Patent Publication Number: US-2004055786-A1

Title: Positive displacement apparatus for selectively translating expander tool downhole

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to methods for wellbore completion. More particularly, the invention relates to an apparatus for selectively translating a completion tool, such as an expander tool, downhole.  
       [0003] 2. Description of the Related Art  
       [0004] Hydrocarbon and other wells are completed by forming a borehole in the earth and then lining the borehole with steel pipe or casing to form a wellbore. After a section of wellbore is formed by drilling, a section of casing is lowered into the wellbore and temporarily hung therein from the surface of the well. Using apparatus known in the art, the casing is cemented into the wellbore by circulating cement into the annular area defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.  
       [0005] It is common to employ more than one string of casing in a wellbore. In this respect, a first string of casing is set in the wellbore when the well is drilled to a first designated depth. The first string of casing is hung from the surface, and then cement is circulated into the annulus behind the casing. The well is then drilled to a second designated depth, and a second string of casing, or liner, is run into the well. The second string is set at a depth such that the upper portion of the second string of casing overlaps the lower portion of the first string of casing. The second liner string is then fixed or “hung” off of the existing casing by the use of slips which utilize slip members and cones to wedgingly fix the new string of liner in the wellbore. The second casing string is then cemented. This process is typically repeated with additional casing strings until the well has been drilled to total depth. In this manner, wells are typically formed with two or more strings of casing of an ever decreasing diameter.  
       [0006] Apparatus and methods are emerging that permit tubulars to be expanded in situ. The apparatus typically includes expander tools that are run into the wellbore on a working string. The expander tools include a plurality of expansion assemblies that are urged radially outward into contact with a tubular therearound. The expansion assemblies typically comprise a piston disposed within a recess of the expander tool body, and a roller member positioned on or above an external piston surface. In some arrangement&#39;s, the expansion assemblies are urged outward from the body of the expander tool by mechanical force. More commonly, the back surface of the expansion assembly is exposed to hydraulic pressure from within the bore of the tool. Fluid pressure is provided either by injecting fluid under pressure into the wellbore from the surface, or by activating a dedicated fluid reservoir associated with the tool.  
       [0007] As sufficient pressure is generated on the piston surface behind the expansion assemblies, the tubular being acted upon by the expander tool is expanded past its point of elastic deformation. In this manner, the inner and outer diameter of the tubular is increased in the wellbore. By rotating the expander tool in the wellbore and/or moving the expander tool axially in the wellbore with the expansion assemblies actuated, a tubular can be expanded into plastic deformation along a predetermined length in a wellbore.  
       [0008] Multiple uses for expandable tubulars are being discovered. For example, an intermediate string of casing can be hung off of a string of surface casing by expanding an upper portion of the intermediate string into frictional contact with the lower portion of surface casing therearound. This allows for the hanging of a string of casing without the need for a separate slip assembly as described above. Additional applications for the expansion of downhole tubulars exist, such as the use of an expandable sand screen.  
       [0009] There are problems associated with the expansion of tubulars. One problem particularly associated with the use of rotary expander tools is the likelihood of obtaining an uneven expansion of a tubular. In this respect, the inner diameter of the tubular that is expanded tends to initially assume the shape of the compliant rollers of the expander tool, including imperfections in the rollers. Moreover, as the working string is rotated from the surface, the expander tool may temporarily stick during expansion of a tubular, then turn quickly, and then stop again. This spring-type action in the working string further creates imperfections in the expansion job.  
       [0010] Another obstacle to smooth expansion relates to the phenomenon of pipe stretch. Those of ordinary skill in the art will understand that raising a working string a selected distance at the surface does not necessarily translate into the raising of a tool at the lower end of a working string by that same selected distance. The potential for pipe stretch is great during the process of expanding a tubular. Once the expander tool is actuated at a selected depth, an expanded profile is created within the expanded tubular. This profile creates an immediate obstacle to the raising or lowering of the expander tool. Merely raising the working string a few feet from the surface will not, in many instances, result in the raising of the expander tool; rather, it will only result in stretching of the working string. Applying further tensile force in order to unstick the expander tool may cause a sudden recoil, causing the expander tool to move uphole too quickly, leaving gaps in the tubular to be expanded.  
       [0011] The same problem exists in the context of pipe compression. In this respect, the lowering of the working string from the surface does not typically result in a reciprocal lowering of the expander tool at the bottom of the hole. This problem is exacerbated by pipe drag caused by friction between the drill pipe and the casing. Because of pipe drag, it is not known how much weight is actually reaching the tools down hole. The overall result of these drag problems is that the inner diameter of the expanded tubular may not have a uniform circumference along the desired length.  
       [0012] There is a need, therefore, for an improved apparatus for expanding a portion of casing or other tubular within a wellbore. Further, there is a need for an apparatus which will aid in the expansion of a tubular downhole and which reduces the potential of pipe-stretch/pipe-compression by the working string. Correspondingly, there is a need for a method for expanding a tubular which avoids the risk of uneven expansion of the tubular caused by pipe-stretch incident to raising the working string. Still further, a need exists for an apparatus which will selectively translate a completion tool such as a rotary expander tool axially downhole without requiring that the working string be raised or lowered.  
       [0013] There is yet a further need for an apparatus which translates a rotary expander tool by means of a piston selectively driven through positive displacement.  
       SUMMARY OF THE INVENTION  
       [0014] The present invention provides an apparatus and method for selectively translating a completion tool, such as an expander tool, downhole. According to the present invention, a translation apparatus is introduced into a wellbore. The translation apparatus is lowered downhole on a working string along with an expander tool, and along with a lower string of casing or other tubular to be expanded. The expander tool includes compliant rollers which are expandable radially outward against the inner surface of the tubular upon actuation.  
       [0015] The translation apparatus of the present invention utilizes positive displacement to translate the expander tool. The positive displacement translation apparatus first defines a set of three essentially concentric tubular members which reside below the expander tool. The three concentric tubulars represent (1) an outer sleeve, (2) an inner mandrel, and (3) a middle displacement piston nested between the sleeve and the mandrel. These three tubular members are disposed within the expandable liner or other tubular to be expanded.  
       [0016] A fluid transfer chamber is provided below the middle displacement piston. Rotation of the positive displacement apparatus serves to draw fluid into the fluid transfer chamber. This fluid is applied against the base of the displacement piston in order to force the displacement piston upward between the outer sleeve and the inner mandrel. This, in turn, causes the displacement piston to act against the rotary expander tool. In this manner, the displacement piston translates the expander tool incrementally upward within the wellbore.  
       [0017] In order to fill the fluid transfer chamber with fluid, a positive displacement mechanism is provided. First, a stator member is provided below the middle displacement piston. The stator member has a top face at its top end configured in a wave form. In one aspect, the wave form is sinusoidal. At the same time, a rotor piston is provided below the displacement piston. The rotor piston has a bottom face which rides upon the wave form face of the stator member. Preferably, the bottom face of the rotor piston also has a sinusoidal wave form shape. Rotation of the expander tool and the positive displacement apparatus, including the rotor piston, serves to reciprocate the rotor piston in an up-and-down manner. By this reciprocating motion, fluid is drawn into the fluid transfer chamber and fed against the base of the displacement piston. This, in turn, causes the expander tool to be translated upwardly within the wellbore. In this manner, the expander tool can be raised without raising the working string itself. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0018] So that the manner in which the above recited features of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
     [0019]FIG. 1 is a cross-sectional view of a wellbore having an upper string of casing, and a lower string of casing being lowered into the upper string of casing. In this view, the lower string of casing serves as the expandable tubular. Also depicted in FIG. 1 is a positive displacement apparatus of the present invention for translating an expander tool.  
     [0020]FIG. 2 is a more detailed view of a scribe as might be placed in the lower string of casing. The scribe serves as a point of structural weakness in the lower string of casing, permitting severance upon expansion of the casing.  
     [0021]FIG. 3 is an enlarged view of the fluid transfer chamber in an exemplary positive displacement apparatus of the present invention.  
     [0022]FIG. 4 is a cross-sectional view of a positive displacement apparatus of the present invention, taken across line  4 - 4  of FIG. 1.  
     [0023]FIG. 5 is a cross-sectional view of the positive displacement apparatus of FIG. 1. In this view, oil is being transferred from the fluid transfer chamber, up the transfer chamber channel, and into the piston feed channel. Visible in this view is the initial translation of the middle displacement piston.  
     [0024]FIG. 6 presents an exploded view of an expander tool as might be translated by the positive displacement pump/piston apparatus of the present invention.  
     [0025]FIG. 7 presents a portion of the expander tool of FIG. 5 in cross-section, with the view taken across line  7 - 7  of FIG. 6.  
     [0026]FIG. 8 depicts the wellbore of FIG. 1. In this view, the expander tool has been actuated so as to begin expanding the lower string of casing. Further, the torque anchor has been actuated so as to stabilize the lower string of casing and to prevent rotational movement during expansion.  
     [0027]FIG. 9 depicts the wellbore of FIG. 8. In this view, the expander tool remains actuated by hydraulic pressure from the surface. The working string has been rotated so as to begin raising the expander tool within the wellbore. In this respect, rotation of the positive displacement apparatus serves to actuate the piston within the apparatus. This in turn, causes the expander tool to be translated co-axially within the wellbore.  
     [0028]FIG. 10 depicts the wellbore of FIG. 9. Here, the expander tool has been raised further within the wellbore so as to expand the lower string of casing into the surrounding upper string of casing along a desired length. The portion of the lower string of casing having a scribe has been expanded, causing severance of the lower string of casing.  
     [0029]FIG. 11 is a sectional view of the wellbore of FIG. 10. In this view, the torque anchor and the expander tool have been de-actuated and the lower collet has been released from the liner. Also, the expansion assembly is being removed from the wellbore. Removal of the expansion assembly brings with it the severed upper portion of the lower casing string.  
     [0030]FIG. 12 is a sectional view of the wellbore of FIG. 11, with the positive displacement apparatus of the present invention having been removed. In this view, the lower string of casing has been expanded into frictional and sealing engagement with the upper string of casing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0031]FIG. 1 presents a cross-sectional view of a wellbore  100  having an upper string of casing  110  and a lower string of casing  120 . The lower string of casing  120 , or liner, is being lowered into the wellbore  100  co-axially with the upper string of casing  110 . The lower string of casing  120  is positioned such that an upper expandable portion  120 E of the lower string of casing  120  overlaps with a lower portion  110 L of the upper string of casing  110 .  
     [0032] In the example of FIG. 1, the lower string of casing  120  serves as an expandable tubular. The lower string of casing  120  will be hung off of the upper string of casing  110  by expanding an upper portion  120 E of the lower string of casing  110  into the lower portion  110 L of the upper string of casing  110 . However, it is understood that the apparatus and method of the present invention may be utilized to expand downhole tubulars other than strings of casing.  
     [0033] A sealing member  222  is preferably disposed on the outer surface of the lower string of casing  120 . In one embodiment, the sealing member  222  defines a matrix formed in grooves (not shown) on the outer surface of the lower string of casing  120 . However, other configurations are permissible, including one or more simple rings formed circumferentially around the lower string of casing  120 . In the arrangements of FIG. 1, a single ring  222  is shown.  
     [0034] The sealing member  222  is fabricated from a suitable material based upon the service environment that exists within the wellbore  100 . Factors to be considered when selecting a suitable sealing member  222  include the chemicals likely to contact the sealing member, the prolonged impact of hydrocarbon contact on the sealing member, the presence and concentration of erosive compounds such as hydrogen sulfide or chlorine, and the pressure and temperature at which the sealing member must operate. In a preferred embodiment, the sealing member  222  is fabricated from an elastomeric material. However, non-elastomeric materials or polymers may be employed as well, so long as they substantially prevent production fluids from passing upwardly between the outer surface of the lower string of casing  120 L and the inner surface of the upper string of casing  110 L after the expandable section  120 L of the casing  120  has been expanded.  
     [0035] Also positioned on the outer surface of the lower string of casing  120  is at least one slip member  224 . The slip member  224  is used to provide an improved grip between the expandable tubular  120 E and the upper string of casing  110 L when the lower string of casing  120  is expanded. In this example, the slip member  224  defines a plurality of carbide buttons interspersed within the matrix of the sealing member  222 . However, any suitable placement of a hardened material which provides a gripping means for the lower string of casing  120  into the upper string of casing  110  may be used. For example, a simple pair of rings having grip surfaces (not shown) formed thereon for engaging the inner surface of the upper string of casing  110  when the lower string of casing  120  is expanded would be suitable. The size, shape and hardness of the slips  224  are selected depending upon factors well known in the art such as the hardness of the inner wall of casing  110 , the weight of the casing string  120  being hung, and the arrangement of slips  224  used.  
     [0036] In order to expand the lower string of casing  120  seen in FIG. 1, an expander tool  400  is provided. An expander tool as might be used in the expansion assembly is seen more fully in FIG. 6. FIG. 6 is an exploded view of an exemplary expander tool  400 . FIG. 7 presents the same expander tool  400  in cross-section, with the view taken across line  7 - 7  of FIG. 6.  
     [0037] The expander tool  400  has a body  402  which is hollow and generally tubular. The central body  402  has a plurality of recesses  414  to hold a respective roller  416 . Each of the recesses  414  has parallel sides and holds a respective piston  420 . The pistons  420  are radially slidable, one piston  420  being slidably sealed within each recess  414 . The back side of each piston  420  is exposed to the pressure of fluid within the hollow bore  415  of the tool  400 . In this manner, pressurized fluid provided from the surface of the well can actuate the pistons  420  and cause them to extend outwardly whereby the rollers  416  contact the inner surface of the tubular  120 L to be expanded.  
     [0038] It is understood that the expander tool  400  shown in the referenced illustrations is merely exemplary. Any arrangement for an expander tool may be employed with the translation apparatus of the present invention  100 . These include not only hydraulic expander tools, but mechanically activated expander tools as well. Further, the utility of the present invention is not limited to hydraulical expander tools that rely upon hydraulic pressure from the surface, but includes hydraulic expander tools that utilize a dedicated fluid reservoir associated with the tool. For example, a sealed fluid reservoir may be provided between concentric tubulars downhole. Fluid from this reservoir may be applied against the expansion assemblies within an expander tool, thereby urging them outwardly to expand a surrounding tubular. Alternatively, a blended system may be adopted having a mechanically advanced piston or other roller carrier that rides on a ramp, and has a hydraulic assist.  
     [0039] Disposed within each piston  420  is a roller  416 . In one embodiment of the expander tool  400 , rollers  416  are near-cylindrical and slightly barreled. Each of the rollers  416  is supported by a shaft  418  at each end of the respective roller  416  for rotation about a respective rotational axis. The rollers  416  are preferably tilted at a very slight angle of approximately two degrees relative to the longitudinal axis of the tool  400 . This aids in translation of the expander tool upward. In the arrangement of FIG. 6, the plurality of rollers  416  are radially offset at mutual 120-degree circumferential separations around the central body  402 . In the arrangement shown in FIG. 6, only a single row of rollers  416  is employed. However, additional rows may be incorporated into the body  402 , as shown in FIG. 1.  
     [0040] The rollers  416  illustrated in FIG. 6 have generally cylindrical or barrel-shaped cross sections; however, it is to be appreciated that other roller shapes are possible. For example, the roller  416  may have a cross sectional shape that is conical, truncated conical, semi-spherical, multifaceted, elliptical or any other cross sectional shape suited to the expansion operation to be conducted within the tubular  120 . In addition, at least one portion of the roller surface is preferably tapered. In some instances, solid pads will take the place of rollers in an assembly.  
     [0041] The expander tool  400  is preferably designed for use at or near the end of a working string  170 . In the arrangement of FIG. 1, connection between the working string  170  and the expander tool  400  is by a mandrel  340 ′. The mandrel  340 ′ defines an elongated tubular body that extends into and through the expander tool  400 . The mandrel portion above the expander tool  400  is shown at  340 ′, while the mandrel portion below the expander tool is shown at  340 . The upper mandrel  340 ′ includes a spline  337  which is received within a profile (not shown) within the expander tool body  402 . In this way, rotation of the working string  170  and the upper mandrel  340 ′ imparts rotation to the expander tool  400 . At the same time, and as will be described below, the upper mandrel  340 ′ is able to radially receive the expander tool  400  when the tool  400  is translated upward by a positive displacement apparatus  300 .  
     [0042] In order to actuate the exemplary expander tool  400  of FIG. 6, fluid is injected into the working string  170 . Fluid under pressure then travels downhole through the working string  170  and into the perforated tubular bore  415  of the tool  400 . From there, fluid contacts the backs of the pistons  420 . As hydraulic pressure is increased, fluid forces the pistons  420  outwardly from their respective recesses  414 . This, in turn, causes the rollers  416  to make contact with the inner surface of the liner  120 L. Fluid finally exits the expander tool  400  through the mandrel  340  at the base of the tool  400 . The circulation of fluids to and within the expander tool  400  is preferably regulated so that the contact between and the force applied to the inner wall of the liner  120 E is controlled. The pressurized fluid causes the piston assembly  420  to extend radially to place the rollers  416  into contact with the inner surface of the lower string of casing  120 E. With a predetermined amount of fluid pressure acting on the piston surface  420 , the lower string of expandable liner  120 E is expanded past its elastic limits. Of course, as noted previously, other means for activating the pistons of the expander tool may be employed.  
     [0043] In the arrangement of FIG. 1, the lower end of the expander tool  400  is connected to a positive displacement apparatus  300 . The positive displacement apparatus  300  generally defines a tubular assembly which is able to translate the expander tool  400  upwardly in the wellbore  100  when the expander tool  400  and the positive displacement apparatus  300  are rotated.  
     [0044] In the arrangement shown in FIG. 1, the positive displacement apparatus  300  first comprises a set of three essentially concentric tubular members which reside below the expander tool  400 . The three tubulars represent (1) an outer sleeve  330 , (2) an inner mandrel  340 , and (3) a middle displacement piston  355  nested between the sleeve  330  and the mandrel  340 . These three tubular members  330 ,  355 ,  340  are disposed proximate the expandable liner  120  or other tubular to be expanded. Hence, four separate tubulars  120 ,  340 ,  355 ,  330  are disposed essentially concentrically within the upper casing string  100 .  
     [0045]FIG. 4 is a cross-sectional view of a positive displacement apparatus  300  of the present invention, taken across line  4 - 4  of FIG. 1. The relative placement of the liner string  120  and of the three tubulars  340 ,  355 ,  330  of the present invention is seen more fully in this view. It can be seen that an annular region is formed between the inner mandrel  340  and the displacement piston  355 . Likewise, an annular region is found between the displacement piston  355  and the outer sleeve  330 . Also, an annular region is created between the sleeve  330  and the liner string  120 . Finally, a hollow bore  345  is defined within the inner mandrel  340 .  
     [0046] Each of the three tubulars  340 ,  355 ,  330  of the positive displacement apparatus  300  has an upper end and a lower end. The upper end of the displacement piston  355  is connected to the expander tool  400 . Connection is preferably by a threaded connection.  
     [0047] In order to impart rotation to the expander tool  400 , and as noted above, a splined connection  337  is provided between the upper mandrel  340 ′ and the expander tool body  402 . The splined connection  337  is in the nature of a traveling spline.  
     [0048] A fluid transfer chamber  348  is provided below the displacement piston  355 . The fluid transfer chamber  348  and its related components are seen more fully in the enlarged view of FIG. 3. As shown, the fluid transfer chamber  348  is defined by the inner mandrel  340  on the inside, and by a fluid transfer chamber housing  346  on the outside. The purpose of the fluid transfer chamber  348  is to serve as a reservoir through which oil may be transferred from the annular space  325  (shown in FIG. 4) outside of the sleeve  330  to the base of the displacement piston  355 , thereby fluidly forcing the displacement piston  355  upward. The annulus  325  is loaded with a clean, lightweight liquid medium such as oil. A cement bushing (not shown) positioned at a lower end of the positive displacement apparatus  300  supports the column of fluid outside of the sleeve  330  and within the liner  120 . As seen in FIG. 3, the fluid transfer chamber  348  is placed in fluid communication with the annulus  325  by means of an annular feed channel  324 . The annular feed channel  324  has a through-opening  324 ′ at one end which is in open communication with the annulus  325 . At its opposite end, the annular feed channel  324  has a check valve opening  324 ″ which delivers oil to an inflow check valve  374 .  
     [0049] The inflow check valve  374  permits oil to flow into the fluid transfer chamber  348 , but does not permit oil to flow out of the fluid transfer chamber  348 . In the arrangement shown in FIG. 3, the inflow check valve  374  is a bullet nose check valve. However, any suitable one-way valve may be used.  
     [0050] As shown in FIG. 3, more than one check valve is employed for the positive displacement apparatus  300 . In addition to the inflow check valve  374 , an outflow check valve  372  is also provided. As with the inflow check valve  374 , the outflow check valve  372  is a one-way check valve. However, the outflow check valve  372  permits oil to flow out of the fluid transfer chamber  348 , but does not permit oil to flow into the fluid transfer chamber  348 . In the arrangement shown in FIG. 3, the inflow check valve  372  is a bullet nose check valve. However, any suitable one-way valve may be used, or none at all. As oil is delivered through the inflow check valve  374 , the fluid transfer chamber  348  is filled. As additional oil is pumped into the fluid transfer chamber  348 , pressure is created therein. Ultimately, oil is forced out of the fluid transfer chamber  348  through the outflow check valve  372 . Oil flows from the outflow check valve  372  and into a piston feed channel  334 . This oil, in turn, provides a force against the lower end of the middle displacement piston  355 , forcing it upward with respect to the outer sleeve  330  and the inner mandrel  340 . Because the displacement piston  355  is connected to the lower end of the expander tool  400 , upward displacement of the displacement piston  355  translates the expander tool  400  upward within the expandable tubular  120 E.  
     [0051] The arrangement of FIG. 3 also presents a transfer chamber channel  364 . The transfer chamber channel  364  provides a path of fluid communication between the check valves  374  and  372 , and the fluid transfer chamber  348  itself. In this arrangement, the transfer chamber channel  364  resides within a fluid transfer channel housing  365 . The fluid transfer channel housing  365  defines the top of the fluid transfer chamber  348 , and also houses the check valves  374  and  372 . It is understood, however, that other arrangements may be provided for channeling fluid from the fluid transfer chamber  348 , through the outflow check valve  372 , and against the displacement piston  355 .  
     [0052] A means is needed to draw oil from the annular space  325  into the fluid transfer chamber  348 . In the present invention, the drawing of oil is accomplished through positive displacement. In accordance with the present invention, a stator member  210  is first provided. The stator member  210 , in one aspect, defines a tubular body which is disposed below the fluid transfer chamber  348 . The stator member  210  has a top surface which serves as a face  385 . The face  385  is configured in a wave form. Preferably, the wave form is sinusoidal. The stator member  210  remains stationary, while the mandrel  340 ′ rotates through it.  
     [0053] As seen in FIG. 1, a lower portion of the mandrel  340 ″ extends below the stator  210 . This lower mandrel  340 ″ also rotates in response to rotation imparted by the working string  170 . A swivel, shown schematically as a sub at  150 , is positioned between the lower mandrel  340 ″ and the collet  160  to further facilitate rotation of the inner mandrel  340  and the lower mandrel  340 ″.  
     [0054] Fixed between the fluid transfer chamber  348  and the tubular body  210  is a rotor piston  357 . The rotor piston  357  is rotated as part of the positive displacement apparatus  300 . In this respect, a key or other splined-type connection  335  connects the mandrel  340  to the rotor piston  357  to impart rotation to the rotor piston  357 . In the arrangement of FIG. 3, the fluid transfer channel housing  365  also includes separate split rings  332  and  362  which provide a locating shoulder between the outer sleeve  330 , the fluid transfer channel housing  365 , and the inner mandrel  340 . These split rings  332 ,  362  ensure that the components of the positive displacement apparatus  300  remain axially stationary relative to the rotor piston  357 . It is understood, however, that the present invention is not limited to any particular manner in which the rotor piston  357  is connected to the positive displacement apparatus  300 , so long as the rotor piston  357  is able to reciprocate in response to the wave form on the face  385  of the stator member  210 .  
     [0055] The rotor piston  357  has an upper end which defines the bottom of the fluid transfer chamber  348 . The rotor piston  357  further has a lower end that includes a face  380  configured in a wave form similar to the face  385  on the tubular body  210 . The face  380  of the rotor piston  357  rides upon the face  385  of the stator member  210  as the rotor piston  357  is rotated. Preferably, the rotor piston face  380  and the stator member face  385  are each sinusoidal, though other wave forms may be used. This means that rotation of the rotor piston  357  by 90 degrees creates a single stroke length. In the preferred arrangement, the stroke length is approximately one-half inch (1.27 cm). Thus, rotation of the expander tool  400  and the positive displacement apparatus  300 , including the rotor piston  357 , serves to reciprocate the rotor piston  357  in an up-and-down manner along a stroke length of approximately one-half of an inch. As will be shown, it is this reciprocating stroke that produces the positive displacement used to translate the expander tool  400 .  
     [0056] As noted, the positive displacement apparatus  300  includes a fluid transfer chamber  348 . The fluid transfer chamber  348  is sized and configured such that reciprocal movement of the rotor piston  357  causes translational movement of the displacement piston  355 . During the first half of the stroke cycle, the rotor piston  357  moves upwards, thereby reducing the volume of the fluid transfer chamber  348 . Reduction of the volume of the fluid transfer chamber  348  extrudes oil from the fluid transfer chamber  348  and into the piston feed channel  334 . This injection of oil moves the displacement piston  355  upward within the expandable tubular  120 E.  
     [0057] A biasing member  342  is housed inside the fluid transfer chamber  348 . The biasing member  342  biases the rotor piston  357  in its downward position to ensure essentially continuous contact between the bottom face  380  of the rotor piston  357  and the top face  385  of the stator member  210 . Preferably, the biasing member  342  is a spring. The spring  342  becomes compressed during the first half of the stroke cycle when the rotor piston  357  is thrust upward. During the second half of the rotor piston&#39;s  357  stroke cycle, the rotor piston  357  moves back into phase with the face  385  of the stator member  210 . The spring  342  pushes the rotor piston  357  back downward, re-expanding the volume of the fluid transfer chamber  348 . The second half of the stroke cycle occurs after an additional  90  degree rotation of the rotor piston  357 . This movement downward of the rotor piston  357  creates a vacuum within the fluid transfer chamber  348 , thereby drawing fluid, e.g., oil, into the chamber  348  from the piston-sleeve annulus  325 . With continued cycles, the transfer chamber  348  becomes filled with fluid under pressure. Ultimately, the oil is extruded out of the transfer chamber  348  and against the base of the displacement piston  355 .  
     [0058]FIG. 5 presents a cross-sectional view of the positive displacement apparatus  300  of FIG. 1. In this view, oil is being transferred from the fluid transfer chamber  348 , up the transfer chamber channel  364 , and into the piston feed channel  334 . Visible in this view is the initial translation of the middle displacement piston  355 . Continued rotation of the positive displacement apparatus  300  will raise the displacement piston  355  further within the expandable tubular  120 E. This, in turn, causes the expander tool  400  to be translated upwardly. In this manner, the expander tool  400  can be raised without raising the working string  170  itself.  
     [0059] In order to effectuate the transfer of oil from the annulus  325 , into the fluid transfer chamber  348 , and against the displacement piston  355 , it is desirable to utilize various seals between the components of the positive displacement apparatus  300 . FIG. 5 presents a variety of seals. These include a first sealing member  356  at the lower end of the displacement piston  355 . The sealing member  356  creates a fluid seal between the displacement piston  355  and the tubulars  330 ,  340 , thereby allowing all the fluid in the piston feed channel  334  to fully act upon the displacement piston  355 . A second sealing member  359  is disposed at the lower end of the transfer channel housing  365 . The second sealing member  359  creates a fluid tight seal for the transfer channel housing  365  between the transfer chamber housing  346  and the mandrel  340 , thereby preventing a leakage from the upper end of the fluid transfer chamber  348 . A third sealing member  358  is disposed at the upper end of the rotor piston  357 . The sealing member  358  creates a fluid tight seal for the rotor piston  357  housed between the transfer chamber housing  346  and the mandrel  340 , thereby preventing any fluid leakage from the lower end of the fluid transfer chamber  348 .  
     [0060] Seals are additionally positioned inside and outside of the outer sleeve  330  at the lower end. First, seal  337  seals the interface between the outer sleeve  330  and the inner mandrel  340 . Second, seal  353  seals the annular area between the outer sleeve  330  and the fluid transfer channel housing  365 . These seals  337 ,  353  assist in maintaining fluid within the annular feed channel  324  during the translation process. The seals  337 ,  353  are seen in FIGS. 3 and 5.  
     [0061] The present invention is not limited in scope to any single arrangement of seals. In this respect, various means are known for providing a fluid seal between nested tubulars. Any sealing arrangement may be utilized, so long as the reciprocation of the rotor piston  357  within the fluid transfer chamber  348  is able to draw oil in during a first stroke, and extrude oil during an opposite second stroke. In the arrangement shown in FIGS. 3 and 5, oil is drawn into the fluid transfer chamber  348  on the downstroke, and extruded during the upstroke. Of course, the apparatus  300  can also be configured to draw oil on the upstroke and to discharge on the downstroke.  
     [0062] In operation, the positive displacement apparatus  300  of the present invention is run into the wellbore  100  on the lower end of the working string  170 . As seen in FIG. 1, the positive displacement apparatus  300  is connected to the expander tool  400  at one end. In the arrangement shown in FIG. 1, the apparatus  300  is connected to the bottom of the expander tool  400 . However, it will be appreciated that the positive displacement apparatus  300  will also function if the positive displacement apparatus  300  is above the expander tool  400 . In this regard, the check valves  374 ,  372  and associated chamber  348  and channel  364  would be positioned above the displacement piston  355 .  
     [0063] In order to accomplish the expansion operation in a single trip, the working string  170  also is temporarily connected to the lower string of casing  120 . In this manner, the lower string of casing  120  can be introduced into the wellbore  100  at the same time as the expander tool  400  and the apparatus  300 . In FIG. 1, a collet  160  is presented as the releasable connection. The collet  160  is shown near the end of the working string  170 . The collet  160  is landed into a radial profile  165  within the lower string of casing  120  so as to support the lower string of casing  120 . The collet  160  is mechanically or hydraulically actuated as is known in the art, and supports the lower string of casing  120  until such time as the lower string of casing  120  has been expandably set by actuation of the expander tool  400 .  
     [0064]FIG. 8 depicts the wellbore of FIG. 1, in which the expander tool  400  has been actuated. It can be seen that an initial portion of the lower string of casing  120  has been expanded. As explained above, actuation of the expander tool  400  is by injection of fluid under pressure into the working string  170 . Fluid travels from the surface, down the working string  170 , and through the bore  415  of the expander tool  400 .  
     [0065]FIG. 9 depicts the wellbore  100  of FIG. 8. In this view, the expander tool  400  remains actuated. This allows the expander tool  400  to move within the expandable tube  120 E relative to the running tool collet  160 . Also, in FIG. 9, the working string  170  has been rotated so as to begin raising the expander tool  400  within the expandable tubular  120 E. As described above, rotation of the working string  170  causes the displacement piston  355  and, therewith, the expander tool  400  to be translated axially within the wellbore  100 . FIG. 9 thus demonstrates the expander tool  400  being raised within the expandable tubular  120 E by actuation of the positive displacement apparatus  300 .  
     [0066] It is contemplated in FIG. 1 that rotation of the rotor piston  357  and of the expander tool  400  is accomplished by rotating the working string, i.e., drill pipe  170 , from the surface. However, rotation may also be achieved by activation of a downhole rotary motor, such as a mud motor (not shown).  
     [0067]FIG. 10 depicts the wellbore  100  of FIG. 9. Here, the actuated expander tool  400  has been raised further within the wellbore  100  so as to expand the lower string of casing  120  into the surrounding upper string of casing  110  along a desired length. This, in turn, results in an effective hanging and sealing of the lower string of casing  120  upon the upper string of casing  110  within the wellbore  100 . Thus, the apparatus  300  enables a lower string of casing  120  to be hung onto an upper string of casing  110  by expanding the lower string  120  into the upper string  110 , and without raising or lowering the working string  170  from the surface during expansion operations. It is understood, however, that the working string  170  may optionally be raised and lowered while the expander tool  400  is still actuated and after the initial expansion has taken place, i.e., after the expander tool  400  has been initially actuated. Using this procedure, the collet  160  would first need to be released from the liner  120 .  
     [0068] Following expansion operations, hydraulic pressure from the surface is relieved, allowing the pistons  420  to return to the recesses  414  within the body  402  of the tool  400 . The expander tool  400  and the positive displacement apparatus  300  can then be withdrawn from the wellbore  100  by pulling the run-in tubular  170 . FIG. 11 is a partial section view of the wellbore  100  of FIG. 10. In this view, the expander tool  400  has been de-actuated and is being removed from the wellbore  100  along with the positive displacement apparatus  300 . In addition, the collet  160  or other releasable connection must be released from the liner  120 , as shown in FIG. 11.  
     [0069] In one procedure for utilizing the positive displacement apparatus  300  of the present invention, the liner  120  is expanded to its top end. However, the length of expansion is discretionary. An upper non-expanded portion  120 S of the liner  120  can be severed after a portion  120 E is expanded. The severed portion  120 S of the lower string of casing  120  above the expander tool  400  must then be removed from the wellbore  100 . To accomplish this, typical casing severance operations may be conducted. This would be done via a subsequent trip into the wellbore  100 . However, as an alternative shown in FIG. 11, the severed portion  120 S of the lower string of casing  120  may be removed from the wellbore  100  at the same time as the expander tool  400  after the collet  160  has been released from the liner  120 . In order to employ this method, a novel scribe  130  is formed on the outer surface of the lower string of casing  120 .  
     [0070] An enlarged view of the scribe  130  in one embodiment is shown in FIG. 2. The scribe  130  defines a cut made into the outer surface of the lower string of casing  120 . The scribe  130  is preferably placed around the casing  120  circumferentially. The depth of the scribe  130  needed to cause the break is dependent upon a variety of factors, including the tensile strength of the tubular, the overall deflection of the material as it is expanded, the profile of the cut, and the weight of the tubular being hung. The scribe  130  must be shallow enough that the tensile strength of the tubular  120  supports the weight below the scribe  130  during run-in. The arrangement shown in FIG. 2 employs a single scribe  130  having a V-shaped profile so as to impart a high stress concentration onto the casing wall. However, other profiles may be employed.  
     [0071] The scribe  130  creates an area of structural weakness within the lower casing string  120 . When the lower string of casing  120  is expanded at the depth of the scribe  130 , the lower string of casing  120  is cleanly severed. The severed portion  120 U of the lower casing string  120  can then be easily removed from the wellbore  100 . Thus, the scribe  130  may serve as a release mechanism for the lower casing string  120 . Other means for severing the tubular  120  upon expansion may be developed as well.  
     [0072] In order to remove the severed portion  120 S of the lower string of casing  120  from the wellbore  100 , a second connection must be provided with the severed portion of the lower string of casing  120 . In the arrangement of FIGS.  8 - 11 , a releasable connector  124  is shown. The connector  124  is demonstrated as a collet  124  to be landed into a radial profile  125  within the lower string of casing  120 . The collet  124  is mechanically or pneumatically actuated as is known in the art, and supports the severed portion  120 S of the lower string of casing  120  while the apparatus  300  and the expander tool  400  are being removed from the wellbore  100 . Removal of the working string  170  with the expander tool  400  brings with it the severed portion  120 S of the lower casing string  120 . It is, of course, understood that other means may be employed for removing a non-expanded upper portion of liner  120 , and that the arrangement shown in FIGS.  8 - 11  is purely exemplary.  
     [0073]FIG. 12 is a partial section view of the wellbore  100  of FIG. 11. In this view, the positive displacement apparatus  300  of the present invention and the expander tool  400  have been removed. It can be seen that the expandable portion  120 E of the lower string of casing  120  has been expanded into frictional and sealing engagement with the upper string of casing  110 . The seal member  222  and the slip member  224  are engaged to the inner surface of the upper string of casing  110 . Further, the annulus  135  between the lower string of casing  120  and the upper string of casing  110  has been optionally filled with cement, excepting that portion of the annulus which has been removed by expansion of the lower string of casing  120 E.  
     [0074] As a further aid in the expansion of the lower casing string  120 , a torque anchor  200  may optionally be utilized. The torque anchor  200  serves to prevent rotation of the stator  210  during the expansion process. The torque anchor  200  shown in FIG. 1 includes radially extendable cleating mechanism  240  for engaging the inner surface of the casing  110 . The torque anchor  200  is actuated during initial expansion of the expandable portion  120 E of the liner  120 . The torque anchor  200  may be released after initial expansion, as shown in FIG. 11.  
     [0075] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.