Abstract:
An expandable downhole tool comprises a tubular body having an axial flowbore extending therethrough, at least one moveable arm, and a selectively actuatable sleeve that prevents or allows the at least one moveable arm to translate between a collapsed position and an expanded position. A method of expanding a downhole tool comprises disposing the downhole tool comprising at least one moveable arm within the wellbore, biasing the at least one moveable arm to a collapsed position corresponding to an initial diameter of the downhole tool, flowing a fluid through an axial flowbore extending through the downhole tool while preventing the fluid from communicating with a different flowpath of the downhole tool, allowing the fluid to communicate with the different flowpath by introducing an actuator into the wellbore, and causing the at least one moveable arm to translate to an expanded position corresponding to an expanded diameter of the downhole tool.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This is a continuation application of co-pending U.S. application Ser. No. 10/841,314 filed May 7, 2004 and entitled “Expandable Underreamer/Stabilizer”, which is a divisional application of U.S. Patent No.  6 , 732 , 817  issued May  11 ,  2004  and entitled “Expandable Underreamer/Stabilizer”, both hereby incorporated herein by reference for all purposes. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable.  
       REFERENCE TO A MICROFICHE APPENDIX  
       [0003]     Not applicable.  
       FIELD OF THE INVENTION  
       [0004]     The present disclosure relates generally to underreamers for enlarging a borehole below a restriction to result in a borehole that is larger than the restriction. The present disclosure also relates generally to stabilizers for stabilizing a drilling assembly within an underreamed portion of borehole. More particularly, the present disclosure relates to a selectively actuatable, expandable downhole tool that may function as an underreamer, or as a stabilizer, or as a combination thereof.  
       BACKGROUND  
       [0005]     In the drilling of oil and gas wells, concentric casing strings are installed and cemented in the borehole as drilling progresses to increasing depths. Each new casing string is supported within the previously installed casing string, thereby limiting the annular area available for the cementing operation. Further, as successively smaller diameter casing strings are suspended, the flow area for the production of oil and gas is reduced. Therefore, to increase the annular space for the cementing operation, and to increase the production flow area, it is often desirable to enlarge the borehole below the terminal end of the previously cased borehole. By enlarging the borehole, a larger annular area is provided for subsequently installing and cementing a larger casing string than would have been possible otherwise. Accordingly, by enlarging the borehole below the previously cased borehole, the bottom of the formation can be reached with comparatively larger diameter casing, thereby providing more flow area for the production of oil and gas.  
         [0006]     Various methods have been devised for passing a drilling assembly through an existing cased borehole and enlarging the borehole below the casing. One such method is the use of an underreamer, which has basically two operative states—a closed or collapsed state, where the diameter of the tool is sufficiently small to allow the tool to pass through the existing cased borehole, and an open or partly expanded state, where one or more arms with cutters on the ends thereof extend from the body of the tool. In this latter position, the underreamer enlarges the borehole diameter as the tool is rotated and lowered in the borehole.  
         [0007]     A “drilling type” underreamer is typically used in conjunction with a conventional pilot drill bit positioned below or downstream of the underreamer. The pilot bit can drill the borehole at the same time as the underreamer enlarges the borehole formed by the bit. Underreamers of this type usually have hinged arms with roller cone cutters attached thereto. Most of the prior art underreamers utilize swing out cutter arms that are pivoted at an end opposite the cutting end of the cutting arms, and the cutter arms are actuated by mechanical or hydraulic forces acting on the arms to extend or retract them. Typical examples of these types of underreamers are found in U.S. Pat. Nos. 3,224,507; 3,425,500 and 4,055,226. In some designs, these pivoted arms tend to break during the drilling operation and must be removed or “fished” out of the borehole before the drilling operation can continue. The traditional underreamer tool typically has rotary cutter pocket recesses formed in the body for storing the retracted arms and roller cone cutters when the tool is in a closed state. The pocket recesses form large cavities in the underreamer body, which requires the removal of the structural metal forming the body, thereby compromising the strength and the hydraulic capacity of the underreamer. Accordingly, these prior art underreamers may not be capable of underreaming harder rock formations, or may have unacceptably slow rates of penetration, and they are not optimized for the high fluid flow rates required. The pocket recesses also tend to fill with debris from the drilling operation, which hinders collapsing of the arms. If the arms do not fully collapse, the drill string may easily hang up in the borehole when an attempt is made to remove the string from the borehole.  
         [0008]     Conventional underreamers have several disadvantages, including cutting structures that are typically formed of sections of drill bits rather than being specifically designed for the underreaming function. Therefore, the cutting structures of most underreamers do not reliably underream the borehole to the desired diameter. A further disadvantage is that adjusting the expanded diameter of a conventional underreamer requires replacement of the cutting arms with larger or smaller arms, or replacement of other components of the underreamer tool. It may even be necessary to replace the underreamer altogether with one that provides a different expanded diameter. Another disadvantage is that many underreamers are designed to automatically expand when drilling fluid is pumped through the drill string, and no indication is provided at the surface that the underreamer is in the fully-expanded position. In some applications, it may be desirable for the operator to control when the underreamer expands.  
         [0009]     Accordingly, it would be advantageous to provide an underreamer that is stronger than prior art underreamers, with a hydraulic capacity that is optimized for the high flowrate drilling environment. It would further be advantageous for such an underreamer to include several design features, namely cutting structures designed for the underreaming function, mechanisms for adjustment of the expanded diameter without requiring component changes, and the ability to provide indication at the surface when the underreamer is in the fully-expanded position. Moreover, in the presence of hydraulic pressure in the drill string, it would be advantageous to provide an underreamer that is selectively expandable.  
         [0010]     Another method for enlarging a borehole below a previously cased borehole section includes using a winged reamer behind a conventional drill bit. In such an assembly, a conventional pilot drill bit is disposed at the lowermost end of the drilling assembly with a winged reamer disposed at some distance behind the drill bit. The winged reamer generally comprises a tubular body with one or more longitudinally extending “wings” or blades projecting radially outwardly from the tubular body. Once the winged reamer has passed through any cased portions of the wellbore, the pilot bit rotates about the centerline of the drilling axis to drill a lower borehole on center in the desired trajectory of the well path, while the eccentric winged reamer follows the pilot bit and engages the formation to enlarge the pilot borehole to the desired diameter.  
         [0011]     Yet another method for enlarging a borehole below a previously cased borehole section includes using a bi-center bit, which is a one-piece drilling structure that provides a combination underreamer and pilot bit. The pilot bit is disposed on the lowermost end of the drilling assembly, and the eccentric underreamer bit is disposed slightly above the pilot bit. Once the bi-center bit has passed through any cased portions of the wellbore, the pilot bit rotates about the centerline of the drilling axis and drills a pilot borehole on center in the desired trajectory of the well path, while the eccentric underreamer bit follows the pilot bit and engages the formation to enlarge the pilot borehole to the desired diameter. The diameter of the pilot bit is made as large as possible for stability while still being capable of passing through the cased borehole. Examples of bi-center bits may be found in U.S. Pat. Nos. 6,039,131 and 6,269,893.  
         [0012]     As described above, winged reamers and bi-center bits each include underreamer portions that are eccentric. A number of disadvantages are associated with this design. First, before drilling can continue, cement and float equipment at the bottom of the lowermost casing string must be drilled out. However, the pass-through diameter of the drilling assembly at the eccentric underreamer portion barely fits within the lowermost casing string. Therefore, off-center drilling is required to drill out the cement and float equipment to ensure that the eccentric underreamer portions do not damage the casing. Accordingly, it is desirable to provide an underreamer that collapses while the drilling assembly is in the casing and that expands to underream the previously drilled borehole to the desired diameter below the casing.  
         [0013]     Further, due to directional tendency problems, these eccentric underreamer portions have difficulty reliably underreaming the borehole to the desired diameter. With respect to a bi-center bit, the eccentric underreamer bit tends to cause the pilot bit to wobble and undesirably deviate off center, thereby pushing the pilot bit away from the preferred trajectory of drilling the well path. A similar problem is experienced with respect to winged reamers, which only underream the borehole to the desired diameter if the pilot bit remains centralized in the borehole during drilling. Accordingly, it is desirable to provide an underreamer that remains concentrically disposed in the borehole while underreaming the previously drilled borehole to the desired diameter.  
         [0014]     In drilling operations, it is conventional to employ a tool known as a “stabilizer.” In standard boreholes, traditional stabilizers are located in the drilling assembly behind the drill bit for controlling the trajectory of the drill bit as drilling progresses. Traditional stabilizers control drilling in a desired direction, whether the direction is along a straight borehole or a deviated borehole.  
         [0015]     In a conventional rotary drilling assembly, a drill bit may be mounted onto a lower stabilizer, which is disposed approximately 5 feet above the bit. Typically the lower stabilizer is a fixed blade stabilizer that includes a plurality of concentric blades extending radially outwardly and spaced azimuthally around the circumference of the stabilizer housing. The outer edges of the blades are adapted to contact the wall of the existing cased borehole, thereby defining the maximum stabilizer diameter that will pass through the casing. A plurality of drill collars extends between the lower stabilizer and other stabilizers in the drilling assembly. An upper stabilizer is typically positioned in the drill string approximately 30-60 feet above the lower stabilizer. There could also be additional stabilizers above the upper stabilizer. The upper stabilizer may be either a fixed blade stabilizer or, more recently, an adjustable blade stabilizer that allows the blades to be collapsed into the housing as the drilling assembly passes through the casing and then expanded in the borehole below. One type of adjustable concentric stabilizer is manufactured by Andergauge U.S.A., Inc., Spring, Tex. and is described in U.S. Pat. No. 4,848,490. Another type of adjustable concentric stabilizer is manufactured by Halliburton, Houston, Texas and is described in U.S. Pat. Nos. 5,318,137; 5,318,138; and 5,332,048.  
         [0016]     In operation, if only the lower stabilizer was provided, a “fulcrum” type assembly would be present because the lower stabilizer acts as a fulcrum or pivot point for the bit. Namely, as drilling progresses in a deviated borehole, for example, the weight of the drill collars behind the lower stabilizer forces the stabilizer to push against the lower side of the borehole, thereby creating a fulcrum or pivot point for the drill bit. Accordingly, the drill bit tends to be lifted upwardly at an angle, i.e. build angle. Therefore, a second stabilizer is provided to offset the fulcrum effect. Namely, as the drill bit builds angle due to the fulcrum effect created by the lower stabilizer, the upper stabilizer engages the lower side of the borehole, thereby causing the longitudinal axis of the bit to pivot downwardly so as to drop angle. A radial change of the blades of the upper stabilizer can control the pivoting of the bit on the lower stabilizer, thereby providing a two-dimensional, gravity based steerable system to control the build or drop angle of the drilled borehole as desired.  
         [0017]     When an underreamer or a winged reamer tool is operating behind a conventional bit to underream the borehole, that tool provides the same fulcrum effect to the bit as the lower stabilizer in a standard borehole. Similarly, when underreaming a borehole with a bi-center bit, the eccentric underreamer bit provides the same fulcrum effect as the lower stabilizer in a standard borehole. Accordingly, in a drilling assembly employing an underreamer, winged reamer, or a bi-center bit, a lower stabilizer is not typically provided. However, to offset the fulcrum effect imparted by to the drill bit, it would be advantageous to provide an upper stabilizer capable of controlling the inclination of the drilling assembly in the underreamed section of borehole.  
         [0018]     In particular, it would be advantageous to provide an upper stabilizer that engages the wall of the underreamed borehole to keep the centerline of the pilot bit centered within the borehole. When utilized with an eccentric underreamer that tends to force the pilot bit off center, the stabilizer blades would preferably engage the opposite side of the expanded borehole to counter that force and keep the pilot bit on center.  
       SUMMARY OF THE INVENTION  
       [0019]     In various embodiments, a downhole expandable tool may be used as an underreamer to enlarge the diameter of a borehole below a restriction, or may be used as a stabilizer to control the directional tendencies of a drilling assembly in an underreamed borehole.  
         [0020]     In one aspect, the present disclosure relates to an expandable downhole tool for use within a wellbore comprising a tubular body having an axial flowbore extending therethrough, at least one moveable arm, and a selectively actuatable sleeve that prevents or allows the at least one moveable arm to translate between a collapsed position and an expanded position. In various embodiments, the tool further comprises, a structure for adjusting the expanded position, at least one nozzle that translates with the at least one moveable arm, a spring to bias the at least one moveable arm to the collapsed position, at least one axial recess for storing the at least one moveable arm in the collapsed position, or a piston that translates the at least one moveable arm from the collapsed position to the expanded position. In an embodiment, the at least one moveable arm comprises a plurality of moveable arms spaced apart circumferentially around the tool body.  
         [0021]     The at least one moveable arm may engage the wellbore in the expanded position, and in various embodiments, the at least one moveable arm may include at least one set of cutting structures for underreaming the wellbore in the expanded position, or at least one wear structure for stabilizing the drilling assembly within the wellbore. In various embodiments, the at least one moveable arm may provide back reaming capability or gauge protection capability. The at least one moveable arm may also translate axially and radially.  
         [0022]     In an embodiment, the sleeve is biased to a first position that prevents fluid communication between a chamber and the flowbore, and the at least one moveable arm may be prevented from translating between the collapsed position and the expanded position when the sleeve is biased to the first position. The sleeve may be selectively actuatable to a second position that allows fluid communication between the chamber and the flowbore, and the at least one moveable arm may be translatable between the collapsed position and the expanded position when the sleeve is in the second position. In an embodiment, the tool further includes an actuator for selectively actuating the sleeve.  
         [0023]     The body may comprise a plurality of angled channels, and in an embodiment, the at least one moveable arm comprises a plurality of extensions corresponding to and engaging the plurality of angled channels. The tool may further comprise at least one borehole engaging pad comprising wear structures.  
         [0024]     In another aspect, the present disclosure relates to a method of expanding a downhole tool within a wellbore comprising disposing the downhole tool comprising at least one moveable arm within the wellbore, biasing the at least one moveable arm to a collapsed position corresponding to an initial diameter of the downhole tool, flowing a fluid through an axial flowbore extending through the downhole tool while preventing the fluid from communicating with a different flowpath of the downhole tool, allowing the fluid to communicate with the different flowpath by introducing an actuator into the wellbore, and causing the at least one moveable arm to translate to an expanded position corresponding to an expanded diameter of the downhole tool. In various embodiments, the method further comprises underreaming the wellbore in the expanded position, or stabilizing a drilling assembly connected to the downhole tool in the expanded position. The different flowpath may comprise a chamber in communication with a piston engaging the at least one moveable arm; and translating the at least one moveable arm to the expanded position may comprise translating the piston when the fluid communicates with the chamber. In an embodiment, the method further comprises adjusting the expanded diameter.  
         [0025]     In yet another aspect, the present disclosure relates to an expandable downhole tool for use within a wellbore comprising a tubular body, and at least one moveable arm, wherein the expandable downhole tool is selectively actuatable to allow or prevent the at least one moveable arm to translate between a collapsed position and an expanded position in response to a fluid flowing through the tubular body.  
         [0026]     Thus, the present invention comprises a combination of features and advantages that enable it to overcome various problems of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein:  
         [0028]      FIG. 1  is a schematic, cross-sectional view of an exemplary drilling assembly that employs one embodiment of the invention and that includes a conventional drill bit drilling a borehole within a formation, an underreamer enlarging the borehole above the bit, and a stabilizer above the underreamer controlling the directional tendencies of the drilling assembly in the underreamed borehole;  
         [0029]      FIG. 2  is a schematic, cross-sectional view of another exemplary drilling assembly that employs one embodiment of the invention and that includes a conventional drill bit drilling a borehole within a formation, a winged reamer enlarging the borehole above the bit, and a stabilizer above the winged reamer controlling the directional tendencies of the drilling assembly in the underreamed borehole;  
         [0030]      FIG. 3  is a schematic, cross-sectional view of still another exemplary drilling assembly that employs one embodiment of the invention and that includes a bi-center bit drilling and enlarging a borehole within a formation, and a stabilizer above the bi-center bit controlling the directional tendencies of the drilling assembly in the underreamed borehole;  
         [0031]      FIG. 4  is a cross-sectional elevation view of one embodiment of the expandable tool of the present invention, showing the moveable arms in the collapsed position;  
         [0032]      FIG. 5  is a cross-sectional elevation view of the expandable tool of  FIG. 4 , showing the moveable arms in the expanded position;  
         [0033]      FIG. 6  is a perspective view of a “blank” arm for the expandable tool of  FIG. 4 ;  
         [0034]      FIG. 7  is a top view of an exemplary arm for the expandable tool of  FIG. 4  including a wear pad and cutting structures for back reaming and underreaming;  
         [0035]      FIG. 8  is a side elevation view of the arm of  FIG. 7 ;  
         [0036]      FIG. 9  is a perspective view of the arm of  FIG. 7 ;  
         [0037]      FIG. 10  is a perspective view of the drive ring of the expandable tool of  FIG. 4 ;  
         [0038]      FIG. 11  is a cross-sectional elevation view of an alternative embodiment of the expandable tool of the present invention, showing the moveable arms in the collapsed position; and  
         [0039]      FIG. 12  is a cross-sectional elevation view of the alternative embodiment of  FIG. 11 , showing the moveable arms in the expanded position. 
     
    
     NOTATION AND NOMENCLATURE  
       [0040]     Certain terms are used throughout the following description and claims to refer to particular assembly components. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ”.  
       DETAILED DESCRIPTION  
       [0041]     The present invention relates to methods and apparatus for underreaming to enlarge a borehole below a restriction, such as casing. Alternatively, the present invention relates to methods and apparatus for stabilizing a drilling assembly and thereby controlling the directional tendencies of the drilling assembly within an enlarged borehole. The present invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present invention with the understanding that the disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein.  
         [0042]     In particular, various embodiments of the present invention provide a number of different constructions and methods of operation. Each of the various embodiments of the present invention may be used to enlarge a borehole, or to provide stabilization in a previously enlarged borehole, or in a borehole that is simultaneously being enlarged. The preferred embodiments of the expandable tool of the present invention may be utilized as an underreamer, or as a stabilizer behind a bi-center bit, or as a stabilizer behind a winged reamer or underreamer following a conventional bit. The embodiments of the present invention also provide a plurality of methods for use in a drilling assembly. It is to be fully recognized that the different teachings of the embodiments disclosed herein may be employed separately or in any suitable combination to produce desired results.  
         [0043]     It should be appreciated that the expandable tool described with respect to the Figures that follow may be used in many different drilling assemblies. The following exemplary systems provide only some of the representative assemblies within which the present invention may be used, but these should not be considered the only assemblies. In particular, the preferred embodiments of the expandable tool of the present invention may be used in any assembly requiring an expandable underreamer and/or stabilizer for use in controlling the directional tendencies of a drilling assembly in an expanded borehole.  
         [0044]      FIGS. 1-3  show various exemplary drilling assemblies within which the preferred embodiments of the present invention may be utilized. Referring initially to  FIG. 1 , a section of a drilling assembly generally designated as  100  is shown drilling into the bottom of a formation  10  with a conventional drill bit  110  followed by an underreamer  120 . Separated from the underreamer  120  by one or more drill collars  130  is a stabilizer  150  that controls the directional tendencies of the drilling assembly  100  in the underreamed borehole  25 . This section of the drilling assembly  100  is shown at the bottom of formation  10  drilling a borehole  20  with the conventional drill bit  110 , while the underreamer cutting arms  125  are simultaneously opening a larger diameter borehole  25  above. The drilling assembly  100  is operating below any cased portions of the well.  
         [0045]     As described previously, the underreamer  120  tends to provide a fulcrum or pivot effect to the drill bit  110 , thereby requiring a stabilizer  150  to offset this effect. In the preferred embodiment of the drilling assembly  100 , various embodiments of the expandable tool of the present invention are provided in the positions of both the underreamer  120  and the stabilizer  150 . In the most preferred embodiment, the stabilizer  150  would also preferably include cutting structures to ensure that the larger borehole  25  is enlarged to the proper diameter. However, any conventional underreamer may alternatively be utilized with one embodiment of the present invention provided in the position of stabilizer  150  in the drilling assembly  100 . Further, one embodiment of the present invention may be utilized in the position of underreamer  120 , and a conventional stabilizer may be utilized in the position of stabilizer  150 .  
         [0046]     Referring now to  FIG. 2 , where like numerals represent like components, a drilling assembly  200  is shown disposed within formation  10 , below any cased sections of the well. The drilling assembly  200  is drilling a borehole  20  utilizing a conventional drill bit  110  followed by a winged reamer  220 . The winged reamer  220  may be separated from the drill bit  110  by one or more drill collars  130 , but preferably the winged reamer  220  is connected directly above the drill bit  110 . Upstream of the winged reamer  220 , separated by one or more drill collars  130 , is a stabilizer  150  that controls the directional tendencies of the drilling assembly  200  in the underreamed borehole  25 . The drill bit  110  is shown at the bottom of the formation  10  drilling a borehole  20 , while the wing component  225  of the winged reamer  220  is simultaneously opening a larger diameter borehole  25  above. In the preferred assembly  200 , a preferred embodiment of the present invention would be located in the position of stabilizer  150 . In a most preferred assembly  200 , the stabilizer  150  would also include cutting structures to ensure that the larger borehole  25  is enlarged to the proper diameter.  
         [0047]     Referring to  FIG. 3 , where like numerals represent like components, again a drilling assembly  300  is shown disposed within formation  10 , below any cased sections of the well. The drilling assembly  300  utilizes a bi-center bit  320  that includes a pilot bit  310  and an eccentric underreamer bit  325 . As the pilot bit  310  drills the borehole  20 , the eccentric underreamer bit  325  opens a larger diameter borehole  25  above. The bi-center bit  320  is separated by one or more drill collars  130  from a stabilizer  150  designed to control the directional tendencies of the bi-center bit  320  in the underreamed borehole  25 . Again, the function of the stabilizer  150  is to offset the fulcrum or pivot effect created by the eccentric underreamer bit  325  to ensure that the pilot bit  310  stays centered as it drills the borehole  20 . In the preferred embodiment of the drilling assembly  300 , one embodiment of the expandable tool of the present invention would be located in the position of stabilizer  150 . In a most preferred assembly  300 , the stabilizer  150  would also include cutting structures to ensure that the larger borehole  25  is enlarged to the proper diameter.  
         [0048]     Referring now to  FIGS. 4 and 5 , one embodiment of the expandable tool of the present invention, generally designated as  500 , is shown in a collapsed position in  FIG. 4  and in an expanded position in  FIG. 5 . The expandable tool  500  comprises a generally cylindrical tool body  510  with a flowbore  508  extending therethrough. The tool body  510  includes upper  514  and lower  512  connection portions for connecting the tool  500  into a drilling assembly. In approximately the axial center of the tool body  510 , one or more pocket recesses  516  are formed in the body  510  and spaced apart azimuthally around the circumference of the body  510 . The one or more recesses  516  accommodate the axial movement of several components of the tool  500  that move up or down within the pocket recesses  516 , including one or more moveable, non-pivotable tool arms  520 . Each recess  516  stores one moveable arm  520  in the collapsed position. The preferred embodiment of the expandable tool includes three moveable arms  520  disposed within three pocket recesses  516 . In the discussion that follows, the one or more recesses  516  and the one or more arms  520  may be referred to in the plural form, i.e. recesses  516  and arms  520 . Nevertheless, it should be appreciated that the scope of the present invention also comprises one recess  516  and one arm  520 .  
         [0049]     The recesses  516  further include angled channels  518  that provide a drive mechanism for the moveable tool arms  520  to move axially upwardly and radially outwardly into the expanded position of  FIG. 5 . A biasing spring  540  is preferably including to bias the arms  520  to the collapsed position of  FIG. 4 . The biasing spring  540  is disposed within a spring cavity  545  and covered by a spring retainer  550 . Retainer  550  is locked in position by an upper cap  555 . A stop ring  544  is provided at the lower end of spring  540  to keep the spring  540  in position.  
         [0050]     Below the moveable arms  520 , a drive ring  570  is provided that includes one or more nozzles  575 . An actuating piston  530  that forms a piston cavity  535 , engages the drive ring  570 . A drive ring block  572  connects the piston  530  to the drive ring  570  via bolt  574 . The piston  530  is adapted to move axially in the pocket recesses  516 . A lower cap  580  provides a lower stop for the axial movement of the piston  530 . An inner mandrel  560  is the innermost component within the tool  500 , and it slidingly engages a lower retainer  590  at  592 . The lower retainer  590  includes ports  595  that allow drilling fluid to flow from the flowbore  508  into the piston chamber  535  to actuate the piston  530 .  
         [0051]     A threaded connection is provided at  556  between the upper cap  555  and the inner mandrel  560  and at  558  between the upper cap  555  and body  510 . The upper cap  555  sealingly engages the body  510  at  505 , and sealingly engages the inner mandrel  560  at  562  and  564 . A wrench slot  554  is provided between the upper cap  555  and the spring retainer  550 , which provides room for a wrench to be inserted to adjust the position of the spring retainer  550  in the body  510 . Spring retainer  550  connects at  551  via threads to the body  510 . Towards the lower end of the spring retainer  550 , a bore  552  is provided through which a bar can be placed to prevent rotation of the spring retainer  550  during assembly. For safety purposes, a spring cover  542  is bolted at  546  to the stop ring  544 . The spring cover  542  prevents personnel from incurring injury during assembly and testing of the tool  500 .  
         [0052]     The moveable arms  520  include pads  522 ,  524 , and  526  with structures  700 ,  800  that engage the borehole when the arms  520  are expanded outwardly to the expanded position of the tool  500  shown in  FIG. 5 . Below the arms  520 , the piston  530  sealingly engages the inner mandrel  560  at  566 , and sealingly engages the body  510  at  534 . The lower cap  580  is threadingly connected to the body and to the lower retainer  590  at  582 ,  584 , respectively. A sealing engagement is also provided at  586  between the lower cap  580  and the body  510 . The lower cap  580  provides a stop for the piston  530  to control the collapsed diameter of the tool  500 .  
         [0053]     Several components are provided for assembly rather than for functional purposes. For example, the drive ring  570  is coupled to the piston  530 , and then the drive ring block  572  is boltingly connected at  574  to prevent the drive ring  570  and the piston  530  from translating axially relative to one another. The drive ring block  572 , therefore, provides a locking connection between the drive ring  570  and the piston  530 .  
         [0054]      FIG. 5  depicts the tool  500  with the moveable arms  520  in the maximum expanded position, extending radially outwardly from the body  510 . Once the tool  500  is in the borehole, it is only expandable to one position. Therefore, the tool  500  has two operational positions—namely a collapsed position as shown in  FIG. 4  or an expanded position as shown in  FIG. 5 . However, the spring retainer  550 , which is a threaded sleeve, can be adjusted at the surface to limit the full diameter expansion of arms  520 . The spring retainer  550  compresses the biasing spring  540  when the tool  500  is collapsed, and the position of the spring retainer  550  determines the amount of expansion of the arms  520 . The spring retainer  550  is adjusted by a wrench in the wrench slot  554  that rotates the spring retainer  550  axially downwardly or upwardly with respect to the body  510  at threads  551 . The upper cap  555  is also a threaded component that locks the spring retainer  550  once it has been positioned. Accordingly, one advantage of the present tool is the ability to adjust at the surface the expanded diameter of the tool  500 . Unlike conventional underreamer tools, this adjustment can be made without replacing any components of the tool  500 .  
         [0055]     In the expanded position shown in  FIG. 5 , the arms  520  will either underream the borehole or stabilize the drilling assembly, depending upon how the pads  522 ,  524  and  526  are configured. In the configuration of  FIGS. 5 , cutting structures  700  on pads  526  would underream the borehole. Wear buttons  800  on pads  522  and  524  would provide gauge protection as the underreaming progresses. Hydraulic force causes the arms  520  to expand outwardly to the position shown in  FIG. 5  due to the differential pressure of the drilling fluid between the flowbore  508  and the annulus  22 .  
         [0056]     The drilling fluid flows along path  605 , through ports  595  in the lower retainer  590 , along path  610  into the piston chamber  535 . The differential pressure between the fluid in the flowbore  508  and the fluid in the borehole annulus  22  surrounding tool  500  causes the piston  530  to move axially upwardly from the position shown in  FIG. 4  to the position shown in  FIG. 5 . A small amount of flow can move through the piston chamber  535  and through nozzles  575  to the annulus  22  as the tool  500  starts to expand. As the piston  530  moves axially upwardly in pocket recesses  516 , the piston  530  engages the drive ring  570 , thereby causing the drive ring  570  to move axially upwardly against the moveable arms  520 . The arms  520  will move axially upwardly in pocket recesses  516  and also radially outwardly as the arms  520  travel in channels  518  disposed in the body  510 . In the expanded position, the flow continues along paths  605 ,  610  and out into the annulus  22  through nozzles  575 . Because the nozzles  575  are part of the drive ring  570 , they move axially with the arms  520 . Accordingly, these nozzles  575  are optimally positioned to continuously provide cleaning and cooling to the cutting structures  700  disposed on surface  526  as fluid exits to the annulus  22  along flow path  620 .  
         [0057]     The underreamer tool  500  of the one embodiment of the present invention solves the problems experienced with bi-center bits and winged reamers because it is designed to remain concentrically disposed within the borehole. In particular, the tool  500  of the present invention preferably includes three extendable arms  520  spaced apart circumferentially at the same axial location on the tool  510 . In the preferred embodiment, the circumferential spacing would be 120° apart. This three arm design provides a full gauge underreaming tool  500  that remains centralized in the borehole at all times.  
         [0058]     Another feature of the preferred embodiments of the present invention is the ability of the tool  500  to provide hydraulic indication at the surface, thereby informing the operator whether the tool is in the contracted position shown in  FIG. 4 , or the expanded position shown in  FIG. 5 . Namely, in the contracted position, the flow area within piston chamber  535  is smaller than the flow area within piston chamber  535  when the tool  500  is in the expanded position shown in  FIG. 5 . Therefore, in the expanded position, the flow area in chamber  535  is larger, providing a greater flow area between the flowbore  508  and the wellbore annulus  22 . In response, pressure at the surface will decrease as compared to the pressure at the surface when the tool  500  is contracted. This decrease in pressure indicates that the tool  500  is expanded.  
         [0059]      FIGS. 6-10  provide more detail regarding the moveable arms  520  and drive ring  570  of  FIGS. 4 and 5 .  FIG. 6  shows a “blank” arm  520  with no cutting structures or stabilizing structures attached to pads  522 ,  524 ,  526 . The arm  520  is shown in isometric view to depict a top surface  521 , a bottom surface  527 , a front surface  665 , a back surface  660 , and a side surface  528 . The top surface  521  and the bottom surface  527  are preferably angled, as described in more detail below. The arm  520  preferably includes two upper pads  522 , one middle pad  524 , and two lower pads  526  disposed on the front surface  665  of the arm  520 . The arm  520  also includes extensions  650  disposed along each side  528  of arm  520 . The extensions  650  preferably extend upwardly at an angle from the bottom  527  of the arm  520  towards pads  522 ,  524  and  526 . The extensions  650  protrude outwardly from the arm  520  to fit within corresponding channels  518  in the pocket recess  516  of the tool body  510 , as shown in  FIGS. 4 and 5 . The interconnection between the arm extensions  650  and the body channels  518  increases the surface area of contact between the moveable arms  520  and the tool body  510 , thereby providing a more robust expandable tool  500  as compared to prior art tools. The arm  520  depicted in  FIG. 6  is a blank version of either an underreamer cutting arm or a stabilizer arm. By changing the structures disposed on pads  522 ,  524  and  526 , the tool  500  is converted from an underreamer to a stabilizer or vice versa, or to a combination underreamer/stabilizer.  
         [0060]     Referring now to  FIGS. 7, 8  and  9 , an exemplary arm  520  is shown that includes two sets of cutting structures  700 ,  710 .  FIG. 7  depicts the arm  520  from a top perspective,  FIG. 8  provides an elevational side view, and  FIG. 9  shows an isometric perspective. The top surface  521  and the bottom surface  527  of the arm  520  are preferably angled in the same direction as best shown in  FIG. 7 . These surfaces  521 ,  527  are designed to prevent the arm  520  from vibrating when pads  522 ,  524  and  526  engage the borehole. Namely, when pads  522 ,  524  and  526  engage the borehole, the arms  520  are held in compression by the piston  530 . The angled top surface  521  and the angled bottom surface  527  bias the arms  520  to the trailing side of the pocket recesses  516  to minimize vibration.  
         [0061]     In the top view of  FIG. 7 , pads  522  comprise cutting structures  710  such that the arm  520  provides back reaming capabilities. Back reaming is pulling the tool  500  upwardly in the borehole while underreaming. Pad  524  is preferably covered with wear buttons  800  that provide a stabilizing and gauge protection function. Pads  526  comprise cutting structures  700  for underreaming. In the side view of  FIG. 8 , the extensions  650  that fit within channels  518  of the body  510  are shown extending upwardly at an angle along the side  528  from the back surface  660  of the arm  520  towards pads  522 ,  524  and  526 .  FIG. 9  shows the same arm  520  in isometric view.  
         [0062]     To change the arm  520  shown in  FIGS. 7, 8 , and  9  from a back reaming and underreaming arm to simply an underreaming arm, the back reaming cutting structures  710  would be replaced with wear buttons, such as buttons  800 . This configuration would result in the underreaming arm  520  shown in  FIGS. 4 and 5 . Modifying the tool  500  from an underreamer to a stabilizer simply requires providing stabilizing structures on all of the pads  522 ,  524  and  526 . As a stabilizer, surfaces  522 ,  524 , and  526  would be covered with a dense plurality of wear buttons  800  without any cutting structures. The preferred material for the wear buttons  800  is a tungsten carbide or diamond material, which provides good wear capabilities. In an alternative embodiment, the pads  522 ,  524 , and  526  may be coated with a hardened material called TCI 300H hardfacing.  
         [0063]     Accordingly, the pads  522 ,  524 ,  526  could comprise a variety of structures and configurations utilizing a variety of different materials. When the tool is used in an underreaming function, a variety of different cutting structures  700  could be provided on surfaces  526 , depending upon the formation characteristics. Preferably, the cutting structures  700 ,  710  for underreaming and back reaming, respectively, are specially designed for the particular cutting function. More preferably, the cutting structures  700 ,  710  comprise the cutting structures disclosed and claimed in co-pending U.S. patent application Ser. No. 09/924,961, filed Aug. 8, 2001, entitled “Advanced Expandable Reaming Tool,” assigned to Smith International, Inc., which is hereby incorporated herein by reference.  
         [0064]     Referring now to  FIG. 10 , additional advantages of the preferred embodiments of the present invention are provided by the one or more nozzles  575  disposed in the drive ring  570 . The underreamer/stabilizer of the preferred embodiments of the present invention preferably includes three moveable arms  520  spaced apart circumferentially at the same axial location along the tool body  510 . In the preferred embodiment, the three moveable arms  520  are spaced 120° circumferentially. This arrangement of the arms  520  is preferred to centralize the tool  500  in the borehole. The drive ring  570  is moveable with the arms  520  and preferably includes three extended portions  576  spaced 120° circumferentially with angled nozzles  575  therethrough that are designed to direct drilling fluid to the cutting structures  700  of the underreamer at surfaces  526 . The boreholes  578  in the extended portions  576  adjacent nozzles  575  accept bolts  574  to connect the drive ring  570  to the drive ring block  572  and piston  530 . An aperture  571  is disposed through the center of the drive ring  570  to enable a connection to the piston  530 . Because the drive ring  570  is connected to the piston  530 , it moves with the piston  530  to push the moveable arms  520  axially upwardly and outwardly along the channels  518  to the expanded position. Accordingly, because drive ring  570  moves with the arms  520 , the nozzles  575  continuously provide drilling fluid to the cutting structures  700  on the underreamer surfaces  526 . The nozzles  575  are optimally placed to move with and follow the cutting structures  700  and thereby assure that the cutters  700  are properly cleaned and cooled at all times.  
         [0065]      FIGS. 11 and 12  depict a second embodiment of the present invention, generally designated as  900 , in the collapsed and expanded positions, respectively. Many components of tool  900  are the same as the components of embodiment  500 , and those components maintain the same reference numerals. There are, however, several differences. The inner mandrel  560  of the first embodiment tool  500  is replaced by a stinger assembly  910 , preferably comprising an upper inner mandrel  912 , a middle inner mandrel  914 , and a lower inner mandrel  916 . The lower inner mandrel  916  includes ports  920  that must align with ports  595  in the lower retainer  590  before fluid can enter piston chamber  535  to actuate the piston  530 . As shown in  FIG. 11 , fluid flows through the flowbore  508  of tool  900 , along pathway  605  depicted by the arrows. Because the ports  920  of the lower inner mandrel  916  do not align with the ports  595  of the lower retainer  590 , the fluid continues flowing along path  605 , past ports  595 , down through the tool  900 .  
         [0066]     The tool  900  is selectively actuated utilizing an actuator (not shown), which aligns the ports  920  with the ports  595  to enable the expandable tool to move from the contracted position shown in  FIG. 11  to the expanded position shown in  FIG. 12 . Below lower inner mandrel  916 , a bottom spring  930  is disposed within a bottom spring chamber  935  and held within the body  510  by a bottom spring retainer  950 . Bottom spring retainer  950  threadingly connects at  952  to the lower retainer  590 . The spring  930  biases the stinger assembly  910  upwardly such that stinger  910  must be forced downwardly by an actuator to overcome the force of bottom spring  930 . By moving the stinger  910  downwardly, the ports  920  disposed circumferentially around the bottom of lower inner mandrel  916  align with the ports  595  of lower retainer  590  that lead into piston chamber  535 .  
         [0067]      FIG. 12  shows the tool  900  in an expanded position. In this position, drilling fluid flows through the flowbore  508 , along pathway  605 . However, because stinger  910  has been actuated downwardly against the force of bottom spring  930  by an actuator, the ports  920  in lower inner mandrel  916  now align with ports  595  in the lower retainer  590 . Therefore, when the drilling fluid proceeds downwardly along flow path  605  through the flowbore  508  to reach ports  920 , it will flow through ports  920 ,  595  and into the piston chamber  535  as depicted by flow arrows  610 .  
         [0068]     Due to the differential pressure between the flowbore  508  and the wellbore annulus  22  surrounding tool  900 , the fluid flowing along pathway  610  will actuate the piston  530  upwardly against the force of spring  540 . The piston  530  will push the drive ring  570 , which will push the arms  520  axially upwardly and outwardly as the extensions  650  on the arms  520  move along channels  518  in the body  510 . Once the fluid flows through the nozzles  575  in the drive ring  570 , it exits at an angle along pathway  620  to cool and clean the cutting structures  700  disposed on surfaces  526  that underream the borehole. Accordingly, the second embodiment  900  of  FIGS. 11 and 12  is capable of being selectively actuated. Namely, by engaging the upper surface  975  of stinger  910  with an actuator, the tool  900  can be selectively actuated at the election of the operator to align the ports  920  and  595 . The preferred actuator is the flow switch described and claimed in U.S. Pat. No. 6,289,999 entitled “Fluid Flow Control Devices and Methods for Selective Actuation of Valves and Hydraulic Drilling Tools,” hereby incorporated herein by reference.  
         [0069]     Referring again to  FIGS. 11 and 12 , typically a gap is provided between the upper end  975  of the stinger  910  and the actuator when the tool is in the collapsed position. That gap length must be maintained to ensure that actuation occurs only when it is meant to occur. Accordingly, upper inner mandrel  912  may include an adjustment ring portion  918 , which is just a spacer ring that makes up any discrepancies in the area between the upper inner mandrel  912  and the middle inner mandrel  914  such that the appropriate gap dimension can be maintained.  
         [0070]     As one of ordinary skill in the art will readily appreciate, any actuating mechanism can be utilized to selectively actuate the tool  900  of  FIGS. 11 and 12 . However, the preferred flow switch provides the advantage of additional hydraulic indications to the surface, in addition to the pressure indications provided by the increased flow area in the piston chamber  535  when the tool  900  is in the expanded position of  FIG. 12 . Namely, the preferred flow switch includes an uplink pulser capable of providing position and status information to the surface via mud pulse telemetry. Accordingly, the preferred embodiment comprises the tool  900  of  FIGS. 11 and 12 , and more preferably comprises the tool  900  in combination with the referenced flow switch.  
         [0071]     In operation, an expandable tool  500  or  900  is lowered through casing in the collapsed position shown in  FIGS. 4 and 11 , respectively. The first embodiment of the tool  500  would then be expanded automatically when drilling fluid flows through flowbore  508 , and the second embodiment of the tool  900  would be expanded only after selectively actuating the tool  900 . Whether the selective actuation feature is present or not, the tools  500 ,  900  expand due to differential pressure between the flow bore  508  and the wellbore annulus  22  acting on the piston  530 . That differential pressure may be in the range of 800 to 1,500 psi. Therefore, differential pressure working across the piston  530  will cause the one or more arms  520  of the tool to move from a collapsed to an expanded position against the force of the biasing spring  540 .  
         [0072]     Before the drilling assembly is lowered into the borehole, the function of the present invention as either an underreamer or as a stabilizer would be determined. Referring again to  FIG. 1 , one example would be to use either embodiment of the tool  500 ,  900  in the position of underreamer  120 , and preferably to use the second embodiment of the tool  900  in the position of stabilizer  150 . As another example, referring to  FIGS. 2 and 3 , if a winged reamer  220  or a bi-center bit  320  is used instead of an underreamer  120 , the second embodiment of the tool  900  would preferably be used in the position of stabilizer  150 . As an underreamer, the preferred embodiments of the present invention are capable of underreaming a borehole to a desired diameter. As a stabilizer, the preferred embodiments of the present invention provide directional control for the assembly  100 ,  200 ,  300  within the underreamed borehole  25 .  
         [0073]     In summary, the various embodiments of the expandable tool of the present invention may be used as an underreamer to enlarge a borehole below a restriction to a larger diameter. Alternatively, the various embodiments of the expandable tool may be used to stabilize a drilling system in a previously underreamed borehole, or in a borehole that is being underreamed while drilling progresses. The various embodiments of the present invention solve the problems of the prior art and include other features and advantages. Namely, the embodiments of the present expandable tool are stronger and have a higher hydraulic capacity than prior art underreamers. The preferred embodiments of the tool also provide pressure indications at the surface regarding whether the tool is collapsed or expanded. The tool preferably includes a novel assembly for moving the arms to the expanded position. Yet another advantage of the preferred embodiments is that the tool can be used in conjunction with other conventional devices such as a winged reamer or a bi-center bit to ensure that they function properly. The preferred embodiments of the tool further include one or more optimally placed and moveable nozzles for cleaning and cooling the cutting structures. Finally, the preferred embodiments of the present invention allow for adjustable expanded diameters without component changes.  
         [0074]     While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims which follow, the scope of which shall include all equivalents of the subject matter of the claims.