292  such that the respective key and slot interfaces restrain rotational movement of the annular piston  214  with respect to the shaft  202  and the outer sleeve  210 . In some embodiments, shaft  202  and/or the outer sleeve  210  may comprise additional keys and/or slots may be added. 
       FIG.  2 D  illustrates another embodiment of the adjustably flexible downhole tool  150  having a torsional stiffener mechanism  284  configured to increase the torsional stiffness of the adjustably flexible downhole tool  150 . The torsional stiffener mechanism  284  may comprise splined surfaces (e.g., a first splined surface  294  and a second splined surface  296 ) on the shaft  202  and/or the outer sleeve  210 , respectively, that are configured to interface with corresponding splined surfaces (e.g., a radially inner splined surface  298  and a radially outer splined surface  201 ) on the annular piston  214 . The splined surfaces may restrain rotational movement of the annular piston  214  with respect to the shaft  202  and the outer sleeve  210  while still permitting axial movement of the annular piston  214 . In the illustrated embodiment, each of the shaft  202 , the outer sleeve  210 , and the annular piston  214  comprise respective splined surfaces. Moreover, as illustrated, the splined surfaces may extend about the circumference of the respective shaft  202 , outer sleeve  210 , and/or annular piston  214 . However, in some embodiments, the splined surfaces may only extend about a portion of the circumference of the respective shaft  202 , outer sleeve  210 , and/or annular piston  214 . 
       FIGS.  3 A- 3 C  illustrate a cross-sectional views of an adjustably flexible downhole tool  150  having an annular piston  214  and a pivot guide  300 , in accordance with some embodiments of the present disclosure. As shown in  FIG.  3 A , the pivot guide  300  may be disposed within the annulus  220  formed between the shaft  202  and the outer sleeve  210  in a location proximate to second connector end  206 . The pivot guide  300  may provide radial support between shaft  202  and outer sleeve  210 , proximate the second connector end  206 , to hold the outer sleeve  210  substantially concentric with the shaft  202  at the location of the pivot guide  300 . However, the pivot guide  300  is configured to permit the shaft  202  to bend (e.g., deflect) within the outer sleeve  210  when the adjustable member (e.g., annular piston  214 ) is in a first position. Indeed, the pivot guide  300  may comprise of a spherical bearing  302  that is allowed to pivot such that the shaft  202  may deflect radially with respect to outer sleeve  210  between annular piston  214  and pivot guide  300 . In some embodiments, the pivot guide  300  may comprise a coupling  304  that is configured to pivot to allow radial deflection of shaft  202 , but restrains rotational movement between the shaft  202 , the pivot guide  300 , and the outer sleeve  210  (e.g., torsional coupling). Torsional coupling between the shaft  202 , the pivot guide  300 , and the outer sleeve  210  may be achieved via threads, splines, or keys, such that the coupling  304  may pivot to allow shaft  202  to deflect radially with respect to outer sleeve  210  between annular piston  214  and pivot guide  300 . The coupling  304  may comprise a crowned spline or a constant velocity (CV) joint such as is used in mud motor transmissions. With the torsional coupling, adjustably flexible downhole tool  150  may be configured to achieve a higher torsional stiffness than the shaft  202  alone, while still achieving a variable radial stiffness. 
     Moreover, the annular piston  214  may be moved on demand, in a direction toward the pivot guide  300 , to adjust the adjustably flexible downhole tool  150  to be more radially stiff. Indeed, a variable radial stiffness may be achieved based at least in part on the position of annular piston  214  between first position and pivot guide  300 . The adjustably flexible downhole tool  150  may be most stiff position with the annular piston  214  disposed directly adjacent pivot guide  300 . 
       FIG.  3 B  illustrates an embodiment of the adjustably flexible downhole tool  150  having a pivot guide  300 . In the illustrated embodiment, the pivot guide  300  comprises splined pivot surfaces (e.g., a first splined pivot  306  surface and a second splined pivot surface  308 ). The first splined pivot surface  306  may be formed in the radially outer shaft surface  236  of the shaft  202 . Further, the second splined pivot surface  308  may be formed on the radially inner sleeve surface  212  of the outer sleeve  210 . During operation, the first splined pivot surface  306  is configured to interface with the second splined pivot surface  308  to restrain rotational movement of the shaft  202  with respect to the outer sleeve  210 ; thereby, increasing torsional stiffness of the adjustably flexible downhole tool  150 . Further, as set forth above, the pivot guide  300  (e.g., the splined pivot surfaces  306 ,  308 ) are also configured to provide radial support between shaft  202  and outer sleeve  210 , proximate the second connector end  206 , to hold the outer sleeve  210  substantially concentric with the shaft  202  at the location of the pivot guide  300  while still permitting the shaft  202  to bend (e.g., deflect) within the outer sleeve  210 . Moreover, the splined pivot surfaces  306 ,  308  may comprise a crowned splines, parallel splines, serrated splines, etc.). 
       FIG.  3 C  illustrates an embodiment of the first splined pivot surface  306  of the shaft  202  of the adjustably flexible downhole tool  150 . In the illustrated embodiment, the first splined pivot surface  306  comprises a crowned spline  310  having a plurality of teeth  312  and a base surface  314 . The plurality of teeth  312  protrude radially outward from the base surface  314 . Further, an outer tooth surface  316  of each tooth of the plurality of teeth  312  may be curved or rounded along the axial length of the first splined pivot surface  306 . In particular, the outer tooth surface  316  of each tooth may be radiused. Further, the base surface  314  may be curved or rounded along the axial length of the first splined pivot surface  306  such that the shaft  202  may roll or pivot with respect to the outer sleeve  210  at the first splined pivot surface  306 . As such, the base surface  314  may be radiused. 
       FIGS.  4 A &amp;  4 B  illustrate cross-sectional views of an adjustably flexible downhole tool having a plurality of rings, in accordance with some embodiments of the present disclosure. Referring to  FIG.  4 A , the adjustably flexible downhole tool  150  comprises the shaft  202  extending between the first connector end  204  and the second connector end  206 . Further, the adjustably flexible downhole tool  150  may comprise the at least one adjustable member  240 . In the illustrated embodiment, the at least one adjustable member  240  comprises a plurality of annular rings  402  disposed about the radially outer shaft surface  236  of the shaft  202  and along a length of the shaft  202 . Each annular ring of the plurality of annular rings  402  is configured to move axially, with respect to the shaft  202 , from a respective first position to a respective second position. Moving the plurality of annular rings  402  to the second position may increase bending stiffness and/or torsional stiffness of the adjustably flexible downhole tool  150 . 
     In the illustrated embodiment, each ring of the plurality of annular rings  402  is disposed in a first position such that the adjustably flexible downhole tool  150  is in a flexible configuration. In the first position, each annular ring  402  may be spaced apart from adjacent annular rings  402 . Indeed, there may be sufficient axial and/or radial clearance between respective interlocking features of adjacent annular rings of the plurality of annular rings  402  that each annular ring may move radially and/or axially with respect to respective adjacent annular rings. As each annular ring may move freely with respect to adjacent annular rings, the plurality of annular rings  402  may not restrain bending of the shaft  202  such that the adjustably flexible downhole tool  150  may be in the flexible configuration. 
     Referring to  FIG.  4 B , the plurality of annular rings  402  are disposed in a second position. As set forth above, each annular ring of the plurality of annular rings  402  is configured to move axially, with respect to the shaft  202 , from the respective first position to the respective second position. At the second position, each ring of the plurality of annular rings  402  may axially and/or radially interface with at least one adjacent annular ring to restrain radial movement of the shaft  202  and increase bending stiffness and/or torsional stiffness of the adjustably flexible downhole tool  150 . In the illustrated embodiment, each annular ring of the plurality of annular rings  402  comprises a first interlocking feature  404  at a first axial end  406  of the annular ring  402  and a second interlocking feature  408  at a second axial end  410  of the annular ring  402 . As illustrated, the first interlocking feature  404  may comprise a protrusion  412  and the second interlocking feature  408  may comprise a recess  414 . The protrusion  412  may comprise a chevron shape. That is, the protrusion  412  may be tapered from both the radially outer ring surface  416  and the radially inner ring surface  418  of the first axial end  406  toward a tip  420  of the protrusion  412 . The recess  414  may be defined by a corresponding chevron shape. As such that the protrusion  412  of a first annular ring  422  may be inserted into a corresponding recess  414  of an adjacent annular ring (e.g., a second annular ring  424 ) with the annular rings in the second position. In the second position, the second interlocking feature  408  (e.g., the recess  414 ) of the second annular ring  424  may interface with the first interlocking feature  404  (e.g., the protrusion  412 ) of the first annular ring  422  to restrain axial and radial movement of the first and second annular rings with respect to each other. Indeed, with the interlocking features interfaced, the plurality of annular rings may operate as a stiff annular sleeve configured to support the shaft  202 , which may increase bending stiffness and/or torsional stiffness of the adjustably flexible downhole tool  150 . 
     As set forth above, the adjustably flexible downhole tool  150  may comprise the actuator  218 . The actuator  218  may be configured to drive each annular ring of the plurality of annular rings  402  axially to move from the respective first positions to the respective second positions. In some embodiments, the actuator  218  may comprise a push ring  426  and an electric motor configured to drive the push ring  426  in an axial direction toward the plurality of annular rings  402 . The push ring  426  may be disposed about the shaft  202  at an end of the plurality of annular rings  402 . In some embodiments, the push ring  426  is threaded to the shaft  202 , the first connector end  204 , or the second connector end  206  such that driving the push ring  426  in an axial direction comprises rotating/threading the push ring  426 . Indeed, the push ring  426  may move axially as it rotates to produce an axial force on the plurality of annular rings  402 . The axial force may drive the plurality of annular rings  402  from the respective first positions to the respective second positions. For example, the push ring  426  may be threaded to the second connector end  206  such that the actuator  218  may driving the push ring  426  in a direction toward the first connector end  204 . As such, the push ring  426  may drive the plurality of annular rings  402  in a direction toward the first connector end  204  and compress the annular rings  402  against a shoulder  428  of the first connector end  204  and/or a ring adapter  440  disposed between the shoulder  428  and the annular rings  402 . Compressing the plurality of annular rings against the first connector end  204  (e.g., moving each of the annular rings  402  from the respective first position to the respective second position) may reduce or remove axial and/or radial clearance between each of the plurality of annular rings  402 ; thereby, interfacing adjacent interlocking features  404 ,  408  of the plurality of annular rings  402 . Compressing the plurality of annular rings  402  may not require a large amount of axial force. 
     Moreover, the adjustably flexible downhole tool  150  may comprise a locking feature  430  configured to axially hold the plurality of annular rings  402  in the second position. The locking feature  430  may comprise threading, an expandable locking ring, a collet, a spring energized lock, or any combination thereof. For example, the push ring  426  may be configured to interface with an exterior annular ring  432  of the plurality of annular rings  402  to drive the plurality of annular rings  402  to the second position. The exterior annular ring  432  may comprise a ring slot  434  configured to house an expandable locking ring  438 . Further, the shaft  202  may comprise shaft slot  436  disposed in a location corresponding to the second position of the exterior annular ring  432 . As the exterior annular ring  432  moves into the second position, the expandable locking ring  438  may expand into the shaft slot  436  and lock the exterior annular ring  432  in the second position. Locking the exterior annular ring  432  in the second position may axially hold the plurality of annular rings  402  in the second position. 
     Additionally, the adjustably flexible downhole tool  150  may comprise a torsional locking feature to increase torsional stiffness of the adjustably flexible downhole tool  150 . The torsional locking feature may restrain rotational movement of the plurality of annular rings  402  with respect to the shaft  202 . In some embodiments, the torsional locking feature may comprise a key and slot configuration (shown in  FIG.  2 C ). For example, the shaft  202  may comprise a slot in the radially outer shaft surface  236  that extends along at least a portion of the length of the shaft  202 . Further, each annular ring of the plurality of annular rings  402  may comprise a key (e.g., protrusion), corresponding to the slot. The plurality of annular rings  402  may be configured to move axially along the shaft  202  with the key disposed in the respective slots. However, the interface between the key and respective slots may restrain rotational movement of the annular rings  402  with respect to the shaft  202 , which may increase the torsional stiffness of the adjustably flexible downhole tool  150 . Further, the torsional locking feature may be configured to restrain rotational movement of the plurality of annular rings  402  with respect to each other. In some embodiments, each annular ring  402  may comprise keys, teeth, enhanced frictional surfaces/materials, or other suitable features configured to interface with adjacent annular rings to restrain rotational movement of the plurality of annular rings  402  with respect to each other. 
       FIGS.  5 A &amp;  5 B  illustrate cross-sectional views of an adjustably flexible downhole tool having an actuating sleeve disposed in a first position and a second position, respectively, in accordance with some embodiments of the present disclosure. Referring to  FIG.  5 A , the adjustably flexible downhole tool  150  comprises the shaft  202  extending between the first connector end  204  and the second connector end  206 . Further, the adjustably flexible downhole tool  150  comprises the outer sleeve  210  disposed around at least a portion of the length of shaft  202 . The outer sleeve  210  may be annular such that the outer sleeve radially encloses the shaft  202 . Further, the annulus  220  may be formed between the shaft  202  and the outer sleeve  210 . That is, the outer sleeve  210  may be radially offset from the shaft  202  such that the shaft  202  may bend (e.g., radially deflect) without contacting the radially inner sleeve surface  212  of the outer sleeve  210 . Moreover, as illustrated, the anchored end  224  of the outer sleeve  210  may be connected to the first connector end  204 , and the outer sleeve  210  may extend axially from the first connector end  204  in a direction toward the second connector end  206 . The free end  226  of the outer sleeve  210 , opposite the anchored end  224 , may be positioned proximate the second connector end  206 . However, as illustrated, the free end  226  is not attached to the second connector end. As such, that the outer sleeve  210  may be cantilevered from the first connector end  204  with the actuating sleeve  500  disposed in the first position. As set forth above, the outer sleeve  210  may be secured to the first connector end  204  via a threaded connection, welding, fasteners (e.g., screws, pins, etc.), and/or press-fitting a radially inner sleeve surface  212  of the outer sleeve  210  against the radially outer connector surface  230  of the first connector end  204 . 
     Further, the adjustably flexible downhole tool  150  may comprise the at least one adjustable member  240 . In the illustrated embodiment, the at least one adjustable member  240  comprises the actuating sleeve  500 . The actuating sleeve  500  may be coupled to the second connector end  206 . Further, the actuating sleeve  500  may be configured to move axially, with respect to the shaft  202 , from the first position to the second position to increase bending stiffness and/or torsional stiffness of the adjustably flexible downhole tool  150 . As illustrated, in the first position, the actuating sleeve  500  is axially offset from the outer sleeve  210  such that the outer sleeve  210  may not support the shaft  202  in the first position. Therefore, adjustably flexible downhole tool  150  may be in a flexible configured with the actuating sleeve  500  in the first position, such that the rotary steerable system  130  may bend sufficiently to achieve a high dog leg severity through curved portions  156  of the wellbore  102 . However, in the second position (shown in  FIG.  5 B ), the actuating sleeve  500  is configured to interface with the outer sleeve  210  to restrain radial movement (e.g., bending) of the shaft  202  with respect to the outer sleeve  210 . 
     Moreover, the adjustably flexible downhole tool  150  may comprise the actuator  218  to drive the actuating sleeve  500  from the first position to the second position. The actuator  218  may comprise a hydraulic actuator, an electric motor, or some combination thereof. In the illustrated embodiment, the actuator  218  comprises a hydraulic system  238  having an electric motor  502  configured to actuate a piston valve  504  to open a fluid line  506  from the central bore  208  to a sealed chamber  508 . The sealed chamber  508  may be defined by a radially inner actuating surface  510  of the actuating sleeve  500  and a second radially outer connector surface  540  of the second connector end  206 . Further, opening the fluid line  506  may permit fluid passing through the central bore  208  to flow into the sealed chamber  508 , which may increase the pressure in the sealed chamber  508 . In some embodiments, a shear pin  526  may be configured to hold the actuating sleeve  500  in the first position. The shear pin  526  may be configured to shear in response to a threshold axial force (e.g., an actuation force) applied to the actuating sleeve  500  such that the actuating sleeve  500  may move from the first position towards the second position to interface with the outer sleeve  210 . Once the piston valve  504  opens the fluid line  506 , the pressure in the sealed chamber  508  may increase sufficiently to apply the threshold axial force to the actuating sleeve  500  such that the actuating sleeve  500  may move from the first position to the second position. 
     Referring to  FIG.  5 B , the actuating sleeve  500  is disposed in the second position. In the second position, the actuating sleeve  500  is interfaced with the outer sleeve  210  to restrain radial movement (e.g., bending) of the shaft  202 . Interfacing the actuating sleeve  500  with the outer sleeve  210  may rigidly connect the outer sleeve  210  with the second connector end  206  such that the outer sleeve  210  is supported at both the anchored end  224  (shown in  FIG.  5 A ) and the free end  226 . Connecting the outer sleeve  210  at both ends may increase the bending stiffness and/or torsional stiffness of the adjustably flexible downhole tool  150 . 
     The free end  226  of the outer sleeve  210  may comprise a first interface surface  514  configured to interface with a second interface surface  516  of the actuating sleeve  500 . In the illustrated embodiment, the first interface surface  514  and the second interface surface  516  comprise tapered/angular surfaces. However, the first interface surface  514  and the second interface surface  516  may comprise any suitable interface for restraining radial and/or axial movement of the free end  226  of the outer sleeve  210 . For example, the first interface surface  514  may comprise at least one protrusion and the second interface surface  516  may comprise at least one recess configured to receive the at least one protrusion. 
     As set forth above with respect to  FIG.  5 A , the adjustably flexible downhole tool  150  may comprise the actuator  218  to move the actuating sleeve  500  from the first position to the second position. In the illustrated embodiment, the actuator  218  may comprise the electric motor  502  attached to a ball-screw mechanism  518 . The electric motor  502 , ball-screw mechanism  518 , and an associated power supply and electronics may be installed in the second connector end  206 . The electric motor  502  may drive ball-screw mechanism  518  to actuate the piston valve  504  (e.g., move a piston plug  520  along the piston valve housing  542 ) which may open the fluid line  506  to the sealed chamber  508 . After pressure in the sealed chamber  508  increased above a threshold pressure (e.g., wellbore pressure), a pressure differential between the sealed chamber  508  and the wellbore  102  may drive the actuating sleeve  500  to move to the second position. 
     In some embodiments, the actuator  218  may comprise the electric motor  502  attached to a hydraulic pump (not shown) that is configured to pump hydraulic oil from a reservoir into the sealed chamber  508 . The pressure from the hydraulic oil pumped into the sealed chamber may drive the actuating sleeve  500  to the second position. Further, the pressure in sealed chamber  508  may be controlled with a check valve/relief valve. A pressure transducer may monitor the pressure in sealed chamber  508 . In response to the pressure in the sealed chamber  508  falling lower than desired pressure, the electric motor  502  and hydraulic pump may be pump additional hydraulic oil into the sealed chamber  508  to restore the desired pressure to sealed chamber  508 . In response to pressure in the sealed chamber  508  exceeding a maximum desire pressure (e.g., due to thermal expansion of the hydraulic oil or from compression of sealed chamber  508  due to mechanical loading), the relief valve may vent a portion of the hydraulic oil back to the reservoir, which may reduce pressure in the sealed chamber  508 . 
     Moreover, the actuator  218  may be configured to drive the actuating sleeve  500  from the second position back to the first position. For example, a solenoid valve (not shown) may open to allow the hydraulic oil in the sealed chamber  508  to vent back to the reservoir. Further, the actuator  218  may comprise a biasing mechanism (not shown). The biasing mechanism may comprise a spring configured to apply a biasing force to the actuating sleeve  500  in a direction toward the first position. As the pressure in the sealed chamber  508  decreases, via the oil being vented, the actuation force on the actuating sleeve  500  from pressure in the sealed chamber may fall below the biasing force from the biasing spring, such that the biasing spring may drive the actuating sleeve  500  from the second position to the first position. As such, the actuator may selectively move the actuating sleeve between the first position and the second position to adjust the bending stiffness and/or torsional stiffness of the adjustably flexible downhole tool  150 . 
       FIG.  6    illustrates a cross-sectional view of an adjustably flexible downhole tool having a mechanical actuator configured to drive the actuating sleeve from the first position to the second position, in accordance with some embodiments of the present disclosure. As illustrated, the adjustably flexible downhole tool  150  may comprise the actuator  218  to drive the actuating sleeve  500  from the first position to the second position. The actuator  218  may comprise an electric motor  502  configured to drive a pinion gear  522  to rotate the actuating sleeve  500  via a ring gear/spline  524  such that the actuating sleeve  500  moves axially from the first position to the second position. In some embodiments, the actuating sleeve  500  may be threaded to the second connector end  206  of the adjustably flexible downhole tool  150 . As such, moving the actuating sleeve  500  may comprise rotating the actuating sleeve  500  with respect to the second connector end  206 . In some embodiments, the electric motor may be configured to drive the actuating sleeve  500  into the outer sleeve  210  with high axial force to generate an effective coupling of the actuating sleeve  500  to the outer sleeve  210  that resists separation under bending moments and/or other forces applied to the adjustably flexible downhole tool  150 . The high axial force may also resist deformation (e.g., ovalization) of the actuating sleeve  500  and the outer sleeve  210  in response to bending. 
     Moreover, as set forth above, the actuator  218  may be configured to drive the actuating sleeve  500  from the second position to the first position. In some embodiments, the electric motor  502  may operate in the reverse direction to move actuating sleeve  500  away from the outer sleeve  210  and back to the first position. As such, the actuator  218  may selectively move the actuating sleeve  500  between the first position and the second position to adjust the bending stiffness and/or torsional stiffness of the adjustably flexible downhole tool  150 . Indeed, the actuator  218  may alternate the actuating sleeve  500  between the first position and the second position as the bottom hole assembly  134  moves along the wellbore  102  based at least in part on a portion of the wellbore (e.g., straight portion or curved portion) through which the bottom hole assembly  134  is traveling. 
     Accordingly, the present disclosure may provide systems for adjusting bending stiffness and/or torsional stiffness of an adjustably flexible downhole tool as the bottom hole assembly moves through a wellbore. The claim may comprise any of the various features disclosed herein, including one or more of the following statements. 
     Statement 1. A system for an adjustably flexible downhole tool comprises first and second connector ends; a shaft extending between the first and second connector ends, wherein the shaft is configured to bend in response to passing through curved portions of a wellbore; an outer sleeve disposed around at least a portion of the shaft and extending from the first connector end in a direction toward the second connector end; and at least one adjustable member configured to move axially, with respect to the shaft, from a first position to a second position to increase bending stiffness and/or torsional stiffness of the adjustably flexible downhole tool, wherein the at least one adjustable member at least partially restrains bending of the shaft in the second position. 
     Statement 2. The system of statement 1, wherein the at least one adjustable member is disposed within an annulus formed between a radially outer surface of the shaft and a radially inner surface of the outer sleeve. 
     Statement 3. The system of statement 1 or statement 2, wherein the first position is disposed proximate the first connector end, and wherein the second position is disposed proximate the second connector end. 
     Statement 4. The system of any preceding statement, wherein the at least one adjustable member comprises an annular piston, wherein a radially inner piston surface of the annular piston interfaces with a radially outer shaft surface of the shaft and a radially outer piston surface of the annular piston interfaces with a radially inner sleeve surface of the outer sleeve, and wherein the annular piston at least partially restrains radial movement of the shaft with respect to the outer sleeve at a location of the annular piston. 
     Statement 5. The system of any preceding statement, further comprising a track disposed along a path of the at least one adjustable member from the first position to the second position, wherein the track is configured restrain rotational movement of the at least one adjustable member with respect to the shaft and the outer sleeve. 
     Statement 6. The system of any preceding statement, further comprising a debris barrier spanning between the shaft and the outer sleeve, wherein the debris barrier is configured to prevent downhole debris from moving into an annulus formed between the shaft and the outer sleeve. 
     Statement 7. The system of any preceding statement, further comprising a wedge disposed proximate the second position, wherein the wedge is configured to secure the at least one adjustable member at the second position. 
     Statement 8. The system of any preceding statement, further comprising a pivot guide disposed about the shaft proximate the second connector end, wherein the pivot guide is disposed between the shaft and the outer sleeve, and wherein the pivot guide comprises a spherical bearing, a crowned spline, or other constant velocity joint configured to pivot such that the shaft may radially deflect with respect to the outer sleeve. 
     Statement 9. The system of any of statements 1, 3, 5, or 6, wherein the at least one adjustable member comprises an actuating sleeve that is axially offset from the outer sleeve in the first position, and wherein the actuating sleeve is configured to interface with the outer sleeve to restrain bending of the shaft in the second position. 
     Statement 10. The system of statement 1 or statement 3, wherein the at least one adjustable member comprises a plurality of annular rings, wherein each annular ring of the plurality of annular rings is configured to interface with at least one adjacent annular ring, in the second position, to restrain bending of the shaft in the second position. 
     Statement 11. The system of any preceding statement, further comprising an actuator configured to drive the adjustable member to any position between the first position and the second position, wherein the actuator may be configured to drive the adjustable member forward toward the first position and/or in reverse toward the second position, and wherein the actuator comprises a hydraulic actuator, an electric motor, or some combination thereof. 
     Statement 12. A system for an adjustably flexible downhole tool comprises first and second connector ends; a shaft extending between the first and second connector ends, wherein the shaft is configured to bend in response to passing through curved portions of a wellbore; and a plurality of annular rings disposed about a radially outer surface of the shaft along a length of the shaft, wherein each annular ring of the plurality of annular rings is configured to move axially, with respect to the shaft, from a first position to a second position, and wherein each annular ring of the plurality of annular rings is configured to interface with at least one adjacent annular ring, in the second position, to at least partially restrain bending of the shaft and increase bending stiffness and/or torsional stiffness of the adjustably flexible downhole tool. 
     Statement 13. The system of statement 12, wherein each annular ring of the plurality of annular rings comprises a first interlocking feature at a first axial end of the annular ring and a second interlocking feature at a second axial end of the annular ring, wherein the first interlocking feature comprises a protrusion, and wherein the second interlocking feature comprises a recess. 
     Statement 14. The system of statement 12 or statement 13, further comprising a locking feature configured to axially hold the plurality of annular rings in the second position. 
     Statement 15. The system of any of statements 12-14, wherein the locking feature comprises threading, an expandable ring, a spring energized lock, collet, or some combination thereof. 
     Statement 16. The system of any of statements 12-15, further comprising a torsional locking feature configured to restrain rotational movement of the plurality of annular rings with respect to the shaft. 
     Statement 17. The system of any of statements 12-16, further comprising an actuator configured to drive the plurality of annular rings axially, with respect to the shaft, from the first position to the second position such that the plurality of annular rings are compressed toward each other. 
     Statement 18. A system for an adjustably flexible downhole tool comprises first and second connector ends; a shaft extending between the first and second connector ends, wherein the shaft is configured to bend in response to passing through curved portions of a wellbore; an outer sleeve disposed around at least a portion of the shaft and extending from the first connector end in a direction toward the second connector end; and an actuating sleeve coupled to the second connector end, wherein the actuating sleeve is configured to move axially, with respect to the shaft, from a first position to a second position, and wherein the actuating sleeve in configured to interface with outer sleeve in the second position to restrain bending of the shaft and increase bending stiffness and/or torsional stiffness of the adjustably flexible downhole tool. 
     Statement 19. The system of statement 18, further comprising a shear pin configured to hold the actuating sleeve in the first position, wherein the shear pin is configured to shear to release the actuating sleeve in response to an actuation force. 
     Statement 20. The system of statement 18 or statement 19, further comprising an actuator configured to drive the actuating sleeve from the first position to the second position, wherein the actuator comprises a hydraulic actuator, an electric motor, or some combination thereof. 
     Therefore, the present embodiments are well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present embodiments may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Although individual embodiments are discussed, all combinations of each embodiment are contemplated and covered by the disclosure. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present disclosure.