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CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/247,112, filed Sep. 30, 2009, the disclosure of which is hereby incorporated herein in its entirety by this reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to an expandable apparatus for use in drilling or enlarging a subterranean borehole and, more particularly, to an expandable apparatus for enlarging a subterranean borehole beneath a casing or liner. 
     BACKGROUND 
     Expandable reamers are typically employed for enlarging subterranean boreholes. Conventionally, in drilling oil, gas, and geothermal wells, casing is installed and cemented to prevent the well bore walls from caving into the subterranean borehole while providing requisite shoring for subsequent drilling operation to achieve greater depths. Casing is also conventionally installed to isolate different formations, to prevent cross flow of formation fluids, and to enable control of formation fluids and pressure as the borehole is drilled. To increase the depth of a previously drilled borehole, new casing is laid within and extended below the previous casing. While adding additional casing allows a borehole to reach greater depths, it has the disadvantage of narrowing the borehole. Narrowing the borehole restricts the diameter of any subsequent sections of the well because the drill bit and any further casing must pass through the existing casing. As reductions in the borehole diameter are undesirable because they limit the production flow rate of oil and gas through the borehole, it is often desirable to enlarge a subterranean borehole to provide a larger borehole diameter for installing additional casing beyond previously installed casing as well as to enable better production flow rates of hydrocarbons through the borehole. 
     A variety of approaches have been employed for enlarging a borehole diameter. One conventional approach used to enlarge a subterranean borehole includes using eccentric and bi-center bits. For example, an eccentric bit with a laterally extended or enlarged cutting portion is rotated about its axis to produce an enlarged borehole diameter. An example of an eccentric bit is disclosed in U.S. Pat. No. 4,635,738, which is assigned to the assignee of the present invention. A bi-center bit assembly employs two longitudinally superimposed bit sections with laterally offset axes, which, when rotated, produce an enlarged borehole diameter. An example of a bi-center bit is disclosed in U.S. Pat. No. 5,957,223, which is also assigned to the assignee of the present invention. 
     Another conventional approach used to enlarge a subterranean borehole includes employing an extended bottom-hole assembly with a pilot drill bit at the distal end thereof and a reamer assembly some distance above the pilot drill bit. This arrangement permits the use of any standard rotary drill bit type (e.g., a rock bit or a drag bit), as the pilot bit and the extended nature of the assembly permit greater flexibility when passing through tight spots in the borehole as well as the opportunity to effectively stabilize the pilot drill bit so that the pilot drill bit and the following reamer will traverse the path intended for the borehole. This aspect of an extended bottom hole assembly is particularly significant in directional drilling. The assignee of the present invention has, to this end, designed as reaming structures so called “reamer wings,” which generally comprise a tubular body having a fishing neck with a threaded connection at the top thereof and a tong die surface at the bottom thereof, also with a threaded connection. U.S. Pat. No. RE36,817 and U.S. Pat. No. 5,495,899, both of which are assigned to the assignee of the present invention, disclose reaming structures including reamer wings. The upper midportion of the reamer wing tool includes one or more longitudinally extending blades projecting generally radially outwardly from the tubular body and PDC cutting elements are provided on the blades. 
     As mentioned above, conventional expandable reamers may be used to enlarge a subterranean borehole and may include blades that are pivotably or hingedly affixed to a tubular body and actuated by way of a piston disposed therein as disclosed by, for example, U.S. Pat. No. 5,402,856 to Warren. In addition, U.S. Pat. No. 6,360,831 to Åkesson et al., discloses a conventional borehole opener comprising a body equipped with at least two hole opening arms having cutting means that may be moved from a position of rest in the body to an active position by exposure to pressure of the drilling fluid flowing through the body. The blades in these reamers are initially retracted to permit the tool to be run through the borehole on a drill string, and, once the tool has passed beyond the end of the casing, the blades are extended so the bore diameter may be increased below the casing. In addition, United States Patent Application Publication No. U.S. 2008/0128175 A1, which application was filed Dec. 3, 2007 and entitled “Expandable Reamers for Earth-Boring Applications,” discloses additional expandable reamer apparatus, the entire disclosure of which is incorporated herein by this reference. 
     BRIEF SUMMARY 
     In some embodiments, the present invention includes expandable apparatus for use in a subterranean borehole. The expandable apparatus include a tubular body having at least one opening in a wall of the tubular body and a drilling fluid flow path extending therethrough. At least one member may be positioned within the at least one opening in the wall of the tubular body wherein the at least one member is configured to move between a retracted position and an extended position. The expandable apparatus also includes a push sleeve at least partially disposed in the tubular body and coupled to the at least one member. The push sleeve is configured to move axially upward responsive to a pressure of drilling fluid passing through the drilling fluid flow path to extend the at least one member into the extended position. The push sleeve is also configured to move axially downward in response to a pressure of drilling fluid upon a restrictive element disposed within the fluid passageway to retract the at least one member into the retracted position. 
     In additional embodiments, the present invention includes methods of forming an expandable apparatus for use in drilling or enlarging a borehole in a subterranean formation. The method includes forming a tubular body having at least one opening in a wall of the tubular body and having a drilling fluid flow path extending therethrough. At least one member is positioned within the opening in the wall of the tubular body and configured to move between an extended position and a retracted position. A push sleeve is disposed at least partially within the tubular body coupled to the at least one member. The push sleeve is configured to move axially upward responsive to a pressure of drilling fluid passing through the drilling fluid flow path to extend the at least one member into the extended position and to move axially downward in response to a pressure of drilling fluid upon a restrictive element disposed within the fluid passageway to retract the at least one member into the retracted position. 
     In yet additional embodiments, the present invention includes methods of moving at least one extendable member of an earth-boring tool. The method includes flowing a drilling fluid through a drilling fluid passageway extending through a push sleeve disposed within a tubular body of the earth-boring tool. The push sleeve moves axially upward in response to a pressure of the fluid upon the push sleeve and extends the at least one extendable member coupled to the push sleeve. The method further includes disposing a restrictive element within the drilling fluid passageway and the push sleeve moves axially downward in response to a pressure of the fluid upon the restrictive element and retracts the at least one extendable member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming what are regarded as embodiments of the invention, various features and advantages of embodiments of the invention may be more readily ascertained from the following description of some embodiments of the invention, when read in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a side view of an embodiment of an expandable reamer apparatus of the invention; 
         FIG. 2  shows a transverse cross-sectional view of the expandable reamer apparatus as indicated by section line  2 - 2  in  FIG. 1 ; 
         FIG. 3  shows a longitudinal cross-sectional view of one embodiment of the expandable reamer apparatus shown in  FIG. 1  in the initial tool position prior to actuation of the blades; 
         FIG. 4  shows a longitudinal cross-sectional view of the expandable reamer apparatus shown in  FIG. 3  in which the blades (one depicted) are held in the fully extended position by the push sleeve under the influence of fluid pressure; 
         FIG. 5  shows an enlarged cross-sectional view of the expandable reamer apparatus shown in  FIG. 3  in which the blades (one depicted) are held in the fully retracted position by the push sleeve under the influence of fluid pressure caused by the addition of a restrictive element to the expandable reamer apparatus. 
         FIG. 6  shows an enlarged cross-sectional view of the expandable reamer apparatus shown in  FIG. 3  in which the blades (one depicted) are held in the fully expanded position by the push sleeve under the influence of fluid pressure after the restrictive element has been expelled from the expandable reamer apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The illustrations presented herein are, in some instances, not actual views of any particular reamer tool, cutting element, or other feature of a reamer tool, but are merely idealized representations that are employed to describe embodiments of the present invention. Additionally, elements common between figures may retain the same numerical designation. 
     Various embodiments of the disclosure are directed to an expandable apparatus. By way of example and not limitation, an expandable apparatus may comprise an expandable reamer apparatus, an expandable stabilizer apparatus or similar apparatus.  FIG. 1  illustrates an expandable apparatus  100  according to an embodiment of the disclosure comprising an expandable reamer. The expandable apparatus  100  may be similar to the expandable apparatus described in U.S. Patent Publication No. 2008/0128175, the entire disclosure of which is incorporated herein by this reference. 
     The expandable apparatus  100  in the form of an expandable reamer may include a generally cylindrical tubular body  108  having a longitudinal axis L 8 . The tubular body  108  of the expandable apparatus  100  may have a lower end  190  and an upper end  191 . The terms “lower” and “upper,” as used herein with reference to the ends  190 ,  191 , refer to the typical positions of the ends  190 ,  191  relative to one another when the expandable apparatus  100  is positioned within a well bore. The lower end  190  of the tubular body  108  of the expandable apparatus  100  may include a set of threads (e.g., a threaded male pin member) for connecting the lower end  190  to another section of a drill string or another component of a bottom-hole assembly (BHA), such as, for example, a drill collar or collars carrying a pilot drill bit for drilling a well bore. Similarly, the upper end  191  of the tubular body  108  of the expandable apparatus  100  may include a set of threads (e.g., a threaded female box member) for connecting the upper end  191  to another section of a drill string or another component of a bottom-hole assembly (BHA). 
     Three sliding members such as, for example, cutter blocks or blades  101 ,  102 ,  103  (see  FIG. 2 ) are positionally retained in circumferentially spaced relationship in the tubular body  108 , as further described below, and may be provided at a position along the expandable apparatus  100  intermediate the first lower end  190  and the second upper end  191 . The blades  101 ,  102 ,  103  may be comprised of steel, tungsten carbide, a particle-matrix composite material (e.g., hard particles dispersed throughout a metal matrix material), or other suitable materials as known in the art. The blades  101 ,  102 ,  103  are retained in an initial, retracted position within the tubular body  108  of the expandable apparatus  100  as illustrated in  FIG. 3 , but may be moved responsive to application of hydraulic pressure into the extended position (shown in  FIGS. 4 and 6 ) and moved into a retracted position (shown in  FIG. 5 ) when desired, as will be described herein. The expandable apparatus  100  may be configured such that the blades  101 ,  102 ,  103  engage the walls of a subterranean formation surrounding a well bore in which apparatus  100  is disposed to remove formation material when the blades  101 ,  102 ,  103  are in the extended position, but are not operable to so engage the walls of a subterranean formation within a well bore when the blades  101 ,  102 ,  103  are in the retracted position. While the expandable apparatus  100  includes three blades  101 ,  102 ,  103 , it is contemplated that one, two or more than three blades may be utilized to advantage. Moreover, while the blades  101 ,  102 ,  103  are symmetrically circumferentially positioned about the longitudinal axis L 8  along the tubular body  108 , the blades may also be positioned circumferentially asymmetrically as well as asymmetrically about the longitudinal axis L 8 . 
     The expandable apparatus  100  may, optionally, include a plurality of stabilizer blocks  105 ,  106 ,  107 . In some embodiments, the mid stabilizer block  106  and the lower stabilizer block  107  may be combined into a unitary stabilizer block. The stabilizer blocks  105 ,  106 ,  107  help to center the expandable apparatus  100  in the drill hole while being run into position through a casing or liner string and also while drilling and reaming the borehole. In other embodiments, no stabilizer blocks may be employed. In such embodiments, the tubular body may comprise a larger outer diameter in the longitudinal portion where the stabilizing blocks are shown in  FIG. 1  to provide a similar centering function as provided by the stabilizing blocks. 
     The upper stabilizer block  105  may be used to stop or limit the forward motion of the blades  101 ,  102 ,  103  (see also  FIG. 3 ), determining the extent to which the blades  101 ,  102 ,  103  may engage a bore hole while drilling. The upper stabilizer block  105 , in addition to providing a back stop for limiting the lateral extent of the blades, may provide for additional stability when the blades  101 ,  102 ,  103  are retracted and the expandable apparatus  100  of a drill string is positioned within a bore hole in an area where an expanded hole is not desired while the drill string is rotating. Advantageously, the upper stabilizer block  105  may be mounted, removed and/or replaced by a technician, particularly in the field, allowing the extent to which the blades  101 ,  102 ,  103  engage the bore hole to be readily increased or decreased to a different extent than illustrated. Optionally, it is recognized that a stop associated on a track side of the upper stabilizer block  105  may be customized in order to arrest the extent to which the blades  101 ,  102 ,  103  may laterally extend when fully positioned to the extended position along blade tracks  148 . The stabilizer blocks  105 ,  106 ,  107  may include hard faced bearing pads (not shown) to provide a surface for contacting a wall of a bore hole while stabilizing the apparatus therein during a drilling operation. 
       FIG. 2  is a cross-sectional view of the expandable apparatus  100  shown in  FIG. 1  taken along section line  2 - 2  shown therein. As shown in  FIG. 2 , the tubular body  108  encloses a fluid passageway  192  that extends longitudinally through the tubular body  108 . The fluid passageway  192  directs fluid substantially through an inner bore  151  of a push sleeve  210 . 
     Referring to  FIG. 2 , to better describe aspects of the invention, blades  102  and  103  are shown in the initial or retracted positions, while blade  101  is shown in the outward or extended position. The expandable apparatus  100  may be configured such that the outermost radial or lateral extent of each of the blades  101 ,  102 ,  103  is recessed within the tubular body  108  when in the initial or retracted positions so it may not extend beyond the greatest extent of outer diameter of the tubular body  108 . Such an arrangement may protect the blades  101 ,  102 ,  103  as the expandable apparatus  100  is disposed within a casing of a borehole, and may allow the expandable apparatus  100  to pass through such casing within a borehole. In other embodiments, the outermost radial extent of the blades  101 ,  102 ,  103  may coincide with or slightly extend beyond the outer diameter of the tubular body  108 . As illustrated by blade  101 , the blades may extend beyond the outer diameter of the tubular body  108  when in the extended position, to engage the walls of a borehole in a reaming operation. 
       FIG. 3  is another cross-sectional view of the expandable apparatus  100  shown in  FIGS. 1 and 2  taken along section line  3 - 3  shown in  FIG. 2 . Referring to  FIGS. 2 and 3 , the tubular body  108  positionally retrains three sliding cutter blocks or blades  101 ,  102 ,  103  in three respective blade tracks  148 . The blades  101 ,  102 ,  103 , each carry a plurality of cutting elements  205  for engaging the material of a subterranean formation defining the wall of an open borehole when the blades  101 ,  102 ,  103  are in an extended position (shown in  FIG. 4 ). The cutting elements  205  may be polycrystalline diamond compact (PDC) cutters or other cutting elements known to a person of ordinary skill in the art and as generally described in U.S. Pat. No. 7,036,611, which is incorporated herein in its entirety by this reference. 
     Referring to  FIG. 3 , the blades  101 ,  102 ,  103  are hingedly coupled to a push sleeve  210 . The push sleeve  210  is disposed within the tubular body  108  and configured to slide axially within the tubular body  108  in response to pressures applied at least one end surface of the push sleeve  210 . In some embodiments, the push sleeve  210  may be disposed in the tubular body  108  and may be configured similar to the push sleeve described by U.S. Patent Publication No. 2008/0128175 referenced above and biased by a spring as described therein. 
     The push sleeve  210  may comprise an upper portion  215  and a lower portion  220  at opposing longitudinal ends. The push sleeve  210  may be configured and positioned so that the upper portion  215  of the push sleeve  210  comprises a smaller annular surface area than the lower portion  220  of the push sleeve  210  to create a greater force on the lower portion  220  of the push sleeve  210  than on the upper portion  215  of the push sleeve  210  when a pressure is exerted on both portions by a pressurized fluid as described in more detail below. The lower portion  220  of the push sleeve  210  may be coupled to a ball trap sleeve  225  and the ball trap sleeve  225  may be coupled to a screen catch  230 . The ball trap sleeve  225  may comprise at least one protrusion  245  extending annularly from the push sleeve  210  to an inside wall of the tubular body  108 . The at least one protrusion  245  of the push sleeve  210  may include an upper surface  246  and a lower surface  247 . The screen catch  230  is configured to hold at least one expelled ball  300  ( FIG. 6 ) as described in further detail below, without impeding the fluid flow through the screen catch  230  and may comprise any kind of screened enclosure, as known in the art. The screen catch  230  may also include a removable cap (not shown) for removal of the at least one expelled ball  300  ( FIG. 6 ) when the expandable apparatus  100  is not in use. 
     The push sleeve  210  may include at least one fluid port  235  that may selectively communicate with a plurality of nozzle ports  240  extending through the tubular body  108  for directing a drilling fluid toward the blades  101 ,  102 ,  103  when the blades  101 ,  102 ,  103  are extended. The ball trap sleeve  225  may comprise at least one fluid port  250  in fluid communication with an annular chamber  255  located between an inner sidewall of the tubular body  108  and an outer surface of the ball trap sleeve  225  and also in communication with the lower surface  247  of the protrusion  245  of the ball trap sleeve  225 . The ball trap sleeve  225  also may include a ball seat  226  for receiving a ball  300  ( FIG. 5 ). The ball seat  226  may comprise, for example, a protrusion extending into the fluid passageway  192  configured to retain the ball  300 . A compression spring  260  that resists the motion of the push sleeve  210  toward the upper end  191  of the expandable apparatus  100  may be retained on an outer surface  275  of the push sleeve  210  between a ring  265  attached in a groove  266  of the tubular body  108  and the upper surface  246  of the protrusion  245  of the ball trap sleeve  225 . 
     In operation, the push sleeve  210  may be originally positioned toward the lower end  190  of the expandable apparatus  100 , as shown in  FIG. 3 , so that the expandable apparatus  100  may be lowered into a well bore without the blades  101 ,  102 ,  103  engaging the walls of a subterranean formation surrounding the well bore. The compression spring  260  may resist the motion of the push sleeve  210  toward the upper end  191  of the expandable reamer apparatus, thus maintaining the blades  101 ,  102 ,  103  in the retracted position. 
     As shown in  FIG. 4 , once the expandable apparatus  100  is positioned in the well bore, a fluid, such as a drilling fluid, may be flowed through the fluid passageway  192  in the direction of arrow  270 . Some of the fluid flowing through the fluid passageway  192  may travel through the fluid port  250  in the ball trap sleeve  225  into the annular chamber  255 , causing the fluid to pressurize the annular chamber  255 , exerting a force on the lower portion  220  of the push sleeve  210 . Concurrently, some of the fluid flowing through the fluid passageway  192  exerts a force on the upper portion  215  of the push sleeve  210 . As described above, the lower portion  220  of the push sleeve  210  has a larger surface area than the upper portion  215  of the push sleeve  210 . Therefore, with equal or substantially equal pressures applied to the upper portion  215  of the push sleeve  210  and the lower portion  220  of the push sleeve  210  by the fluid, the force applied on the lower portion  220  of the push sleeve  210  will be greater than the force applied on the upper portion  215  of the push sleeve  210  by virtue of the fact that force is equal to the area of the surface multiplied by the pressure applied to that area. The resultant net force is toward the upper end  191  of the expandable apparatus  100 . When the resultant net force is great enough to contract compression spring  260 , the push sleeve  210  slides upward, extending the blades  101 ,  102 ,  103 . In some embodiments, the pressurized fluid may also exert a force on the lower surface  247  of the protrusion  245  of the ball trap sleeve  225 , which provides an additional force toward the upper end  191  of the expandable apparatus  100  thus extending the blades  101 ,  102 ,  103 . 
     As shown in  FIG. 5 , when it is desired to retract the blades  101 ,  102 ,  103 , drilling fluid flow may be momentarily ceased, if required, and a ball  300  may be dropped into the drill string and pumping of drilling fluid resumed. While the ball  300  is described herein, it is understood that any restrictive element may be used instead of the ball  300  or more than one ball  300  may be used. In some embodiments, the ball  300  may comprise a malleable and/or compressible material such as, for example, nylon, brass, lead rubber, hydrogenated nitrile butadiene rubber (HNBR), nitrile butadiene rubber (NBR), and other polymers and malleable materials known in the art. The ball  300  moves down the expandable apparatus  100  via gravity and/or fluid flow toward the lower end  190  of the expandable apparatus  100  where the ball  300  may become lodged in the ball seat  226  of the ball trap sleeve  225 . When the ball  300  is lodged in the ball seat  226 , the drilling fluid exerts a force on a surface  305  of the ball  300  in the direction of the lower end  190  of the expandable apparatus  100 . The combined surface area of the surface  305  of the ball  300  and the upper portion  215  of the push sleeve  210  is greater than the surface area of the lower portion  220  of the push sleeve  210  Therefore, with equal or substantially equal pressures applied to the surface  305  of the ball  300 , the upper portion  215  of the push sleeve  210 , and the lower portion  220  of the push sleeve  210 , by the fluid, the force applied on the surface  305  of the ball  300  and the upper portion  215  of the push sleeve  210  will be greater than the pressure applied on the lower portion  220  of the push sleeve  210 . The resultant net force is in the direction of the lower end  190  of the expandable apparatus  100 , which when combined with the force of the compression spring  260  expanding, causes the push sleeve  210  to slide downward and retract the blades  101 ,  102 ,  103 . 
     As shown in  FIG. 6 , when it is desired to trigger the expandable apparatus  100  to re-extend the blades  101 ,  102 ,  103 , the drilling fluid flow is temporarily increased to, for example, at least double the pressure, until the ball  300  passes through the ball trap sleeve  225  into a screen catch  230 . In another embodiment, a second ball (not shown) may be dropped into the drill string to block the at least one fluid port  250  thereby increasing the pressure in the fluid passageway  192 . Because the ball  300  is formed of a malleable and/or compressible material, when the drilling fluid flow is increased, the pressure on the ball  300  may cause the ball  300  to deform or compress to a smaller size thus allowing the ball  300  to pass through the ball trap sleeve  225  into the screen catch  230 . With the ball  300  in the screen catch  230 , the fluid may travel unimpeded around the ball  300  out the screen catch  230 . Once the ball  300  is in the screen catch  230 , the drilling fluid flow may be reduced to the previous pressure. The resultant net force on the upper portion  215  of the push sleeve  210  and the lower portion  220  of the push sleeve  210  is in the direction of the upper end  191  of the expandable apparatus  100  and causes the push sleeve  210  to slide upward and extend the blades  101 ,  102 ,  103  as previously described in  FIG. 4 . The process of retracting and extending the blades  101 ,  102 ,  103  described in  FIGS. 4 through 6  may be repeated as desired until the screen catch  230  cannot hold any additional balls  300  expelled from the ball trap sleeve  225 . 
     Although the forgoing disclosure illustrates embodiments of an expandable apparatus comprising an expandable reamer apparatus, the disclosure should not be so limited. For example, in accordance with other embodiments of the disclosure, the expandable apparatus may comprise an expandable stabilizer, wherein the one or more expandable features may comprise stabilizer blocks (e.g., the cutter blocks  105 ,  106 ,  107  may be replaced with one or more stabilizer blocks). Thus, while certain embodiments have been described and shown in the accompanying drawings, such embodiments are merely illustrative and not restrictive of the scope of the invention, and this invention is not limited to the specific constructions and arrangements shown and described, since various other additions and modifications to, and deletions from, the described embodiments will be apparent to one of ordinary skill in the art. 
     While particular embodiments of the invention have been shown and described, numerous variations and other embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention only be limited in terms of the appended claims and their legal equivalents.

Summary:
Expandable reamers for enlarging boreholes in subterranean formations include a tubular body and at least one member positioned in openings in the tubular body. The at least one member is configured to move between retracted and extended positions. A push sleeve is disposed at least partially within the tubular body and coupled to the at least one member. The push sleeve moves axially upward to move the at least one member to the extended position in response to a pressure of drilling fluid passing through a drilling fluid flow path in the tubular body. The push sleeve moves axially downward to move the at least one member to the retracted position in response to a pressure of drilling fluid upon a restrictive element disposed within the fluid passageway. The restrictive element disposed within the fluid passageway may be discarded from the fluid passageway by increasing the flow rate through the drilling fluid flow path.