Patent Publication Number: US-9834992-B2

Title: Adjustment mechanisms for adjustable bent housings

Description:
The present application is a U.S. National Stage patent application of International Patent Application No. PCT/US2015/019039, filed on Mar. 5, 2015, the benefit of which is claimed and the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field of the Invention 
     The present disclosure relates generally to directional drilling, e.g., directional drilling for hydrocarbon recovery wells. More particularly, embodiments of the disclosure relate to systems, tools and methods employing an adjustable bent housing for controlling the direction in which a drilling bit cuts a wellbore. 
     2. Background Art 
     Directional drilling operations involve controlling the direction of a wellbore as it being drilled. The direction of a wellbore refers to both its inclination relative to vertical, and its azimuth or angle from true north or magnetic north. Usually the goal of directional chilling is to reach a target subterranean destination with a drill string. It is often necessary to adjust a direction of the drill string while directional drilling, either to accommodate a planned change in direction or to compensate for unintended and unwanted deflection of the wellbore. Unwanted deflection may result from a variety bottom hole assembly (BHA) and the techniques with which the wellbore is being drilled. 
     Some directional drilling techniques involve rotating a drill bit with a positive displacement motor (mud motor) and a bent housing included in the BHA. The BHA can be connected to a drill string or drill pipe extending from a surface location, and the mud motor can be powered by circulation of a fluid or “mud” supplied through the drill string. The BHA can be steered by sliding, e.g., operating the mud motor to rotate the drill bit without rotating the bent housing in the BHA. With the bend in the bent housing oriented in a specific direction, continued drilling causes a change in the wellbore direction. 
     When an adjustment in a drilling angle is necessary, the entire drill string may be removed from the wellbore in order to replace the bent housing with another bent housing that defines a different bend angle. In other instances, an adjustable bent housing may be provided that permits an adjustment to over a range of bend angles once the drill string is removed from the wellbore. It should be appreciated that removing the drill string to replace the bent housing or to adjust the bend angle can be expensive and time consuming. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is described in detail hereinafter on the basis of embodiments represented in the accompanying figures, in which: 
         FIG. 1  is a cross-sectional schematic side-view of a directional wellbore drilled with a BHA in accordance with example embodiments of the disclosure; 
         FIG. 2  is a schematic drawing of the BHA of  FIG. 1  having a bent housing including an adjustment mechanism for controlling a bend angle of the bent housing in accordance with example embodiments of the disclosure; 
         FIG. 3  is a cross-sectional schematic view of the bent housing of  FIG. 2  illustrating a plurality of support members of the adjustment mechanism; 
         FIG. 4  is a cross-sectional schematic view of an electromechanical actuator for the adjustment mechanism of  FIG. 3 ; 
         FIG. 5  is a cross-sectional schematic view of another bent housing having an externally disposed measurement mechanism for measuring the bend angle of the bent housing in accordance with example embodiments of the disclosure; 
         FIG. 6  is a cross-sectional schematic view of another bent housing having an internally disposed measurement mechanism in accordance with example embodiments of the disclosure; 
         FIGS. 7A through 7D  are cross-sectional schematic top-views of a bent housing in a wellbore illustrating a rotational progression of the bent housing during a directional drilling operation in accordance with example embodiments of the disclosure; 
         FIGS. 8A and 8B  are cross-sectional schematic views of a bent housing including one or more hydraulically actuated adjustment mechanisms in accordance with example embodiments of the disclosure: 
         FIG. 9  is a cross-sectional schematic view of bent housing including another hydraulically actuated adjustment mechanism employing a dual action piston in accordance with example embodiments of the disclosure; 
         FIG. 10  is a cross-sectional schematic view of a bent housing including a thermally actuated adjustment mechanism in accordance with example embodiments of the disclosure; 
         FIG. 11  is a cross-sectional schematic view of a bent housing including another thermally actuated adjustment mechanism in accordance with example embodiments of the disclosure; and 
         FIGS. 12A and 12B  are a flowchart illustrating an operational procedure for forming an adjustable drill string housing and operating the adjustable drill string housing in a directional drilling operation in accordance with example embodiments of the disclosure; 
         FIGS. 13A through 13C  are cross-sectional schematic side-view of a bent housing illustrating a procedure employing a sacrificial support member for altering a bend angle of the bent housing in accordance with exemplary embodiments of the disclosure; 
         FIG. 14A  is a schematic perspective view of a bent housing including a plurality of sacrificial support members supported between upper and lower flanges in accordance with other exemplary embodiments of the disclosure; 
         FIG. 14B  is of a schematic cross-sectional view of one of the sacrificial support embers of  FIG. 14A ; 
         FIG. 15  is a schematic cross-sectional view of a two-piece support member having a sacrificial connection mechanism in accordance with other exemplary embodiments of the disclosure; 
         FIG. 16A  is a schematic cross-sectional view of a galvanic corrosion system for a sacrificial support member in accordance with other exemplary embodiments of the disclosure; 
         FIG. 16B  is an enlarged cross-sectional view of a cathode sleeve member of the galvanic corrosion system of  FIG. 16A ; 
         FIGS. 17A through 17C  are schematic cross-sectional views of systems for inducing shear failure in sacrificial support members in accordance with other exemplary embodiments of the disclosure; 
         FIG. 18  is a schematic cross-sectional view of an electromechanical actuator for initiating failure of a sacrificial support member in accordance with exemplary embodiments of the disclosure; 
         FIG. 19  is a schematic cross-sectional view of a fluidic actuator for initiating failure of a sacrificial support member in accordance with other exemplary embodiments of the disclosure; 
         FIG. 20  is a schematic cross-sectional view of a mechanical actuator for initiating failure of a sacrificial support member in accordance with other exemplary embodiments of the disclosure; 
         FIGS. 21A and 21B  are schematic cross-sectional views of an adjustment mechanism including a latch member in respective latched and un-latched configurations in accordance with exemplary embodiments of the disclosure; 
         FIGS. 21C and 21D  are cross-sectional views of a mechanical and fluidic actuator respectively for moving the latch member of  FIGS. 21A and 21B  from the latched to un-latched configurations in accordance with the disclosure; 
         FIG. 22A  is a schematic cross-sectional view of an adjustment mechanism including a thermal actuator for inducing failure in a sacrificial support members in accordance with exemplary embodiments of the disclosure; 
         FIG. 22B  is an enlarged cross-sectional view of an insulated heating sleeve of the thermal actuator of  FIG. 22A ; 
         FIG. 23  is a cross-sectional side view of an adjustment mechanism including an explosive actuator for inducing failure in a sacrificial support member in accordance with exemplary embodiments of the disclosure; 
         FIGS. 24A and 24B  are side-views of adjustment mechanisms including longitudinally spaced support members in accordance with exemplary embodiments of the disclosure; 
         FIGS. 25A through 25D  are cross-sectional top-views of a bent housing illustrating a procedure for sequentially failing a plurality of support members to in accordance with exemplary embodiments of the disclosure; 
         FIGS. 26A and 26B  are a flowchart illustrating an operational procedure for forming and operating an adjustable drill string housing in accordance with example embodiments of the disclosure; 
         FIG. 27  is a cross-sectional schematic side-view of a bent housing including an energy delivery system operable to transfer energy from a remote location to a support member for triggering an adjustment in a bend angle of the bent housing according with example embodiments of the present disclosure; 
         FIGS. 28A and 28B  are partial perspective views of support members illustrating target areas thereon for receiving energy from the energy delivery system of  FIG. 27 ; 
         FIGS. 29A through 29C  are cross-sectional schematic side-views of energy delivery systems including a gate valve operable to selectively release a fluid from a reservoir; 
         FIGS. 30A through 30C  are cross-sectional schematic side-views of energy delivery systems including a puncturing tool for selectively releasing fluid from a reservoir; and 
         FIGS. 31A and 31B  are cross-sectional schematic side-views of an energy delivery system including a check valve for selectively releasing fluid from an internal passageway of a bent housing to a target area of a support member in accordance with example embodiments of the present disclosure; and 
         FIGS. 32A through 32C  are cross-sectional schematic side-views of a drill string illustrating a procedure for altering a bend angle of a drill string housing upon detection of a lateral casing window in accordance with exemplary embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the interest of clarity, not all features of an actual implementation or method are described in this specification. Also, the “exemplary” embodiments described herein refer to examples of the present invention. In the development of any such actual embodiment, numerous implementation-specific decisions may be made to achieve specific goals, which may vary from one implementation to another. Such would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. Further aspects and advantages of the various embodiments and related methods of the invention will become apparent from consideration of the following description and drawings. 
     The present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Further, spatially relative terms, such as “below,” “lower,” “above,” “upper,” “up-hole,” “down-hole,” “upstream,” “downstream,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the apparatus in use or operation in addition to the orientation depicted in the figures. 
       FIG. 1  illustrates a drilling system  10  for drilling a directional wellbore  12  in accordance with example embodiments of the disclosure. The wellbore  12  extends from a surface location “S” through a geologic formation “G” along a curved longitudinal axis X 1  to define a vertical section  12   a , a build section  12   b  and a tangent section  12   c . The tangent section  12   c  is the deepest section of the wellbore  12 , and generally exhibits lower build rates (changes in the inclination of the wellbore  12 ) than the build section  12   b.    
     A rotary drill bit  14  is provided at a down-hole location in the wellbore  12  (illustrated in the tangent section  12   c ) for cutting into the geologic formation “G.” A drill string  18  extends between the drill bit  14  and the surface location “S,” and in some exemplary embodiments, a bottom hole assembly (BHA)  20  is provided within the drill string  18  proximate the drill bit  14 . The BHA  20  can be operable to rotate the drill bit  14  with respect to the drill string  18 . The term “bottom hole assembly” or “BHA” may be used in this disclosure to describe various components and assemblies disposed proximate to the drill bit  14  at the down-hole end of drill string  18 . Examples of components and assemblies (not expressly illustrated in  FIG. 1 ) which may be included in the BHA  20  include, but are not limited to, a bent sub or housing, a mud motor, a near bit reamer, stabilizers, and other down hole instruments. Various types of well logging tools (not expressly shown) and other down-hole instruments associated with directional drilling of a wellbore  12  may also be included. 
     At a surface location “S” a drilling rig  22  is provided to facilitate drilling of the wellbore  12 . The drilling rig  22  includes a turntable  28  that rotates the drill string  18  and the drill bit  14  together about the longitudinal axis X 1 . The turntable  28  is selectively driven by an engine  30 , and can be locked to prohibit rotation of the drill string  18 . To rotate the drill bit  14  with respect to the drill string  18 , mud  36  can be circulated down-hole by mud pump  38 . The mud  36  is pumped through the drill string  18  and passed through a mud motor (not expressly illustrated in  FIG. 1 ) in the BHA to turn the drill bit  14 . The mud  36  can be expelled through openings (not shown) in the drill bit  14  to lubricate the drill bit  14 , and then returned to the surface location through an annulus  40  defined between the drill string and the geologic formation “G.” 
     Referring now to  FIG. 2 , the BHA  20  includes a housing  42  defining an upper end  44  and a lower end  46 . The main function of the housing  42  is to contain and protect the various components of the BHA  20 . The upper end  44  of the housing  42  is threaded to permit coupling the BHA  20  to the drill string  18  ( FIG. 1 ). Below the upper end  44  of the housing, a dump sub  48  is optionally provided in the BHA  20  to permit fluid flow between the drill string  18  ( FIG. 1 ) and the annulus  40  ( FIG. 1 ) in certain conditions when the BHA  20  is down-hole. A power unit  50  is provided below the dump sub  48  for generating rotational motion. In one or more exemplary embodiments, the power unit  50  comprises a progressive cavity positive displacement pump, which converts hydraulic energy into mechanical energy in the form of a rotating rotor (not shown) disposed therein. In some embodiments, the rotor can be induced to rotate eccentrically about an upper longitudinal axis X 2  by circulating mud  36  through the power unit  50 . In other embodiments, other types of down-hole motors, including electric motors, may be provided in the power unit  50  to provide the rotational energy. A transmission unit  52  is coupled to a lower end of the power unit  50  for transmitting rotational motion down-hole. In some embodiments, the transmission unit  52  may include a flexible drive shaft (see, e.g., constant velocity shaft  140  in  FIGS. 5 and 6 ), which receives eccentric rotational motion from the power unit  50 , and transmits concentric rotational motion (about longitudinal axis X 3 ) to a bearing assembly  54  coupled below the power unit  50 . The rotational motion generated in the power unit  50  can thus be transmitted to the drill bit  14  through the transmission unit  52  and the bearing assembly  54 . In the illustrated embodiment, a bent housing  100  couples the power unit  50  and transmission unit  52 . 
     Although the terms “bent housings” and “bent subs” are sometimes used synonymously, a “sub” is typically a bent section installed in the drill string  18  above the power unit used in the directional drilling of well bores. A “housing”, on the other hand, is generally interconnected between the power unit  50  and the bearing assembly and, in addition to providing an angular offset, also accommodates the drive shaft connecting the power unit  50  to the bearing assembly  54 . Although aspects of the present disclosure are described in terms of an adjustable drill housing or bent housing  100 , it should be appreciated that aspects of the disclosure may be practiced in a bent sub as well. The bent housing  100  defines a bend angle θ (see  FIG. 3 ) between the longitudinal axis X 2  of the portions of the BHA  20  above the bent housing  100  and a longitudinal axis X 3  of the portions of the BHA  20  below the bent housing  100 . In some example embodiments, one or more of the other components of the BHA  20  described above also comprises a bent housing.  100 . 
     Bent Housing with Adjustment Mechanisms 
     Referring to  FIG. 3 , bent housing  100  includes an annular member  102  and an internal passageway  104  extending therethrough. In some embodiments, the annular member  102  is prefabricated in a bent configuration either by physical bending or by a machining operation to create an angular offset. In some exemplary embodiments, the annular member  102  is constructed monolithically, e.g., from a single continuous piece of material, and in some other exemplary embodiments, the annular member  102  may be constructed of two or more bodies coupled to one another by threaded connectors, welding, or other coupling mechanisms to define upper and lower ends  102   a ,  102   b  of the annular member  102 . An angle θ may thereby be defined between the upper and lower longitudinal axes X 2  and X 3 , which extend thorough upper and lower ends  102   a ,  102   b  of the annular member  102 , respectively. An initial bend angle θ 0  in the range of about 0° to about 6° may be defined by the annular member  102  by the prefabrication process, although other initial bend angles θ 0  are contemplated within the scope of the present disclosure. 
     An adjustment mechanism  110  is provided for adjusting the bend angle θ. The bent housing  100  may be referred to as “down-hole adjustable” since the adjustment mechanism  110  is operable to adjust the bend angle θ while the bent housing  100  is in the wellbore  12  ( FIG. 1 ) without requiring that the bent housing  100  be withdrawn to the surface location “S.” The bent housing  100  is therefore distinguishable from “surface adjustable” bent housings, which are generally adjusted prior to insertion into the wellbore  12  and remain fixed until withdrawn and readjusted. As one skilled in the art will recognize, various aspects of the present disclosure may be practiced in connection with down-hole adjustable bent housings, with surface adjustable bent housings and/or both down-hole adjustable and surface adjustable bent housings. A bend axis X B  is defined through the intersection of the axes X 2  and X 3  and extends perpendicularly to longitudinal axes X 2  and X 3 . The bend axis X B  defines a longitudinal location of the angular offset in the bent housing  100 . 
     In some exemplary embodiments, an upper flange  116  extends radially outward from the annular member  102  at an up-hole location with respect to the bend axis X B . Similarly, a lower flange  118  extends from the annular member  102  at a down-hole location with respect to the bend axis X B . The upper and lower flanges  116 ,  118  can be formed integrally with the material of the annular member  102  or coupled thereto by fasteners, welding or other recognized construction methods. In some example embodiments, the annular flanges  116 ,  118  can extend radially around the entire annular wall  102 , and in some example embodiments, the flanges  116 ,  118  can be radially segmented such that the flanges  116 ,  118  protrude from the annular member  102  only at the radial location where support members  120  are disposed. Support members  120  (designated in  FIG. 3  as  120   a  and  120   b ) extend between the upper and lower flanges  116 ,  118 , and upper and lower ends  120   U  and  120   L  of the support members  120  are respectively supported thereby. Internal stresses can be selectively and adjustably imparted to the support members  120  to alter the bend angle θ. For example, the bend angle θ can be decreased by imparting a tensile stress in an interior-angle support member  120   a  and/or a compressive stress can be imparted to an exterior-angle support member  120   b . The tensile forces in the interior-angle support member  120   a  urge flanges  116 ,  118  toward one another in the direction of arrows A 1 , and the compressive forces urge flanges  116 ,  118  away from one another on a radially opposite side of the annular member  102  in the direction of arrows A 2 . The flanges  116 ,  118  are operable to transmit the internal stresses from the support members  120  to the annular member  102  to thereby alter the bend angle θ. The bend angle θ may similarly be decreased by imparting a tensile stress in the exterior-angle support member  120   b  and/or a compressive stress in the interior-angle support member  120   a.    
     The support members  120  may exhibit various geometries in various exemplary embodiments. For example the support members  120  may comprise threaded rods, solid cylinders, and hollow tubes. The support members  120  may include round or polygonal cross-sections, and may be generally curved or straight in a longitudinal direction. 
     Referring to  FIG. 4 , adjustment mechanism  110  further includes at least one actuator  122  for selectively imparting internal stresses to support the members  120 . In some embodiments, the actuator  122  comprises an electric motor  124  operably coupled to the support member  120  by a drive gear  126 , and a torque nut  128 . The drive gear  126  may be fastened to a shaft  124   a  of the electric motor  124 , and may be induced to rotate therewith in response to activation of the electric motor  124 . An outer diameter of the torque nut  128  engages the drive gear  124  such that rotational motion may be communicated between the drive gear  124  and the torque nut  128 . Rotational motion of the torque nut  128  with respect to the upper flange  116  is supported by a pair of thrust bearings  130  disposed on opposite sides to the torque nut  128  and within a recess  116 ′ defined within the upper flange  116 . An inner diameter of the torque nut  128  is threaded onto the upper end  120   U  of the support member  120  such that rotational motion of the torque nut  128  induces generally longitudinal motion of the support member  120  with respect to the upper flange  116 . Thus, the electric motor  124  may be activated to drive the upper end  120   U  of the support member  120  in the longitudinal directions of arrows A 3  and A 4  with respect to the upper flange  116 . The lower end  120   L  ( FIG. 3 ) of the support member  120  may be fixedly fastened to the lower flange  118  ( FIG. 3 ) such that the longitudinal movement of the upper end  120   U  of the support member  120  imparts tensile or compressive stresses to the support member  120 , and thereby alters the bend angle θ ( FIG. 3 ). 
     In some exemplary embodiments, a protective cover  132  may be provided over the adjustment mechanism  110 . The protective cover  132  can be attached to the annular member  102  and/or the upper and lower flanges  116 ,  118  in a manner that is permits the upper and lower flanges  116 ,  118  to move toward and away from one another as the bend angle θ is adjusted. Together with the annular member  102 , the protective cover  132  may define a sealed chamber in which a lubricant, insulating fluid, or other specialized chemical solution “C” may be maintained. The chemical solution “C” may be an anti-corrosive of other fluid selected to prevent premature failure of the support member  120 . In some embodiments, the specialized chemical solution “C” may comprise an electrolyte fluid “E” ( FIG. 16A ) to facilitate failure of a support member  332  ( FIG. 16A ) as described below. In some embodiments, the protective cover  132  may act as a stabilizer or offset pad that engages the geologic formation “G” ( FIG. 1 ). 
     Analyses have been performed to determine characteristics associated with altering the bend angle θ with the adjustment mechanism  110 . A simulated tensile load of 100,000 lbs. was applied between the upper and lower flanges  116  and  118  of a mathematical model of the annular member  102 . The simulated load was applied at a radial distance of 2.5 inches from the axes X 2  and X 3 , thus simulating a tensile load in an interior-angle support member  120   a . A change in the bend angle θ of 0.4° was observed in the model. To achieve a 0.4° change in the bend angle θ, an electric motor  124  can be selected that is capable of producing 500 in-lbs. of torque or more. A gear ratio of 12:1 between the torque nut  128  and the drive gear  126  was determined to permit the electric motor  124  to generate sufficient stress in the interior-angle support member  120   a.    
     To achieve the same 0.4° change in the bend angle θ, complimentary tensile and compressive loads of 50,000 lbs. were simulated in support members  120  disposed on opposing radial sides of the annular member. The simulated support members  120  were supported between upper and lower flanges  116  and  118  at the radial positions of the interior-angle support member  120   a  and the exterior-angle support member  120   b . It was determined that a motor capable of generating approximately 225 in-lbs. of torque could produce the 50,000 lbs. compressive and tensile loads. 
     In some exemplary embodiments, the actuator  122  is remotely operable from the surface location “S” ( FIG. 1 ). The actuator  122  may include a control unit  134  having a communication unit  134   a , and a controller  134   b . The communication unit  134   a  may facilitate communication between the actuator  122  and the surface location “S” or other down-hole components. The communication unit  134   a  can provide a bi-directional telemetry system employing any combination of wired or wireless communication technologies. In some embodiments, the communication unit  134   a  can produce a short hop EM signal that can be communicated within the wellbore  12  ( FIG. 1 ) across the power unit  50  ( FIG. 2 ), to a mud pulser (not shown) or similar tool for may transmit the signal to the surface location “S.” In some embodiments, the communication unit  134   a  can include a switch (not shown) that is responsive to objects dropped from the surface location “S” such as balls, darts, RFID tags, etc. to trigger operation of the electric motor  124 . In other embodiments, the communication unit  134   a  can receive signals from sensors or other feedback devices (not shown) disposed in the wellbore  12  ( FIG. 1 ). The signals may be representative of down-hole parameters such as temperature or pressure in the wellbore  12  ( FIG. 1 ). The electric motor  124  may then be triggered when the down-hole parameters are determined to be within a predetermined range. 
     The actuator  122  may also include controller  134   b  operably coupled to the electric motor  124  and the communication unit  134   a . In some embodiments, the controller  134   b  may include a processor  134   a  and a computer readable medium  134   b  operably coupled thereto. The computer readable medium  64   b  can include a nonvolatile or non-transitory memory with data and instructions that are accessible to the processor  134   a  and executable thereby. In one or more embodiments, the computer readable medium  134   b  is pre-programmed with predetermined triggers for actuating or deactivating the electric motor  124 , and may also be pre-programmed with predetermined sequences of instructions for operating the electric motor  124  in response to triggers received by the communication unit. 
     Referring now to  FIG. 5 , exemplary embodiments of a measurement mechanism  138  for measuring the bend angle θ of the bent housing  100  are illustrated. In some exemplary embodiments, the measurement mechanism  138  operates independently of adjustment mechanism  110  ( FIG. 4 ) to measure a physical characteristic of the bent housing  100 . The annular member  102  of the bent housing  100  is illustrated with a constant velocity (CV) shaft  140  extending therethrough. A feedback device  142  is supported between the upper and lower flanges  116 ,  118  and is operable to provide a signal from which the bend angle θ is determinable or estimable. In one or more exemplary embodiments, the feedback device  142  is operable to provide a signal representative of a longitudinal distance D 1 , or a change in the longitudinal distance D 1 , between the upper and lower flanges  116 ,  118 , or a change in a longitudinal length of the support members  120  ( FIG. 4 ). For example, in some exemplary embodiments, the feedback device  142  can comprise a potentiometer or a linear variable differential transformer (LVDT). In some embodiments, feedback devices  142  may be incorporated into one or more of the support members  120  ( FIG. 4 ), or feedback devices  142  may be provided independently of the support members  120  ( FIG. 4 ). Since a change in the bend angle θ is associated with a corresponding change in the longitudinal distance D 1 , the bend angle θ may be determined from the signal provided by the feedback device  142 . 
     In some exemplary embodiments, the feedback device  142  can be electrically coupled in an electrical circuit that includes the communication unit  134   a , controller  134   b  ( FIG. 4 ) and a power source  144 . In some embodiments, power source  144  may comprise a battery, or a self-contained turbine operable to generate electricity responsive to the flow of wellbore fluids therethrough. In some embodiments, power source  144  comprises a connection with the surface location “S,” e.g., an electric or hydraulic connection to the surface location through which power for the feedback device  142 , communication unit  134   a  and/or controller  134   b  may be provided. In some embodiments, the controller  134   b  may be preprogrammed with instructions thereon for determining a bend angle θ from signals received from the feedback device  142 . The instructions may include instructions to transmit the bend angle θ to the surface location “S” via the communication unit  134   a , and or instructions to operate the electric motor  124  ( FIG. 4 ) based on the bend angle θ determined. 
     Referring to  FIG. 6 , another exemplary embodiment of a measurement mechanism  148  includes a feedback device  152  disposed on an interior of the annular member  102 , e.g., within the internal passageway  104 . The feedback device  152  is supported between a reference beam  154  and an interior surface  156  of the annular member  102 . In some embodiments, the reference beam  154  may be a substantially rigid member fixedly coupled to the interior surface  156 , such that the reference beam  154  extends generally parallel with longitudinal axis X 2 . The reference beam  154  overhangs the bend axis X B  such that a change in the bend angle θ corresponds to a change in a distance D 2  between an end of the reference beam  154  and the interior surface  156 . The feedback device  152  may comprise any of the mechanisms described above for the feedback device  142  ( FIG. 5 ) and may similarly be coupled can be electrically coupled in an electrical circuit that includes the communication unit  134   a , controller  134   b  and a power source  144  ( FIG. 5 ). The feedback device  152  may thus be operable to provide confirmation or error signals to the surface location to indicate a status of the adjustment mechanism  110  ( FIG. 4 ). 
     Referring now to  FIGS. 7A through 7D , a plurality of radially spaced adjustment mechanisms  110  may be employed to influence a drilling direction of the drill string  18  to which the bent housing  100  is coupled. A clockwise rotational progression of the bent housing  100  with respect to a coordinate axis  156  is illustrated as indicated by arrow A 5 . The rotational progression may be intentionally induced from the surface location “S” ( FIG. 1 ), e.g., with the turn table  28  ( FIG. 1 ), or the progression may be inadvertently induced by characteristics of the geologic formation “G” contacting the drill string  18 . 
     The bent housing  100  is initially arranged in the wellbore  12  as illustrated in  FIG. 7A . To build in a positive y-direction, the support member  120   a  may be placed in tension while the support member  120   b  is placed in compression. The bent housing  100  will then have a bias to bend in the y-direction about the bend axis X B . When the bent housing  100  arrives at the orientation of  FIG. 7B , support members  120   a  and  120   d  may be placed in tension while support members  120   b  and  120   c  are placed in compression. Similarly, when the bent housing  100  reaches the orientation of  FIG. 7C , support member  120   d  may be placed in tension while support member and  120   c  is placed in compression, and when the bent housing  100  reaches the orientation of  FIG. 7D , support members  120   b  and  120   d  may be placed in tension while support members  120   a  and  120   c  are placed in compression. In this manner, the bent housing  100  may be continuously or continually adjusted to maintain the bias to bend in the positive y-direction as throughout the rotational progression. In some exemplary embodiments the internal forces within the support members  120 , e.g., the tensile and compressive forces, may be adjusted as the bent housing  100  is in motion along the rotational progression. Constant and real time adjustments may be made in this manner to maintain the bias to bend in the desired direction. It should be appreciated that although four support members  120   a  through  120   d  are illustrated, more or fewer support members  120  may be provided without departing from the scope of the present disclosure. 
     In some exemplary embodiments, a feedback device  158  may be provided for determining an orientation of the bent housing  110  in the wellbore  12 . The feedback device  158  may comprise an inclinometer or similar tool. In some embodiments, the feedback device  158  may be operably coupled to the control unit  134  ( FIG. 4 ) of the adjustment mechanisms  110 , and the control units  134  may be preprogrammed with instructions for operating the actuators  122  ( FIG. 4 ) to impart the appropriate tensile and compressive loads to the support members  120   a  through  120   d  based on the orientation determined by the feedback device  158 . 
     Referring now to  FIGS. 8A and 8B , an adjustment mechanism  160  for altering the bend angle θ is illustrated. The adjustment mechanism  160  includes a hydraulic actuator  162  having a chamber  164  for hydraulic fluid “H” and a piston  166  disposed between upper and lower flanges  116 ,  118  on an interior-angle radial side of the annular member  102 . In some exemplary embodiments, a fixed quantity of hydraulic fluid “H” is sealed within the chamber  164 . An increase in the pressure and volume of the hydraulic fluid “H” urges the piston  166  toward the upper flange  116  in the direction of arrow A 6 , thereby placing the piston  166  in compression and urging the upper and lower flanges  116 ,  118  away from one another, and thereby decreasing the bend angle θ. The compressive stresses in the piston  166  are transferred through the flanges  116 ,  118  to the annular member  102 , and thus, the piston  166  serves as a support member  120 . Since down-hole temperatures generally increase with depth, and since increasing temperatures will induce an increase of the pressure and temperature in the hydraulic fluid “H,” the adjustment mechanism  160  may decrease the bend angle θ as the wellbore  12  ( FIG. 1 ) is drilled deeper. Increasing temperatures will generally increase a volume of the hydraulic fluid “H,” and resistance to volume changes generates an increase in pressure of the hydraulic fluid “H,” In some example embodiments, the adjustment mechanism  160  may automatically decrease the bend angle θ to guide the wellbore  12  ( FIG. 1 ) from the build section  12   b  ( FIG. 1 ) to the tangent section  12   c  ( FIG. 1 ) with generally lower build rates. This automatic change in the bend angle θ could permit the entire wellbore  12  ( FIG. 1 ) to be drilled in sliding mode, e.g., by operation of the power unit  50  ( FIG. 2 ) to rotate the drill bit  14  ( FIG. 2 ) without rotation of the entire drill string  18  ( FIG. 1 ) from the surface location “S” ( FIG. 1 ). Operation of the drill bit  14  ( FIG. 2 ) in the sliding mode rather than a rotating mode may significantly decrease operational alternating stresses throughout the drill string  18  ( FIG. 1 ), and thereby produce reliability improvements. 
     In one or more other embodiments, the chamber  164  is fluidly coupled to a reservoir  168 , which may be filled with a high pressure supply of hydraulic fluid “H” or a pump (not shown) may be coupled to the reservoir to pressurize the reservoir. A valve  170  is disposed between the chamber  164  and the reservoir  168 . The valve  170  may be remotely operable to selectively permit hydraulic fluid “H” to flow from the reservoir  168  to the chamber  164 . In one or more exemplary embodiments, the valve  170  may be coupled to the communication unit  134   a  ( FIG. 4 ) and the controller  134   b  ( FIG. 4 ) to permit remote operation from the surface location “S” ( FIG. 1 ) and/or operation according to a predetermined set of instructions programmed into the controller  134   b  ( FIG. 4 ). To decrease bend angle θ, the valve  170  may be opened to permit hydraulic fluid “H” to flow into the chamber  164 , to thereby urge the piston  166  in the direction of arrow A 6 , and to thereby urging the upper and lower flanges  116 ,  118  away from one another. 
     Although the adjustment mechanism  160  is described in terms of decreasing the angle θ, the adjustment mechanism  160  may also be employed to increase the bend angle θ. For example, in some embodiments, the piston  166  and chamber  164  may additionally or alternatively be disposed on an exterior-angle radial side of the annular member  102  (illustrated in  FIG. 8B ). As described above, separating the upper and lower flanges  116 ,  118  on an exterior-angle radial side of the annular member  102  may serve to increase the bend angle θ. 
     In other example embodiments, as illustrated in  FIG. 9 , an adjustment mechanism  172  may include a hydraulic actuator  174  with a “double acting” piston  176 . The double acting piston  176  is disposed in a chamber  178 , and axially divides the chamber  178  into two fluidly isolated sub-chambers  178   a ,  178   b . Each sub-chamber  178   a ,  178   b  is fluidly coupled to the reservoir  168 . Valves  170  ( FIG. 8 ), pumps (not shown) or other mechanisms may be coupled between the sub-chambers  178   a ,  178   b  and the reservoir  168  such that hydraulic fluid “H” may be selectively withdrawn from either sub-chamber  178   a  or  178   b , and simultaneously provided to the other sub-chamber,  178   a  or  178   b . The hydraulic fluid “H” imparts a force to a first face  176   a  of the piston  176  to urge the piston  176  in the direction of arrow A 7  and thereby urge the upper and lower flanges  116 ,  118  toward one another. Similarly, the hydraulic fluid “H” imparts a force to a second face  176   b  of the piston  176  to urge the piston  176  in the direction of arrow A 8  and thereby urge the upper and lower flanges  116 ,  118  away from one another. Thus, the dual acting piston  176  may be operable to both increase and decrease the bend angle θ ( FIG. 8 ). 
     Referring now to  FIG. 10 , an adjustment mechanism  180  for altering the bend angle θ is illustrated. The adjustment mechanism  180  includes a thermal actuator  182 . The thermal actuator  182  includes a support member  120  disposed between the upper and lower flanges  116 ,  118 . In some exemplary embodiments, the support member  120  is constructed at least partially of a shape memory alloy such as Nitinol. The support member  120  may thus be operable to change shape between at least first and second operational configurations responsive to at least a threshold temperature change. For example, the first configuration of the support member  120  may be a curved, bent or deformed configuration, which is maintained at a relatively low temperature. The second operational configuration can be a relatively straight configuration (as illustrated in phantom), which is maintained at a relatively high temperature. In some exemplary embodiments, the support member  120  may transition between the first and second operational configurations at a transition temperature in the range of about 150° C. to about 160° C. Since the support member  120  will exhibit a relatively lesser length in the first curved configuration than in the second straight configuration, the support member  120  may be moved between the first and second operational configurations to urge the upper and lower flanges  116 ,  118  toward and away from one another, respectively. In one or more example embodiments of operation, the change between the first and second operational configurations can be triggered by an increase in the down-hole temperature as the wellbore  12  ( FIG. 1 ) is drilled to deeper depths. 
     In one or more embodiments, the thermal actuator  182  may include a heating circuit  184  for selectively inducing the support member  120  to change between the first and second operational configurations. In some embodiments, the heating circuit  184  may include the communication unit  134   a , controller  134   b  and power source  144 . In some embodiments, the heating circuit  184  may comprise a cartridge heater having a heating element  186  extending through or adjacent the support member  120 . In some exemplary embodiments, the heating element  186  may be a resistive heating element. In some other exemplary embodiments, the material of the support member  120  may be coupled in the heating circuit, and may thus serve as a resistive heating element. In operation, a current I can be selectively induced to flow through the heating circuit  184  to heat the support member  120  to above the transition temperature, and thereby induce the support member  120  to change from the first configuration to the second operational configuration. The current I may be interrupted to allow the support member  120  to cool and return to the first configuration. In other exemplary embodiments, the heating element  186  may comprise an induction heating coil arranged to heat the support member  120  by electromagnetic induction. An alternating current may be supplied through the heating element  186  to induce eddy currents in the support member to generate heat therein. 
     Referring now to  FIG. 11 , an adjustment mechanism  190  for altering the bend angle θ is illustrated. The adjustment mechanism  190  includes a thermal actuator  192  with an interior-angle support member  120   e  and an-exterior angle support member  120   f.    
     In some exemplary embodiments, the interior support member  120   e  may comprise a solid structure that is responsive to heat to expand to separate the flanges  116 ,  118 . In some other exemplary embodiments, the interior-angle support member  120   e  includes an inner support member  120   e ′ (illustrated in phantom) and an outer expansion sleeve  120   e ″ disposed around the inner support member  120   e ′. The inner support member  120   e ′ may be secured to the upper and lower flanges  116 ,  118  in a floating manner that permits relative movement of the upper and lower flanges  116 ,  118  toward and away from one another about the bending axis X B . The outer expansion sleeve  120   e ″ is constructed of a material having a dissimilar coefficient of thermal expansion α with respect to the annular member  102 . For example, in some exemplary embodiments, the outer expansion sleeve  120   e ″ may have a higher coefficient of thermal expansion α than the annular member  102 . In some embodiments, the annular member  102  may be constructed of a steel alloy having a coefficient of thermal expansion α STEEL  of about 7.3×10 −6  in/in ° F. and the expansion sleeve  120   e ″ may be constructed of beryllium copper having a coefficient of thermal expansion α BECU  of about 9.6×10 −6  in/in ° F. Thus, when the adjustment mechanism  190  is exposed to increasing temperatures, e.g., the increasing temperatures associated with drilling wellbore  12  ( FIG. 1 ) to increasing depths, the expansion sleeve  120   e ″ will expand to a greater degree than the annular member  102 . Since the expansion sleeve  120   e ″ is disposed between interior surfaces of the upper and lower flanges  116 ,  118 , this expansion causes the expansion sleeve  120   e ″ to exert an outwardly directed force on the upper and lower flanges  116 ,  118  in the direction of arrows A 9 . Since this outwardly directed force is imparted to the upper and lower flanges  116 ,  118  on an interior-angle side of the annular member  102 , the bend angle θ is decreased. 
     The exterior-angle support member  120   f  may also be arranged for decreasing the bend angle θ. The exterior-angle support member  120   f  includes an inner support member  120   f ′ and an outer expansion sleeve  120   f ″. The inner support member  120   f ′ extends between the upper flange  116 , through lower flange  118  and to a torque nut  194  threaded or otherwise affixed to an end of inner support member  120   f ′. The outer expansion sleeve  120   f ″ is disposed over the inner support member  120   f ′ and extends longitudinally between the torque nut  194  and a longitudinally exterior surface of the lower flange  118 . Where the outer expansion sleeve  120   f ′ has a coefficient of thermal expansion α greater than that of the annular member  102 , exposing the adjustment mechanism  190  to increasing temperatures operates to cause the expansion sleeve  120   f ′ to exert an outwardly directed force on the lower flange  118  and the torque nut  194  in the directions of arrows A 10 . Since the torque nut  194  is threaded to an end of the inner support member  120   f ′, the force applied to the torque nut  194  is transferred through the inner support member  120   f ′ to the upper flange  116 , thereby drawing the upper flange  116  toward the lower flange in the direction of arrow A 11 . The upper and lower flanges  116 ,  118  are thereby urged toward one another on the exterior-angle side of the annular member  102 , thereby decreasing the bend angle θ. 
     In other exemplary embodiments, expansion sleeves  120   e ″ and  120   f ″ may be arranged to increase the bend angle θ. For example, the radial positions of the expansion sleeves  120   e ″ and  120   f ″ may be reversed to cause the upper and lower flanges  116 ,  118  to be approximated on the interior angle side of the annular member  102  and separated on the exterior angle side of annular member  102 . In some embodiments, the expansion sleeves  120   e ″ and  120   f ″ are arranged to impart forces of differing magnitudes to the upper and lower flanges  116 ,  118 . In some embodiments, an external heat source, such as the heater  184  ( FIG. 10 ), may be provided to impart external heat to the expansion sleeves  120   e ″ and  120   f ″. In other embodiments, the expansion sleeves  120   e ″ and  120   f ″ can have coefficients of thermal expansion α that are lower than the annular member  102 . 
     Referring to  FIGS. 12A and 12B , an operational procedure  200  illustrates example embodiments of drilling a wellbore  12  ( FIG. 1 ) with an adjustable bent housing  100  ( FIG. 2 ). Initially, at step  202 , a well profile is planned through the geologic formation “G.” The well profile can be based on available geologic data to avoid obstacles, to reach a planned destination, or to achieve other objectives. Next, at step  204 , the well profile and the a BHA  20  are modeled to determine the required bend angle θ or range of bend angles θ required for forming the wellbore  12 . The expected side loads on the drill bit  14  and the BHA  20  may also be evaluated in step  204 . Next, an initial bend angle θ 0  for the BHA can be selected based on the planned well profile and the expected lateral loads. An annular member  102  having the selected initial bend angle θ 0  may then be machined. Next, the forces required bend the annular member  102  to one or more adjusted bend angles θ are determined at step  208 . The adjusted bend angles θ may facilitate achieving the planned well profile. Next, the support members  120  are designed based on the determined forces. The design of the support members  120  may also accommodate additional forces, such as weight on bit, lateral loads and backbend loads, expected to be transferred the support members  120 . In some embodiments, the support members  120  can be designed to maintain all forces in the support members  120  and the annular member  102  in an elastic range such that the BHA  20  may be reused. Next, at step  212 , the support members  120  may be installed on the annular member  102 , and preloaded. In some exemplary embodiments, an appropriate preload can be applied by adjusting the position of a torque nut  128 ,  194  on the support member  120 . 
     Next, drilling may be initiated at step  214  with a drill string  18  ( FIG. 1 ) provided with the BHA  20  supported at an end thereof. In one or more exemplary embodiments, the drilling may be initiated with the initial bend angle θ 0  in the BHA  20 . At decision  216 , the actual well profile of wellbore  12  being drilled is evaluated and compared to planned well profile to determine whether an adjustment to the bend angle θ would facilitate following the planned well profile. In some embodiments, at decision  216 , a radial orientation of the annular member  102  in the wellbore  12  is determined, e.g., by querying feedback device  158  ( FIG. 7A ). The radial orientation of the annular member  102  in the wellbore  12  may facilitate determining whether the adjustment to the bend angle θ would facilitate following the planned well profile. In some exemplary embodiments, a selection of the radial support member  120  in which to trigger the changes in internal stresses from a plurality of support members  120  radially spaced around the annular member  120  is based on the radial orientation of the annular member  102  in the wellbore  12 . If it is determined at decision  216  that an adjustment to the bend angle θ would facilitate following the planned well profile, the procedure  200  proceeds to step  218 . 
     At step  218 , an adjustment to the bend angle θ is triggered. In one or more exemplary embodiments, the adjustment to the bend angle θ can be triggered by transmitting an instruction signal to the communication unit  134   a  ( FIG. 4 ) that may be recognized by the controller  134   b . In response to receiving the instruction signal, the controller  134   b  may initiate a predetermined sequence of instructions stored thereon, which cause an actuator  122 ,  162 ,  174 ,  182 ,  192  to adjust the bend angle θ. For example, in various exemplary embodiments, the controller  134   b  may instruct the electric motor  124  ( FIG. 4 ) to operate, the valve  170  ( FIG. 8 ) to open, the piston  176  ( FIG. 9 ) to move, and/or, the heating circuit  184  ( FIG. 10 ) to operate to induce a change in the bend angle θ as described above. Next at step,  220  the adjusted bend angle θ may be verified. For example, in some embodiments, the controller  134   b  may query a measurement mechanism  138 ,  148  for an indication that the intended bend angle θ was achieved. Once it is verified that the intended bend angle θ was achieved drilling can continue (step  222 ). When it is determined at decision  216  that no adjustment is required, the procedure  200  may proceed directly to step  222 , where drilling continues with the bend angle θ in existing configuration. 
     The procedure  200  can then proceed to step  224  where the bend angle is reevaluated. In some exemplary embodiments, the bend angle θ can be continuously or continually monitored and adjusted by returning to decision  216  as often as necessary to maintain drilling along the planned well profile. Once the wellbore  12  reaches its intended destination, the procedure  200  may end at step  226  and the wellbore  12  may be completed. 
     Sacrificial Support Members 
     Referring generally to  FIGS. 13-26 , devices, mechanisms and methods are illustrated for altering the bend angle of an adjustable drill-string housing by “sacrificing” a support member or a portion thereof at a down-hole location. In exemplary embodiments, the support members may maintain a preload in an annular member of the drill-string housing, and the preload may be released by inducing the support member to fail. The “failure” of the sacrificial support member may include various failure modes such as failure in tension, compression, torsion, shear, buckling, or other structural failures. In some embodiments, failure of a sacrificial support member may be induced by changing down-hole loads on the drill string, e.g., applying weight on bit, applying a torque to the drill string, and applying pressure through the drill string. In other embodiments, failure may be induced with actuators described below. Although sacrificing support members is generally described herein in terms of a structural failure of the sacrificial support member, as used herein, “failure” may include other processes that may be irreversible down-hole. For example, it should be appreciated that in some exemplary embodiments, the sacrificial support members may be induced to fail by un-fastening or rearranging a select component such that sacrificial support member no longer maintains the internal preload in the annular member. Thereafter, the select component may be refurbished or reset at a surface location “S” ( FIG. 1 ) for subsequent use in the adjustable drill string housing. 
     Referring to  FIGS. 13A through 13C , bent housing  300  includes annular member  102  defining internal passageway  104  extending therethrough. As described above, the annular member  102  may be prefabricated with an initial bend angle θ 0  ( FIG. 13A ) between the upper and lower longitudinal axes X 2  and X 3 , which extend thorough upper and lower ends  102   a ,  102   b  of the annular member  102 , respectively. Once constructed, the annular member  102  may be preloaded or pre-stressed to deform the annular member  102  to a first operational configuration with a first operational bend angle θ 1  ( FIG. 13B ). A sacrificial support member  302  is affixed to the annular member  102  and extends across the bend axis X B  to maintain the annular member  102  in the first operational configuration. The sacrificial support member  302  is removable down-hole to relieve at least a portion of the preload and permit the annular member  102  to relax toward a second operational configuration with second operational bend angle θ 2  ( FIG. 13C ). As illustrated, the sacrificial support member  302  is affixed to an interior-angle (α 1 ) radial side of the annular member  102 , and wedges the annular member  102  toward the first operational configuration in the direction of arrows A 12 . Thus the first operational bend angle θ 1  is less than the initial bend angle θ 0 . In some exemplary embodiments, the second operational bend angle θ 2  may be equal to the initial bend angle θ 0 . 
     In some exemplary embodiments, the sacrificial support member  302  may be constructed of at least one disintegrating material  302   a ,  302   b , and/or  302   c . The disintegrating material  302   a ,  302   b ,  302   c  may include sintered metallic powder compacts and/or non-metallic materials such as ceramics. The disintegrating materials  302   a ,  302   b ,  302   c  may be dissolveable or corroded in drilling fluids such as mud  36  ( FIG. 1 ), or may be induced to disintegrate when exposed to a different trigger fluid. In some embodiments, the trigger fluid may be produced with a specialized trigger chemical (not shown) added to the mud  36 . In some exemplary embodiments, each of the disintegrating materials  302   a ,  302   b ,  302   c  may be induced to disintegrate in response to the addition of a different trigger chemical such that a particular disintegrating material  302   a ,  302   b ,  302   c  may be selected for disintegration. Each of the disintegrating materials  302   a ,  302   b ,  302   c  extend over a different respective angular span α a , α b , α c  within the interior angle α I . The disintegration of any one of the disintegrating materials  302   a ,  302   b ,  302   c  permits the annular member  102  to relax a different amount in the direction of arrows A 13  toward the second operational configuration. For example, disintegration of disintegrating material  302   b  while disintegrating materials  302   a  and  302   c  remain intact, may permit the annular member  102  to relax to an intermediate configuration between the first and second operational configurations wherein the bend angle θ is between the first and second operational bend angles θ 1  and θ 2 . In some exemplary embodiments, the disintegrating materials  302   a ,  302   b ,  302   c  may be sequentially dissolved to move the annular member to a plurality of intermediate configurations between the first and second operational configurations. 
     In other embodiments (not shown), disintegrating materials  302   a ,  302   b ,  302   c  may be placed in other locations on the annular member  102  such as within the internal passageway  104 , within an exterior angle α E  or at other radial locations around the annular member  102 . It should be appreciated that the placement of a disintegrating material  302   a ,  302   b ,  302   c  at different radial locations may permit selective bending of the annular member  102  about axes other than the bend axis X B  illustrated. 
     Referring to  FIGS. 14A and 14B , bent housing  310  includes a plurality of sacrificial support members  320  disposed radially about the annular member  102 . In some embodiments, twelve (12) sacrificial support members may be provided between the upper and lower flanges  116 ,  118  of the annular member  102 . Each of the sacrificial support members  320  may be individually induced to fail down-hole to move the annular member  102  to at least thirteen different operational configurations. A torque nut  324  is threaded onto each end of the sacrificial support members  320 . The torque nuts  324  may be tightened or loosened to adjust the preload on the annular member  102 . In some exemplary embodiments, a stress concentrator such as an annular groove  326  is provided in the support member  320  and defines a weakest point in the sacrificial support member  320 . The support members  320  may be induced to fail at the annular groove  326  to relieve a portion of the preload applied by the torque nuts  324 , and thereby adjust the bend angle θ of the annular member  102 . 
     In some exemplary embodiments, the support members  320  may be induced to fail by the selective application of a trigger fluid or chemical to selectively induce corrosion of the sacrificial support member  320 . In embodiments where the corrosion of the sacrificial support member  320  are described to induce failure in the sacrificial support member  320 , any structural material of the sacrificial support member  320  may be characterized as a disintegrable material. In other embodiments, the sacrificial support members may be induced to fail by the application of sufficient loads to the sacrificial support members  320 . For example, an operator may apply weight on bit with the annular member  102 . In a particular orientation in the wellbore  12  ( FIG. 1 ) to induce failure of at least one of the sacrificial support members  320 . In other embodiments, the support members  320  may be selectively induced to fail by any of the techniques described herein below. 
     Referring to  FIG. 15 , a sacrificial support member  328  includes first and second portions  328   a  and  328   b  connected to one another with a bonding material  328   c . The bonding material  328   c  may be constructed of a dissimilar material with respect to the first and second portions  328   a ,  326   h  such that the bonding material  328   c  may be induced to corrode more rapidly than the first and second portions  328   a ,  328   b . For example, the bonding material may be constructed of any of the disintegrating materials  302   a ,  302   b ,  302   c  ( FIG. 13B ), and the first and second portions  328   a ,  328   b  may be constructed of stainless steel. In other embodiments, the first and second portions  328   a ,  328   b  may be coupled to one another by welding, brazing, soldering or a similar process, and the bonding material  328   c  may comprise a zinc-based solder. Corrosion of the bonding material  328   c  may disconnect the first and second portions  328   a ,  326   b  from one another, thereby relieving a preload from the annular member  102  ( FIG. 14B ). 
     In some embodiments, the bonding material  328   c  may alternatively or additionally be employed to bond the sacrificial support member  328  to the upper and lower flanges  116 ,  118  ( FIG. 14B ) or to another part of the annular member  102  ( FIG. 14B ). Corrosion of the bonding material  328   c  may thus disconnect the sacrificial support member  328  from the upper and lower flanges  116 ,  118  to thereby relieve at least a portion of the preload from the annular member  102  ( FIG. 14B ). In some other embodiments, the bonding material  328   c  may serve as sacrificial anode in a galvanic corrosion system  330  ( FIG. 16A ) as described below. 
     Referring to  FIG. 16A , galvanic corrosion system  330  includes a sacrificial support member  332  extending between upper and lower flanges  116 ,  118 , which maintains a pre-load in the annular member  102 . A cathode member  334  is arranged as a sleeve disposed around the sacrificial support member  332  (anode), and is constructed of a material having a different electrolytic potential than the sacrificial support member  332 . Thus, when the sacrificial support member  332  and the cathode member  334  are submerged in an electrolyte fluid “E,” an ion migration from the sacrificial support member  332  to the cathode member  334  accelerates the corrosion of the sacrificial support member  332 . In some exemplary embodiments, the electrolyte fluid “E” may include drilling mud  36  ( FIG. 1 ), or a specialized chemical solution “C” ( FIG. 4 ) disposed under a protective cover  132  ( FIG. 4 ). In some embodiments, an acidic electrolyte fluid “E” may be provided to accelerate a controlled corrosion of the sacrificial support member  332 . In some exemplary embodiments, the electrolyte fluid “E” may also comprise basic fluids and/or salts. 
     In some exemplary embodiments, the cathode member  334  may be eliminated, and the flanges  116 ,  118  and/or the annular member  102  may serve as the cathode. In some embodiments, a current source  336  may be electrically coupled between sacrificial support member  332  and the cathode member  334  to impress a current I through the sacrificial support member  332 , cathode member  334  and electrolyte “E.” The current source  336  may include a direct current sources such as a battery, and the current I may further accelerate corrosion of the sacrificial support member  332 , or in some embodiments, prevent corrosion of the sacrificial support member  332 . In some exemplary embodiments, the communication unit  134   a , controller  134   b  may be coupled to the current source  336  such that the current I may be selectively induced and interrupted from the surface location “S” ( FIG. 1 ). In some exemplary embodiments, the controller  134   b  may include instructions for selectively connecting, disconnecting and/or reversing the polarity of the current source  336 . 
     Referring to  FIG. 16B , in some embodiments, the sacrificial support member  332  includes a protective coating  332   a  disposed around an exterior surface thereof. The protective coating  332   a  may comprise a stainless steel tube or other structure that is more resistant to corrosion than a core  332   b  of the sacrificial support member  332 . In some embodiments, the protective coating  332   a  includes at least one of paint, rubber, epoxy and a passive oxide film layer. The core  332   b  may be exposed to the electrolyte fluid “E” through one or more openings  338  defined in the protective coating  332   a  adjacent the cathode member  334 . In some embodiments, stress concentrators  340  such as annular grooves may be positioned within the openings  338 . The openings  338  and the stress concentrators  340  promote localized corrosion of the core  332   b  adjacent the cathode member  334  to thereby accelerate failure of the sacrificial support member  332 . In some instances, the failure of sacrificial support member  332  at the stress concentrators  340  may be induced over a timespan of about an hour or less after inducing current I. In other instances, the current I may be induced for several hours to complete the failure of the sacrificial support member  332 , which might otherwise take months or years to complete without the current I. In some embodiments, the protective coating  332   a  is selected to wear off the sacrificial support member  332  by inducing contact between the sacrificial support member  332  and the geologic formation “G” ( FIG. 1 ) and or casing (see, e.g., casing  606  in  FIG. 32A ) in the wellbore  12  ( FIG. 1 ). 
     Referring now to  FIGS. 17A through 17C , galvanic corrosion or other methods for inducing failure in sacrificial support members  344  may be employed to selectively induce shear failure in the sacrificial support members  344 . It should be appreciated that the sacrificial support members  344  may be sufficiently robust to withstand a preload “P” ( FIG. 17C ) and any expected operational loads, while being sufficiently vulnerable to an intentionally induced failure to permit an expedient transition between first and second operational configurations of a tubular member  102 ′,  102 ″. Since shear failure is often more susceptible to stress concentration and other factors, the support members  344  may often be induced to fail more rapidly than a support member, e.g., support member  332  ( FIG. 16A ) subject primarily to compressive or tensile longitudinal forces. 
     In some exemplary embodiments, sacrificial support members  344  may be elongate, cylindrically-shaped or pin-shaped members that extend generally parallel to the bending axis X B . The sacrificial support members  344  may be arranged to extend through a pair of overlapping upper and lower flanges  116 ′,  118 ′ ( FIG. 17A ) or through one or more plate members  346  ( FIGS. 17B and 17C ) that extend between longitudinally spaced upper and lower flanges  116 ″  118 ″. Thus, the preload “P” applied to the respective annular members  102 ′,  102 ″ to achieve a particular first operational bend angle θ 1  is manifest as shear forces in the sacrificial support members  344 . 
     As illustrated in  FIG. 17C , the sacrificial support member  344  may serve as a sacrificial anode in a galvanic corrosion system  350 . The sacrificial support member  344  may be electrically coupled to circuitry  352  including the communication unit  134   a , controller  134   b  and current source  336  ( FIG. 16A ). The circuitry  352  may also be coupled to plate member  346 . The sacrificial support member  344  may be constructed of a material such as zinc, which has a greater electrolytic potential than the plate member  346 . In some exemplary embodiments, the plate member  346  may be constructed of stainless steel. The sacrificial support member  344  may thus be induced to corrode and fail to relieve the preload “P.” and thereby move the annular member  102 ″ to a second operational configuration down-hole. 
     Referring to  FIGS. 18-20 , actuators  356 ,  358  and  360  may be employed to initiate and/or accelerate corrosive failure of sacrificial support members  362 . In some embodiments, the actuators  356 ,  358  and  360  may be employed to selectively penetrate a protective coating  362   a  that protects a core  362   b  of the sacrificial support member  362  from a corrosive environment. The protective coating  362   a  may include paint, rubber and/or epoxies. In some exemplary embodiments, the core  362   b  may be constructed of an iron material that is highly susceptible to corrosion by a chemical solution “C,” such as a dilute nitric acid. The protective coating  362   a  may be a passive oxide layer pre-applied to the iron core  362   b  by exposing the iron core  362   b  to a relatively strong nitric acid solution. In operation, the protective coating  362   a  can be maintained intact in the chemical solution “C,” and thus, the annular member  102  may be maintained in the first operational configuration. The chemical solution “C” may be contained under protective cover  132  ( FIGS. 18 and 19 ) and/or exposed to the drilling mud  36 . When an adjustment of the annular member  102  to a second operational configuration is desired, the actuator  356 ,  358  and  360  may be remotely controlled to mechanically cut, scratch, score, grind, scrape or abrade protective coating  362   a  down-hole. The core  362   b  may thereby be exposed to the chemical solution “C,” and can be permitted to corrode until the sacrificial support member  362  fails. 
     The actuator  356  ( FIG. 18 ) may include an electric motor  356   a  coupled to an abrasive medium  356   b  such as a grinding wheel, wire brush or sand paper arranged to engage the sacrificial support member  362 . The electric motor  356   a  may be operatively coupled to the communication unit  134   a  and controller  134   b  for activation, or may be operatively coupled to a driveshaft (not shown) of a mud powered turbine or power unit  50  (see  FIG. 2 ) through a clutch (not shown) or other mechanism. 
     In some other exemplary embodiments, the actuator  358  ( FIG. 19 ) may include a control valve  358   a  disposed within a fluid passageway extending from the internal passageway  104  or another source of a pressurized and/or abrasive fluid. The control valve  358   a  may be opened to divert a flow mud  36  from the internal passageway  104  toward the sacrificial support member  362 . The flow of mud  36  may be continued to abrade the protective coating  362   a  from the sacrificial support member  362 , or may be continued until the sacrificial support member  362  fails. In one or more exemplary embodiments, the control valve  358   a  is operatively coupled to the communication unit  134   a  and controller  134   b , and may be electronically actuated thereby. In some other embodiments, the control valve  358   a  may be operated by a pressure or temperature controlled piston (not shown), such that the control valve  358   a  may be operated in response to predetermined down-hole conditions. 
     In one or more other exemplary embodiments, the actuator  360  ( FIG. 20 ) may include a linkage  360   a  coupled to the annular member  102  and extending into the internal passageway  104 . The linkage  360   a  includes a cutting tool  360   b  extending toward the sacrificial support member  362 . The cutting tool  360   b  may be operable to scrape the protective coating  362   a  from the sacrificial support member  362  in response to an object  360   c , such as a ball or dart, moving through the internal passageway  104 . In other exemplary embodiments, the linkage may be electronically or hydraulically actuated by a solenoid or piston (not shown). 
     Any of the actuators  356 ,  358  and  360  may be employed in conjunction with a galvanic corrosion system  330  ( FIG. 16A ) to accelerate the corrosion of the core  362   a  of the sacrificial support member  362 . In some embodiments, any of the actuators  356 ,  358  and  360  may be employed with or without the galvanic corrosion system  330  to penetrate an external surface of the sacrificial support member  362  to structurally weaken, fully sever, buckle or otherwise induce failure of the sacrificial support member  362 . 
     Referring to  FIG. 21A through 21D , a sacrificial support member a  366  is illustrated with a latch  366   a  disposed at least one end thereof. The sacrificial support member  366  is operable to maintain a preload “P” in the annular member  102  while disposed in a latched position ( FIG. 21A ). In the latched position, the latch  366   a  may be engaged with the upper flange  116  as illustrated, and latched or fixedly coupled at a lower end (not shown) thereof to the lower flange  118  ( FIG. 14A ). Thus, in the latched position, the sacrificial support member  366  may be maintained in tension by the preload “P to maintain the annular member  102  in a first operational configuration. The latch  366   a  is selectively movable to an unlatched position ( FIG. 21B ) to relieve the preload “P” and move the annular member  102  to a second operational configuration. 
     Various actuators may be provided to move the latch  366   a  from the latched position to the unlatched position one time while down-hole. In some embodiments, the latch  366   a  and the sacrificial support member  366  remain intact, and do not necessarily structurally or mechanically fail when moved to the unlatched position. Thus, the sacrificial support member  366  may be returned to the latched position, e.g., by returning the annular member  102  to the surface location “S” ( FIG. 1 ), or by applying an appropriate weight on bit. As used herein, however, the term “failure” may include moving the latch  366   a  to the unlatched position at a down-hole location. 
     As illustrated in  FIG. 21C , an actuator  368  for moving the latch  366   a  from the latched to unlatched position may include a linkage  368   a  operatively coupled to the latch  366   a  and responsive to an object  368   b  moving through the internal passageway  104 . The object  368   b  may include a ball, dart or other mass dropped through the drill string  18  ( FIG. 1 ) from the surface location “S” ( FIG. 1 ), and operates to engage the linkage  368   a  and push the linkage  368  radially outward to release the latch  366   a.    
     As illustrated in  FIG. 21D , an actuator  370  may be provided for moving the latch  366   a  from the latched to unlatched position. The actuator  370  includes a piston  372  operably coupled to the latch  366   a  and responsive to a pressure differential between internal passageway  104  and the annulus  40 . The piston  372  has a first pressure surface  372 ′ in fluid communication with the internal passageway  104  through a passage  374  extending radially through the annular member  102 . Thus, a fluid pressure within the internal passageway  104  pushes the piston  372  radially outward. The piston  372  has a second pressure face  372 ″ in fluid communication with the annulus  40  such that a fluid pressure in the annulus  40  pushes the piston  372  radially inward. In operation, to transition the annular member  102  from the first operational configuration to the second operational configuration, an operator may increase the pressure in the internal passageway  104  to push the piston  372  and the latch  366   a  radially outwardly, and thereby release the latch  366   a  from the upper flange  116 . In some embodiments, an operator at the surface location may increase the pressure in the internal passageway  104  by employing the mud pump  38  ( FIG. 1 ) to increase the pressure of mud being pumped down-hole through the internal passageway  104 . 
     Referring generally to  FIGS. 22A through 23 , thermal actuators may be employed to apply heat to sacrificial support members  380  to selectively induce failure therein. Thermal and structural analyses have been performed indicating that about a 10% reduction in yield strength may be observed by increasing the temperature of a steel member by about 350° C. from room temperature, e.g., about 2.2° C. Additional heating further reduces the yield strength at higher rates. In one or more exemplary embodiments, a sacrificial support member  380  may be designed with a safety factor of 1.1 to withstand the expected loading under normal operating conditions. When the bend angle θ is to be adjusted, the sacrificial support member  380  may be sufficiently heated to weaken the sacrificial support member  380  such that continued operation will cause failure of the sacrificial support member  380 . In some embodiments, heat provided from the down-hole environment may be directed and/or be focused to the sacrificial support member  380 , and in some embodiments, once the sacrificial support member  380  is sufficiently heated and weakened, a supplementary force may be supplied to facilitate failure of the sacrificial support member  380 . For example, any of the actuators  356 ,  358  and  360  ( FIGS. 18, 19 and 20 , respectively) may be employed in conjunction with a thermal actuator described below. 
     As illustrated in  FIGS. 22A and 22B , an actuator  382  may include a thermal sleeve  384  disposed on or adjacent the sacrificial support member  380 . The thermal sleeve  384  may be selectively operated to produce and/or release heat to the sacrificial support member  380  and thereby structurally weaken the sacrificial support member  380 . In some exemplary embodiments, the thermal sleeve  384  comprises a resistive heating element or coil that converts electricity passing therethrough into heat. In other embodiments, the thermal sleeve  384  may comprise an induction coil that excites eddy currents in the sacrificial support member  380  in response to an alternating current flowing through the thermal sleeve. The thermal sleeve  384  may be operably coupled to current source  336 , communication unit  134   a , and controller  134   b . In some embodiments, the controller  134   b  includes a switch (not shown) that is operable from the surface location “S” ( FIG. 1 ) to permit an operator to selectively trigger the thermal sleeve  384 . To prevent heat loss from the sacrificial support member  380 , a thermal insulation layer  386  may be provided over the thermal sleeve  384 . The insulation layer  386  may extend over any portion of the sacrificial support member  380 , or over the entire longitudinal length of the sacrificial support member  380 . 
     Analysis has illustrated that where the sacrificial support member  380  is constructed of a cylindrical steel rod having a diameter of about 0.865 inches (about 22 mm) and a length of about 6.0 inches (15.2 cm), about 72.5 kJ are needed to induce a temperature change of 350° C. in the sacrificial support member  380 . Where the current source  336  is a 24V battery, 72.5 kJ of heat may be generated with a 5 Amp current over a period of about 10 minutes. This timeframe is much less than would be required to withdraw the annular member  102  from the wellbore  12  ( FIG. 1 ) to make an adjustment to the bend angle θ. 
     In other embodiments, the thermal sleeve  384  may comprise a thermite sleeve, which undergoes an exothermic oxidation reaction when ignited. In some embodiments, the oxidation reaction may release sufficient heat to fully sever the sacrificial support member  380 , e.g., by heating the support member  380  to or above the melting point of the material from which the sacrificial support member  380  is constructed. In some embodiments, the oxidation reaction may release sufficient heat to weaken the sacrificial support member  380  to facilitate failure of the sacrificial support member  380  with a supplementary force. Thermite materials generally include a fuel such as aluminum, magnesium, titanium, zinc, silicon and boron, and also generally include an oxidizer such as boron oxide, silicon oxide, magnesium oxide iron oxide and copper oxide. The thermite material may be formed into the thermal sleeve  384 , or may be contained within a tubular structure coupled to the sacrificial support member  380 . Since the ignition temperature of a thermite material is generally high, in some embodiments, the thermal sleeve  384  may comprise a strip of magnesium ribbon to facilitate ignition of the thermite material. The strip of magnesium ribbon may be operatively coupled to the current source  336 , communication unit  134   a , and/or controller  134   b  for selective ignition thereof. In some exemplary embodiments, the magnesium ribbon may be selectively ignited with an electrically operated igniter (not shown), and heat generated from the ignited magnesium may be directed toward the thermite material for ignition thereof. 
     Although thermite materials are not generally explosive, in some embodiments, the thermal sleeve  384  may additionally or alternatively comprise an explosive material. As illustrated in  FIG. 23 , a controlled explosion may be induced to cause or facilitate failure of the sacrificial support member  380 . In some embodiments, an explosive material may be incorporated into a thermal sleeve  384 , and may include a shaped charge directed at the sacrificial support member  380 . In some embodiments, a pyrotechnic pin or bolt may be employed. A pyrotechnic pin or bolt may be arranged in any manner that sacrificial support members  344  ( FIGS. 17A through 17C ) are arranged. The explosive material has been described herein as being incorporated into a “thermal” sleeve. However, one skilled in the art will recognize that a controlled explosion may generally impart mechanical force (pressure) to the sacrificial support member  380  to induce failure of the sacrificial support member  380 , rather than inducing failure by the application of heat. 
     Where a controlled explosion is employed, a blast shield  388  may be coupled to the annular member  102  to isolate the effects of the explosion from the wellbore  12  ( FIG. 1 ) and other components of the BHA  20 . A first end  388   a  of the blast shield  388  may be pinned or longitudinally fixed with respect to the annular member  102  and a second end  388   b  may be coupled by a roller connection or other mechanism that allows for at least one generally longitudinal degree of freedom between the blast shield  388  and the annular member  102 . Thus, the blast shield  388  will not impede deflection of the annular member  102  when the sacrificial support member  380  is caused to fail. The blast shield  388  may include, be part of, or share functionality with the protective cover  132  ( FIG. 4 ) discussed above. 
     Referring now to  FIG. 24A , an annular member  102  may define a plurality of bend angles θ a , θ b , θ c  . . . θ n  therein. Each of the bend angles θ a , θ b , θ c  . . . θ n  may be disposed along longitudinal axis X 1  and contribute to an overall or total bend angle θ t . Individual sets of upper flanges  116   a ,  116   b ,  116   c  . . .  116   n  (collectively or generally  116 ) and lower flanges  118   a ,  118   b ,  118   c  . . .  118   n  are provided on opposite longitudinal sides of each of the respective bend angles θ a , θ b , θ c  . . . θ n . Any of the support members described above, e.g., support members  120 ,  302 ,  320 ,  328 ,  332 ,  344   362 ,  366   380  (collectively or generally  120 ), may be provided between the flanges  116 ,  118 . The longitudinally spaced support members  120  may each support a portion of a preload applied to the annular member  102 . 
     According to at least one example simulated loading arrangement, a tensile pre-load of 50,000 lbs. may be maintained between upper and lower flanges  116   a ,  118   a  together with a tensile pre-load of 50,000 lbs. maintained between upper and lower flanges  116   b ,  118   b . This loading arrangement may achieve a change in the total bend angle θ t  similar to the 0.4° change in the bend angle θ described above, which was achieved with the simulated tensile load of 100,000 lbs. Although the total loading is the same, localized stresses in the annular member  102  may be reduced by distributing the loading over the plurality of bend angles θ a , θ b  or over a larger longitudinal length of the annular member  102 . In some exemplary embodiments, distributing the pre-load in this manner may facilitate maintaining stresses in the annular member  102  within an elastic range throughout the use of the annular member  102 , and may permit larger operating loads (weight on bit, etc.) to be applied to a drill string  18  ( FIG. 1 ). In some exemplary embodiments, distributing the loading may permit a greater total bend angle θ t  to be achieved. Also, in one or more exemplary embodiments, each of the support members  120  may be individually adjusted or induced to fail according to any of the methods and mechanisms described above such that the total bend angle bend angle θ t  may be adjusted. 
     As illustrated in  FIG. 24B , in some exemplary embodiments a plurality of bend angles θ a , θ b , θ c  . . . θ n  may be defined in an annular member having an arrangement of nested upper and lower flanges  116 ,  118 . At least one support member  120  is provided between upper flange  116   a  and lower flange  118   a  to maintain a pre-load in the annular member  102  and to define the bend angle θ a . Similarly, at least one support member  120  is provided between upper flange  116   b  and lower flange  118   b  to maintain a pre-load in the annular member  102  and to define the bend angle θ b . The upper flange  116   b  is disposed longitudinally between the upper and lower flanges  116   a ,  118   a , and thus the support members  120  at least partially overlap in a longitudinal direction. This nested arrangement may permit the bend angles θ a , θ b , θ c  . . . θ n  to be disposed relatively close to one another in a longitudinal direction, and may permit the total bend angle θ t  to be defined in a relatively short annular member  102  with respect to the arrangement illustrated in  FIG. 24A . 
     Referring now to  FIGS. 25A through 25D , a plurality of radially spaced sacrificial support members  120   a ,  120   b  and  120   c  may be employed to influence the orientation of a bend axis X B  defined in an annular member  102 , and permit an adjustment of the bend angle θ. Initially, as illustrated in  FIG. 25A , each of the sacrificial support members  120   a ,  120   b  and  120   c  may be loaded in a balanced manner such that no deflection or bend angle is defined in the annular member  102 . In some exemplary embodiments, each of the sacrificial support members  120   a ,  120   b  and  120   c  may be equally spaced around the annular member  102 , and may be preloaded to impart an equal tensile load on upper and lower flanges  116 ,  118  ( FIG. 14A ). With the annular member  102  in a generally straight configuration, a vertical section  12   a  of a wellbore  12  ( FIG. 1 ) may be expediently drilled. 
     When a bend angle θ is to be defined in the annular member  102 , e.g., to facilitate drilling a build section  12   b  of the wellbore  12  ( FIG. 1 ), one or more of the sacrificial support members  120   a ,  120   b  and  120   c  may be induced to fail to thereby unbalance the pre-load on the annular member  102 . For example, as illustrated in  FIG. 25B , a single sacrificial support member  120   b  may be induced to fail (as indicated by the “X” mark) to relieve a portion of the preload on the annular member  102 . Since the sacrificial support members  120   a  and  120   c  remain intact and continue to maintain a portion of the preload on the annular member  102 , the annular member  102  is induced to bend about bend axis X 3  in a direction of arrow A 14  extending between the support members  120   a ,  120   c . Under some loading arrangements, a first exemplary adjusted bend angle θ of about 0.7° may be established when the single sacrificial support member  120   b  is induced to fail. In some embodiments, the annular member  102  may be rotated (e.g. with the turntable  28  ( FIG. 1 ) to orient the bend angle θ within the wellbore  12  ( FIG. 1 ) to facilitate drilling in a particular direction. 
     If the first adjusted bend angle θ of about 0.7° is appropriate, drilling of the build section  12   b  of the wellbore  12  ( FIG. 1 ) may proceed. If the first adjusted bend angle θ of about 0.7° is too aggressive, a second exemplary adjusted bend angle θ may be established by selectively inducing a second sacrificial support member  120   c  to fail. As illustrated in  FIG. 25C , when sacrificial support members  120   b  and  120   c  are induced to fail and sacrificial support member  120   a  remains intact, the annular member  102  is induced to bend about bend axis X B  in a direction of arrow A 15  extending toward the support member  120   a . Under some loading arrangements, the second exemplary adjusted bend angle θ may be about 0.4°. If appropriate, the build section  12   b  of the wellbore  12  ( FIG. 1 ) may be drilled with the annular member  102  adjusted to the second adjusted bend angle θ. 
     When the build section  12   b  of the wellbore  12  ( FIG. 1 ) is complete, the annular member  102  may be returned to the generally straight configuration to facilitate drilling the tangent section  12   c  of the wellbore  12  ( FIG. 1 ). As illustrated in  25 D, each of the sacrificial support members  120   a ,  120   b ,  120   c  may be induced to fail to rebalance the loading on the annular member  102 , e.g., by relieving the preload in each radial direction. 
     In some exemplary embodiments, additional sets of radially spaced sacrificial support members  120  (not shown) may be provided on an annular member  102  such that the adjustment of the bend angle θ described with reference to  FIGS. 25A through 25D  may be repeated. It should also be appreciated that the adjustment of the bend angle θ described with reference to  FIGS. 25A through 25D  may also be implemented by employing the adjustment mechanism  110  ( FIG. 4 ) or any of the other adjustment mechanisms described above. 
     Referring now to  FIGS. 26A and 26B , an operational procedure  400  illustrates example embodiments of drilling a wellbore  12  ( FIG. 1 ) with an adjustable bent housing  100  ( FIG. 2 ). The operational procedure  400  is similar to the operational procedure  200  ( FIG. 12 ), but differs at least in that adjustments to the bend angle θ are implemented by selectively inducing failure in a sacrificial support member  120 , or by activating another mechanism to implement an irreversible or one-time release of a preload imparted to an annular member  102 . 
     Initially, at step  402 , a well profile is planned through the geologic formation “G,” and at step  404 , the well profile, the a BHA  20  and the expected operational loads are modeled to determine the required bend angle θ or range of bend angles θ required for forming the wellbore  12 . Next, an initial bend angle θ 0  for the BHA can be selected based on the planned well profile and the expected operational loads, and an annular member  102  having the selected initial bend angle θ 0  may be machined (step  406 ). Next, at step  408 , the preload required to bend the annular member  102  to a deformed operational configuration shape is determined. One or more sacrificial support members  120  are designed (step  410 ) and installed (step  412 ) to maintain the annular member in the deformed operational configuration. In some embodiments, the support members  120  can be designed to maintain all forces in the support members  120  and the annular member  102  in an elastic range such that the BHA  20  may be reused. 
     Next, drilling may be initiated at step  414  with a drill string  18  ( FIG. 1 ) provided with the BHA  20  supported at an end thereof. In one or more exemplary embodiments, the drilling may be initiated with the annular member  102  in the deformed operational configuration. At decision  416 , the actual well profile of wellbore  12  being drilled is evaluated and compared to planned well profile to determine whether an adjustment to the bend angle θ would facilitate following the planned well profile. 
     When it is determined at decision  416  that no adjustment is required, the procedure  400  may proceed to step  418 , where drilling continues with the annular member  102  in the deformed operational configuration. If it is determined at decision  416  that an adjustment to the bend angle θ would facilitate following the planned well profile, the procedure  400  proceeds to step  420 . At step  420 , an adjustment to the bend angle θ is triggered. In one or more exemplary embodiments, an adjustment mechanism is triggered to induce failure in the one or more sacrificial support members  120 . The actuator may be employed to implement one or more of inducing disintegration of one or more of the disintegrating materials  302   a ,  302   b ,  302   c  ( FIG. 13B ), triggering corrosion of the disintegrable material or sacrificial support member  120  with a galvanic corrosion system  330  ( FIG. 16A ), mechanically cutting the sacrificial support member  120  with an electric motor  316   a  ( FIG. 18 ), unlatching a latch  366   a  ( FIGS. 21A through 21D ), and/or employing any of the other mechanisms described herein. In one or more exemplary embodiments, inducing a failure in the one or more sacrificial support members  120  includes penetrating an exterior surface of the at least one sacrificial support member with a mechanical actuator, e.g., actuators  356  ( FIG. 18 ),  358  ( FIG. 19 ) and  360  ( FIG. 20 ) to thereby structurally weaken or cut the sacrificial support member  120 . In some exemplary embodiments a current source may be activated or interrupted to accelerate corrosion of the disintegrable material. 
     In some exemplary embodiments, inducing failure in the one or more sacrificial support members  120  may include applying compressive forces to the sacrificial support members  120 , e.g., by employing the electric motor  124  ( FIG. 4 ), or  172  to thereby induce buckling in the sacrificial support members. Next at step  422  the sacrificial support member  120  is permitted to fail, and the adjusted bend angle θ may be verified, e.g., by employing measurement mechanisms  138 ,  148 . Drilling may then continue (step  424 ) along the planned well profile. 
     In some exemplary embodiments, the procedure  400  may return to decision step  416  from step  422  and/or step  424 . For example, each of a plurality of sacrificial support members  120  may be individually induced to fail. A first sacrificial support member may be induced to fail while a second sacrificial support member remains intact. Subsequently, the second sacrificial support member  120  may be induced to fail to provide an additional bend angle θ, if it is determined at decision step  416  that additional adjustments are to be made. 
     Energy Delivery Systems for Adjustable Bent Housings 
     Referring now to  FIG. 27 , a bent drill string housing  500  includes an energy delivery system  502  for initiating or enhancing an adjustment of the bend angle θ defined by the annular member  102 . To facilitate the adjustment in the bend angle θ, the energy delivery system  502  may deliver energy to a support member  504  to induce failure of the support member  504  and thereby release a preload in the annular member  102  as described above. The energy delivery system  502  comprises an energy reservoir  506  for an energy source coupled to the drill string housing  500  and disposed at a remote location with respect to a support member  504 . The energy reservoir  506  may be disposed at a down-hole location with respect to the support member  504  as illustrated in  FIG. 27 , or any other remote location on the drill string housing  500 . The remote location of the energy reservoir  506  facilitates relatively unimpeded flow of drilling mud  36  ( FIG. 1 ) or other fluids around the drill string housing  500 . 
     In some exemplary embodiments, the energy reservoir  506  contains a fluid such as the chemical solution “C.” The chemical solution “C” may comprise a corrosion accelerant containing oxygen molecules, hydrogen ions and other metallic ions. As described above, in some exemplary embodiments, the chemical solution “C” may comprise a corrosion accelerant such as nitric acid. The energy delivery system  502  may be operable to selectively deliver the chemical solution “C” to a sealed, semi-sealed or unsealed corrosion chamber  510  defined between upper and lower flanges  116 ,  118 . In some embodiments, protective cover  132  may form a seal or partial seal with the upper and lower flanges  116 ,  118 . 
     An initiator is provided that is selectively operable to promote fluid flow through a fluid conduit  514  extending between the energy reservoir  506  and the corrosion chamber  510 . In some embodiments, the initiator may include an electric pump  512  operatively coupled to communication unit  134   a  and controller  134   b  to permit selective activation of the electric pump  512  from a surface location “S” ( FIG. 1 ). 
     In exemplary embodiments of operation, when an adjustment to the bend angle θ is to be implemented, an instruction signal may be transmitted from the surface location “S” ( FIG. 1 ) to the communication unit  134   a  that may be recognized by the controller  134   b . In response to receiving the instruction signal, the controller  134   b  may initiate a predetermined sequence of instructions stored thereon, which cause the electric pump  512  to operate to deliver the chemical solution “C” to the corrosion chamber  510 . The rate at which the chemical solution “C” is delivered to the corrosion chamber  510  may be regulated by the electric pump  512  and controller  134   b  to control the rate of corrosion of the support member  504 . Corrosion of the support member  504  is thereby accelerated, and the support member  504  may be permitted to fail. At least a portion of a preload maintained in the annular member  102  may thereby be released to adjust the bend angle θ. The adjusted bend angle θ may be verified, e.g., by querying a measurement mechanism  138 ,  148  ( FIGS. 5 and 6 ). In response to verifying the adjustment to the bend angle θ, the predetermined sequence of instructions may adjust operation of the pump  512 , e.g., to slow or cease operation thereof. 
     To further accelerate failure of the support member  504  by corrosion, a target area  514  may be defined on the support member  504  as illustrated in  FIGS. 28A and 28B . The corrosive chemical reactions may be concentrated at the target area  514  rather than distributed over an entire surface area of the support member  504  to accelerate failure of the support member  504 . The target area  504  may be arranged as an annular band circumscribing the support member  504  to facilitate corrosion in multiple directions around the support member  504 . As illustrated in  FIG. 28B , the annular band may be comprise a plurality of discrete regions  514   a ,  514   b  radially spaced from one another around the support member  504 . In some embodiments, the target area  514  may be constructed of a material, or coated with a material, that is matched with the particular chemical solution “C” delivered by the electric pump  504 . For example, the target are  514  may comprise a passive oxide layer as described above with reference to  FIGS. 18-20 ). In some embodiments, the target area  514  may be coated with a coating that degrades when exposed to the chemical solution “C,” and a remainder  516  of the surface area of the support member  504  may be coated with a material that is resistant to corrosion when exposed the chemical solution “C.” 
     Referring to  FIGS. 29A through 29C , the initiator of the energy delivery system  502  may include a remotely actuated valve  520   a ,  520   b ,  520   c  operable to release the chemical solution “C” from the energy reservoir  506 . As illustrated in  FIG. 29A , in some exemplary embodiments, the remotely actuated valve  520   a  may comprise an electromechanical actuator  522  operably coupled to the communication unit  134   a  and controller  134   b  for selective operation thereof. In some exemplary embodiments, the electromechanical actuator  522  may include an electric motor (not shown) coupled to a screw drive (not shown), solenoids (not shown), linear induction motors (not shown), and/or other electrically operable linear actuators recognized in the art. The electromechanical actuator  522  is operable to move a piston  524  in the directions of arrows A 16  and A 17 . Thus, a channel  524   a  defined through the piston  524  may be moved into and out of alignment with a fluid passage  526  coupled energy reservoir  506  and the fluid conduit  514  extending to the corrosion chamber  510  ( FIG. 27 ). In some embodiments, the chemical solution “C” is pressurized within the energy reservoir  506  such that an internal pressure drives the chemical solution “C” through the fluid conduit  514  and into the corrosion chamber  510  ( FIG. 27 ) in response to movement of the channel  524   a  into alignment with the fluid passage  526  and the fluid conduit  514 . In some exemplary embodiments, the movement of the chemical solution “C” through the fluid conduit  514  may be assisted by the electric pump  512  ( FIG. 27 ). 
     As illustrated in  FIG. 29B , in some exemplary embodiments, the remotely actuated valve  520   b  may comprise a hydraulic actuator  530  operable to urge the piston  524  in the direction of arrow A 16 . In some exemplary embodiments, the hydraulic actuator  530  may comprise a fluidic connection to a source of hydraulic fluid “H” such as drilling mud  36  flowing through the drill string  18  ( FIG. 1 ) and/or the annulus  40  ( FIG. 1 ). The hydraulic fluid “H” may be in direct contact with the piston  524 , or may be operably coupled thereto through an intermediate mechanism (not shown). In some exemplary embodiments, a biasing member  532  is provided to urge the piston  524  in the direction of arrow A 17 . The biasing member  532  may comprise a compression spring, a stack of spring washers or other mechanisms recognized in the art. 
     A biasing force provided by the biasing member  532  defines the hydraulic pressure required for the hydraulic actuator  530  to move the piston  524  sufficiently in the direction of arrow A 16  to an aligned position, e.g., a position with the channel  524   a  aligned with the fluid passage  526  and the fluid conduit  514  in which the chemical solution “C” may be released from the energy reservoir  506 . Since the pressure of the drilling mud  36  may generally be a function of the depth of the wellbore  12  ( FIG. 1 ), the biasing force provided by biasing member  532  may be selected to induce movement of the piston  524  to the aligned position at a predetermined depth in the wellbore  12  ( FIG. 1 ). Thus, the hydraulic actuator  530  may be operable to passively provide the chemical solution “C” to the corrosion chamber  510  ( FIG. 27 ) thereby inducing failure of the support member  504  ( FIG. 27 ) and effecting an adjustment of the bend angle θ. For example, delivery of the hydraulic actuator  530  to a predetermined depth in the wellbore  12  ( FIG. 1 ) may induce the adjustment in the bend angle θ with no further instruction from an operator. 
     In some exemplary embodiments, the hydraulic actuator  530  may additionally or alternatively comprise a single or dual action hydraulic cylinder (not shown) coupled to communication unit  134   a  and controller  134   b  for selective movement of the piston  524  in the direction of arrows A 16  and A 17 . Thus, the hydraulic actuator  530  may be actively controlled by an operator at the surface location “S” ( FIG. 1 ). 
     As illustrated in  FIG. 29C , in some exemplary embodiments, the remotely actuated valve  520   c  may comprise a thermal actuator  536 . The thermal actuator  536  comprises a thermal expansion chamber  538  that is sealed or fluidly isolated within the annular member  102 . The thermal expansion chamber  538  may be charged or filled with a compressible and generally inert fluid. In some embodiments, the fluid can be a liquid such as water, and in some embodiments the fluid may be a gas such as such as gaseous argon or nitrogen “N.” The nitrogen “N” or other compressible fluid will expand when heated to move the piston  524  in the direction of arrow A 16  against the bias of the biasing member  532 . As described above, movement of the piston  524  into alignment with the fluid passage  526  and the fluid conduit  514  releases the chemical solution “C” to the corrosion chamber  510  ( FIG. 27 ). The nitrogen “N” or other compressible fluid may be passively heated by the down-hole environment, and/or may optionally be actively heated by a heater  540 . The heater  540  may comprise an electric resistance heater operably coupled to the communication unit  134   a  and controller  134   b  for selective activation thereof. 
     Referring to  FIGS. 30A through 30C , the energy delivery system  502  may include a remotely actuated valve  542   a ,  542   b ,  542   c  operable to release the chemical solution “C” from the energy reservoir  506 . The remotely actuated valves  542   a ,  542   b ,  542   c  each include a diaphragm  544  that may be selectively ruptured with a rupturing tool  546 . The diaphragm  544  defines a boundary of the energy reservoir  506  and maintains the fluid within the energy reservoir  506 . Rupturing the diaphragm  544  releases the chemical solution “C” into a rupture chamber  548 , which is in fluid communication with the corrosion chamber  510  ( FIG. 27 ) through fluid conduit  514 . Thus, the chemical solution “C” may be selectively provided to the corrosion chamber  510  ( FIG. 27 ) by rupturing the diaphragm  544 . In some exemplary embodiments, the rupturing tool  546  may be a pin, needle or knife that is selectively movable in the direction of arrow A 18  toward the diaphragm  544 . 
     In some exemplary embodiments, the rupturing tool  546  may be operatively coupled to any of the types of actuators described above for moving the piston  524  ( FIGS. 29A through 29C ). For example the rupturing tool  546  may be operatively coupled to an electromechanical actuator  550  ( FIG. 30A ), which may comprise a solenoid  552  coupled to the communication unit  134   a  and controller  134   b  for selectively moving the rupturing tool  546  in the direction of arrow A 18 . In some other exemplary embodiments, a hydraulic actuator  554  ( FIG. 30B ) may be provided that is operable to move a piston  558  and the rupturing tool  546  together. The piston  558  may be exposed to a hydraulic fluid “H” such as drilling mud  36  to urge rupturing tool  546  in the direction of arrow A 18 . As illustrated in  FIG. 30C , a thermal actuator  560  may include a thermal expansion chamber  562  charged with a compressible fluid such a nitrogen “N.” A piston  564  may be responsive to temperature increases of the nitrogen “N” to move the piston  558  and rupturing tool  546  in the direction of arrow A 18 . 
     Referring to  FIGS. 31A and 31B , energy delivery system  570  directs energy from the internal passageway  104  to a support member  120  to facilitate an adjustment to the bend angle θ. The energy delivery system  570  includes a radial flow passage  572  extending through a sidewall of the annular member  102 . The radial flow passage  572  is a fluid conduit extending between the internal passageway  104  and an exterior of the annular member  102  between the upper and lower flanges  116 ,  118 . In some exemplary embodiments, an axis X 5  of the radial flow passage  572  intersects a longitudinal axis X 6  of the support member  120 . Drilling mud  36  and/or chemical solution “C” may be diverted from the internal passageway  104  through the radial flow passage  572  to accelerate erosion and corrosion support member  120 . Generally in drilling operations, an internal pressure within the internal passageway  104  will be greater than an external pressure of the annular member  102 . The energy associated with the higher pressure on fluids  36 , “C” within the internal passageway  104  may be delivered to the support member  102  to abrasively erode the support member  102  or to accelerate corrosion thereof. An exit  574  of the radial flow passage  572  may include a nozzle or other flow control tool, which focuses the fluidic energy on the targeted support member  120 . 
     An initiation valve  578  may be provided within the radial flow passage  572  to obstruct fluid flow through the radial flow passage  572  until an adjustment of the bend angle θ is to be made. In some embodiments, the initiation valve  578  may include an electronically operable valve coupled to the communication unit  134  and controller  134   b  such that the initiation valve  578  is responsive to an instruction signal to selectively permit and restrict fluid flow through the radial flow passage  572 . In some exemplary embodiments, the initiation valve  578  may be a rupture disk responsive to an increase in pressure within the internal passageway  104 . Thus, temporarily increasing the pressure within the internal passageway  104 , e.g., using mud pump  38  ( FIG. 1 ), may serve to rupture the rupture disk, and thereby divert drilling mud  36  and/or chemical solution “C” through the radial flow passage  572 . 
     Referring to  FIG. 31B , with continued reference to  FIG. 31A , in some exemplary embodiments, a check valve  580  may be provided within the radial flow passage  572 . The check valve  580  may include a biasing member  582  that maintains a piston  584  in a seated position within the radial flow passage  572 . When an adjustment to the bend angle θ is to be made, the pressure of drilling mud  36  or chemical solution “C” may be increased within the internal passageway  104 . The pressure may be increased, e.g., by operating the mud pump  38  ( FIG. 1 ) at an increased capacity. The increased pressure in the internal passageway  104  counteracts a biasing force of the biasing member  582 , and moves the piston  584  in the direction of arrow A 19 . The piston  584  moves to an unseated position, e.g., away from valve seat  586 , thereby permitting fluid flow through the radial flow passage  572 . Erosion and/or corrosion of the support member  120  may then be facilitated by the drilling mud  36  or chemical solution “C” until the support member  102  fails, and the bend angle θ is adjusted. Once the support member  120  fails, the mud pumps  38  ( FIG. 1 ) may be operated at lower or nominal capacity to decrease the pressure in the internal passageway  104 , and return the piston  584  to the seated position under the bias of the biasing member  582 . Thus, the mud pumps  38  ( FIG. 1 ) may again operate at a nominal capacity once the support member  120  has failed, thereby permitting continued drilling under nominal operational characteristics with the bottom hole assembly  20  ( FIG. 2 ). 
     Directional Drilling with Adjustable Bent Housings 
     Referring to  FIGS. 32A through 32C , the drill string  18  may be deployed in main wellbore  602  to form a branch wellbore  604  extending laterally therefrom. Drilling operations often include forming branch or lateral wellbores, and one difficulty in these operations encouraging a BHA  20  to extend from the main wellbore  602  at the correct location to drill the branch wellbore  604 . To facilitate initiating the branch wellbore  604  at the correct location, a casing  606  having a window  608  formed therein is provided in the main wellbore  602 . In some embodiments, the casing  606  is secured within the geologic formation “F” by an annular cement layer  610 . The window  608  may be difficult to locate with conventional drilling equipment. However, a BHA  20  including any one of the adjustable drill string housings described herein may facilitate locating the window  608 . For example, with an adjustable drill string housing, the BHA  20  may be run into the main wellbore with a relatively large or steep bend angle θ to facilitate locating the window  608 , and thereafter, the bend angle θ may be reduced to relieve internal stresses in the BHA  20  and improve the reliability of the drilling operations. 
     The BHA  20  may be run into the main wellbore  602  on drill string  18 . In some exemplary embodiments, the BHA  20  may be run into the main wellbore  602  while a lateral separation is maintained between the drill bit  14  and the casing  606 , and when the BHA  20  is approaches the window  608  ( FIG. 32A ) an adjustment can be made to induce lateral contact between the drill bit  14  and the casing  606 . For example, in some embodiments, the BHA  20  may be positioned at a location up-hole of the widow  608  when an adjustment mechanism, e.g., the adjustment mechanism  110  described above with reference to  FIG. 4 , may be employed to increase the bend angle θ until the drill bit  14  contacts the casing  606 . In some exemplary embodiments, the bend angle θ may be increased by transmitting an instruction signal to the communication unit  134   a  ( FIG. 4 ) that may be recognized by the controller  134   b  ( FIG. 4 ). In response to receiving the instruction signal, the controller  134   b  may initiate a predetermined sequence of instructions stored thereon which cause the electric motor  124  ( FIG. 4 ) to operate and thereby adjust an internal stress in support member  120  as described above. The change in the internal stress in the support member  120  may induce the bend angle θ to adjust until the drill bit  14  laterally contacts the casing  208 . In some embodiments, the internal stresses imparted to the support member  120  induce elastic deformation such that internal stresses are reversible. In some embodiments, an actuator other than the electric motor  124  ( FIG. 4 ) may be responsive to the instruction signal to induce the change in the internal stresses of the support member  120 . For example, the actuator may include a hydraulically actuated piston  166  ( FIG. 8 ), and/or a thermally actuated sleeve  120   e ″ ( FIG. 11 ). In some embodiments, an exterior-angle radial side of the annular member  102  may also contact an opposite side of the casing  606 . 
     An operator at the surface location “S” ( FIG. 1 ) may confirm that the drill bit  14  is in contact with the casing by  606  by moving the drill string  18 , e.g., along longitudinal axis X 7  of the main wellbore  602 . The operator may detect an increased resistance to axial motion due to the frictional contact between the drill bit  14  and the casing  606 . In some other embodiments, the operator may determine that the drill bit  14  is in contact with the casing  606  by monitoring a measurement mechanism, e.g., measurement mechanism  138  ( FIG. 5 ). For example, the measurement mechanism  138  ( FIG. 5 ) may be queried until a predetermined bend angle θ is detected. 
     In some exemplary embodiments, the BHA  20  may be run into the main wellbore  602  with the drill bit  14  in lateral contact with the casing  606 . For example, annular member  102  may be provided in a pre-stressed configuration maintained by a sacrificial support member  120 , and the sacrificial support member  120  may maintain a bend angle θ that sufficiently large to cause the lateral contact. 
     With the drill bit  14  in contact with casing  606 , the drill string  18  may be advanced into the main wellbore  602  in the direction of arrow A 20 . In some embodiments, the drill string  18  may also be rotated, e.g., about axis X 7  to facilitate locating the window  608 . When the drill string  18  reaches the window  608  ( FIG. 32B ), the drill bit  14  may deflect laterally into the window  608 , thereby relieving the lateral contact between the drill bit  14  and the casing  606 . The deflection of the drill bit  14  into the window  608  facilitates detection of the window  608  from the surface location “S.” The relief of the lateral contact can be detected since, e.g., the resistance to axial motion will decrease, and in some embodiments, the bend angle θ may change when the drill sting  18  is no longer laterally constrained within the casing  606 . The operator may expediently detect these changes to confirm that the window  608  has been reached, and that the drill bit  14  is in position for drilling the branch wellbore  604 . 
     With the drill bit  14  within the window  608 , the operator may initiate an alteration of the bend angle θ to define a direction of the branch wellbore  604 . The operator may alter the bend angle θ prior to commencing drilling the branch wellbore  604 , or in some embodiments, may commence drilling the branch wellbore before the bend angle θ is fully altered. The bend angle θ may be reduced to relieve internal stresses within the BHA  20  and reduce the risk of down-hole failure. In some exemplary embodiments, the adjustment mechanism  110  ( FIG. 4 ) may be employed to adjust the bend angle θ by operating electric motor  124  ( FIG. 4 ) as described above. In some embodiments, the galvanic corrosion system  330  ( FIG. 16A ) and/or energy delivery system  502  may be employed to induce a failure in the support member  120  to thereby adjust bend angle θ. In some exemplary embodiments, the support member  120  may be induced to corrode in a drilling fluid such as drilling mud  36  ( FIG. 1 ) and/or a chemical solution “C” conveyed through the drill string  18  to commence rotation of the drill bit  14  and drilling of the branch wellbore  604 . In some exemplary embodiments, the bend angle θ may be altered by inducing failure of the support member  120  by providing an electric current to the support member  120  to accelerate galvanic corrosion of the support member  120 . The bend angle θ may be altered down-hole, with the drill bit  14  extending into or through the window  608 , using any of the methods and mechanisms described above. 
     In some exemplary embodiments, the adjustment to the bend angle θ may be verified, e.g., by querying a measurement mechanism  138 ,  148  ( FIGS. 5 and 6 ), and the branch wellbore  604  ( FIG. 32C ) may be drilled. The drill bit  14  may be turned relative to the drill string  18  by employing power unit  50  ( FIG. 2 ), and the branch wellbore  604 . The branch wellbore  604  extends laterally from the main wellbore  602 . It will be appreciated that in some embodiments, the main wellbore  602  may not extend to a surface location “S” ( FIG. 1 ), but may branch from another wellbore (not shown). 
     In one aspect of the disclosure, an adjustable drill string housing includes an annular member and an adjustment mechanism. The annular member has an upper end and a lower end, and defines an upper longitudinal axis extending through the upper end and a lower longitudinal axis extending through the lower end. The annular member is deformable about a bend axis between a first configuration wherein the upper and lower longitudinal axes are disposed at a first bend angle with respect to one another and a second configuration wherein the upper and lower longitudinal axes are disposed at a second bend angle with respect to one another. The adjustment mechanism includes at least one support member carried by the annular member radially offset from the upper and lower longitudinal axes and extending across the bend axis. The adjustment mechanism is selectively movable between a first arrangement for maintaining the annular member in the first configuration and a second arrangement for maintaining the annular member in the second configuration. The adjustment mechanism changes an internal stress in the at least one support member to move between the first and second arrangements. 
     In some exemplary embodiments, the adjustment mechanism further includes an actuator operably coupled to the at least one support member for selectively changing the internal stress in the at least one support member. The actuator may be communicatively coupled to a communication unit, and the actuator may be responsive to instruction signals received by the communication unit. In some exemplary embodiments, the drill string housing further includes a feedback device operable to provide a signal from which the bend angle is determinable to the communication unit, wherein the communication unit is operable to provide a confirmation signal indicative of a successful adjustment of the bend angle. In some embodiments, feedback device may be operably coupled to the at least one support member to detect a change in a longitudinal length of the at least one support member. 
     In one or more exemplary embodiments, the actuator comprises a motor operably coupled to a torque nut for imparting internal stresses to the at least one support member. The torque nut may be supported on the annular member such that movement of the at least one support member in a first direction with respect to the torque nut increases the internal stresses in the at least one support member and movement of the at least one support member in a second direction decreases the internal stresses in the at least one support member. 
     In some exemplary embodiments, the actuator includes a thermal actuator responsive to temperature changes to change the internal stresses in the at least one support member. The at least one support member may include at least one of a shape memory alloy operable to change shape responsive to at least a threshold temperature change and an outer expansion sleeve having a coefficient of thermal expansion greater than that of the annular member. In one or more exemplary embodiments, the actuator may include a hydraulic actuator having a piston movable in response to the displacement of hydraulic fluid, and the piston may be operably coupled to the at least one support member for selectively changing the internal stress in the at least one support member. 
     In some exemplary embodiments, the adjustable drill string housing may further include upper and lower flanges extending radially from the annular member, and at least one support member may be supported by the upper and lower flanges. The annular member may define an initial bend angle in an unstressed state such that the annular member defines an interior-angle radial side and an exterior-angle radial side. The at least one support member may include at least one interior-angle support member disposed on the interior-angle radial side of the annular member and at least one exterior-angle support member disposed on the exterior-angle radial side of the annular member. 
     In another aspect, the present disclosure is directed to a method of forming and operating an adjustable drill string housing. The method includes (a) manufacturing an annular member defining an initial bend angle therein about a bend axis, the bend angle defined between upper and lower longitudinal axes extending through respective upper and lower ends of the annular member, (b) installing at least one support member on the annular member such that the at least one support member is radially offset from the upper and lower longitudinal axes and extends across the bend axis, and (c) pre-stressing the at least one support member move the annular member to a first configuration wherein the upper and lower longitudinal axes are disposed at a bend angle different from the initial bend angle. 
     In some exemplary embodiments, pre-stressing the at least one support member includes imparting a compressive force to a first support, member of the at least one support, member and imparting a tensile force to a second support member of the at least one support member. In some exemplary embodiments, the method may further include (d) deploying the adjustable drill string housing into a wellbore in the first configuration, and (e) triggering, with the adjustable drill string housing in the wellbore, a change in an internal stress in the at least one support member to thereby bend the annular member from the first configuration to a second configuration within the wellbore. 
     In another aspect, the present disclosure is directed to a method of forming a wellbore include (a) defining a planned well profile for the wellbore, (b) initiating drilling along the planned well profile with a drill string, (c) determining that an adjustment to a bend angle defined in an annular member interconnected in the drill string would facilitate following the planned well profile, and (d) triggering a change in an internal stress of at least one support member carried by the annular member and extending across a bend axis of the annular member to thereby bend the annular member from a first configuration to a second configuration. 
     In some exemplary embodiments, triggering the change in the at least one support member includes imparting a compressive force to a first support member of the at least one support member and imparting a tensile force to a second support member of the at least one support member. In some exemplary embodiments, the method further includes (e) querying a measurement mechanism operably coupled to the annular member to verify a change in the bend angle, and (f) further comprising determining a radial orientation of the annular member in the wellbore, and selecting the radial support member in which to trigger the change in the internal stress from a plurality of support members radially spaced around the annular member. In some exemplary embodiments, determining the radial orientation of the annular member in the wellbore, selecting the radial support member, and changing the internal stress in the selected support members may be performed as the annular member is in motion in a radial progression. In some embodiments, constant and real time adjustments may be made to the bend angle in this manner to maintain a bias to bend in a desired direction. 
     Moreover, any of the methods described herein may be embodied within a system including electronic processing circuitry to implement any of the methods, or a in a computer-program product including instructions which, when executed by at least one processor, causes the processor to perform any of the methods described herein. 
     The Abstract of the disclosure is solely for providing the United States Patent and Trademark Office and the public at large with a way by which to determine quickly from a cursory reading the nature and gist of technical disclosure, and it represents solely one or more embodiments. 
     While various embodiments have been illustrated in detail, the disclosure is not limited to the embodiments shown. Modifications and adaptations of the above embodiments may occur to those skilled in the art. Such modifications and adaptations are in the spirit and scope of the disclosure.