You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims benefit of Great Britain patent application serial number 0304335.3, filed Feb. 26, 2003, which is herein incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to tubing expansion, and in particular to the expansion of downhole tubing, and to tools and apparatus for use in expanding downhole tubing.  
           [0004]    2. Description of the Related Art  
           [0005]    A recent significant development in the oil and gas exploration and production industry has been the introduction of expandable downhole tubing, that is bore-lining tubing that is run into a drilled bore and then expanded to a larger diameter. This has permitted the creation of monobore or near monobore wells, that is wells having a substantially constant diameter. This may be achieved by running a tubular through existing bore-lining casing and into a section of open or unlined bore below the casing, but with the upper end of the new tubular overlapping the lower end of the existing casing. The tubular is then expanded to the same internal diameter as the existing casing.  
           [0006]    The new tubular is normally hung off the lower end of the existing casing, and to achieve pressure integrity it is also necessary that a seal is created between the overlapping ends of the casing and the tubular. Furthermore, the annulus between the tubular and the wall of the bore is normally filled and sealed with cement. Numerous proposals have been put forward for apparatus and methods for implementing this complex procedure, however difficulties remain in achieving a satisfactory solution to a number of problems, in particular in hanging the tubular off the casing, cementing the tubular, and sealing the tubular to the casing.  
           [0007]    Many of the principles utilized in the creation of a monobore and near monobore well have also been proposed for use in selected aspects of other, more conventional forms of well completion. For example, the use of expandable liner sections has been proposed to replace conventional liner hangers, where an upper end of a liner section is expanded to create a fluid-tight hanging support from the lower end of existing casing. However, the difficulties relating to providing adequate hanging support, sealing and cementing remain.  
           [0008]    The applicant has addressed a number of these difficulties in its earlier UK Patent Application GB0210256.4, the disclosure of which is incorporated herein by reference. This application describes provision of a tubular, in particular a liner, having a profiled section which is initially located below the lower end of the casing. The profiled liner section is expanded to an external diameter slightly larger than the internal diameter of the casing and the liner is then pulled back to locate the expanded profiled section within the lower end of the casing. The expanded profiled section and the casing interact, primarily by elastic deformation of the expanded profiled section, to create a temporary hanger. The profiling of the liner section is such that fluid may pass between the overlapping sections of the liner and casing, facilitating cementing the liner. The liner may then be further expanded to create a fluid-tight seal and permanent hanging support.  
           [0009]    Certain embodiments of the present invention relate to apparatus for use in similar operations. One embodiment of the invention relates to creation of a temporary hanger in a similar manner to that described in GB0210256.4, and further expanding the remainder of the liner below the hanger.  
         SUMMARY OF THE INVENTION  
         [0010]    According to a first aspect of the present invention there is provided a tubing expansion tool, the tool comprising:  
           [0011]    a mandrel defining at least one arcuate support surface having a radius of curvature; and  
           [0012]    at least one expansion member defining an arcuate bearing surface for contact with the support surface and having a radius of curvature corresponding to the radius of curvature of the mandrel support surface,  
           [0013]    the member being movable relative to the mandrel whereby the surfaces are in contact and movable over one another to move the expansion member from a smaller diameter first configuration towards a larger diameter second configuration.  
           [0014]    In aspects of the invention the objects of the invention may be realized by provision of curved contacting surfaces which are not necessarily arcuate or of constant radii. However, the provision of contacting surfaces of corresponding radii ensure that the area of contact between the surfaces remains relatively large between the first and second configurations. This is particularly useful where the expansion member is intended to expand tubing as the member moves from the first configuration to the second configuration, and thus experiences an expansion load at intermediate configurations in addition to the maximum diameter second configuration. This is in contrast to arrangements in which cooperating support and bearing surfaces define straight surfaces, for example corresponding conical surfaces where, while a relatively large area contact may be achieved at the largest diameter configuration, at intermediate configurations the bearing surface would only be supported at its ends, and thus the loaded expansion member would experience elevated bending stresses, making failure more likely. With preferred embodiments of the present invention, the expansion member will only experience compression, as the member is supported over at least a significant portion of its length, and thus will be able to withstand and exert far greater expansion forces.  
           [0015]    The enhanced ability of the tool to accommodate expansion loads at intermediate configurations provides a number of significant advantages, one being that the tool may be run into a bore in a smaller diameter configuration and accommodated within smaller diameter tubing, and indeed may be accommodated within the tubing which the tool is intended to expand. This contrasts with comparable conventional tools, which must be accommodated within an upset section of tubing, larger than the diameter of the tubing to be expanded, or even outside the tubing, thus limiting the minimum diameter of restriction which a tool string incorporating the tool may pass through. Thus, aspects of the invention also relates to an assembly in which the tool is located within tubing to be expanded, and to a method of expanding tubing from a first diameter to a second diameter in which at least an initial expansion of the tubing is achieved by moving an expansion member from a first configuration to a second configuration within the tubing. Of course in other aspects of the invention the expansion member may be moved from the first configuration to a second configuration externally of tubing to be expanded, and then subsequently located in the tubing to be expanded.  
           [0016]    Preferably, the support surface is convex and the bearing surface is concave, although in alternative embodiments the support surface may be concave and the bearing surface convex. Most preferably, the convex support surface is arranged such that the radial extent of the surface relative to the mandrel axis varies axially along the mandrel. Alternatively, or in addition, the radial extent of the support surface may vary circumferentially, such that relative rotation of the mandrel and expansion member moves the expansion member towards the larger diameter second configuration.  
           [0017]    Preferably, the mandrel defines a plurality of support surfaces, and a corresponding number of expansion members are provided, each defining a respective bearing surface. Most preferably, the support surfaces are positioned circumferentially around the mandrel, and may be tangential to the mandrel. Most preferably the support surfaces are of corresponding circumferential extent and are continuous around the circumference of the mandrel such that, in section, the mandrel has the appearance of a regular polygon.  
           [0018]    Preferably, a plurality of expansion members are provided and in the second configuration collectively define an expansion cone, that is each expansion member defines a cone segment. Most preferably, the cone segments interlock or overlap to define a substantially continuous circumference in the larger diameter second configuration.  
           [0019]    Preferably, the expansion member is adapted to rock or pivot relative to the mandrel as the member moves from the first configuration to the second configuration, that is as the bearing surface moves along the support surface.  
           [0020]    Preferably, at least one end of the expansion member is radially restrained relative to the mandrel, for example a mounting ring may be provided around the mandrel and the end of the member located in the ring. The other end of the expansion member may also be restrained by a further restraining member, to prevent or restrict the member from moving beyond the second configuration.  
           [0021]    Preferably, the tool comprises at least one stop for preventing movement of the expansion member beyond the second configuration. A stop may be provided on the mandrel, for limiting axial movement of the expansion member. The stop may be movable from an initial at least partially retracted position to an extended position, and such movement may be the result of an initial contact between the expansion member and the stop in the at least partially retracted position as the expansion member approaches the second configuration. Alternatively, or in addition, the mandrel and expansion member may define corresponding stop faces. Contact between the faces may be achieved, at least in part, from rocking or pivoting of the expansion member relative to the mandrel.  
           [0022]    Preferably, the expansion member is movable axially relative to the mandrel, and the support surface extends axially of the mandrel. To ensure that the expansion member is moved to the second configuration before the expansion member is advance axially through the tubing to be expanded, means may be provided for initially restraining the expansion member against axial movement relative to the tubing. Such means may take any appropriate form and in a preferred embodiment involves a releasable member, such as a shear fitting, but which may take the form of a simple weld bead on an inner surface of the tubing, which weld bead is intended to be sheared off when the axial force experienced by the bead exceeds the force that it is anticipated will be sufficient to move the expansion member to the second configuration and produce a corresponding initial expansion of the tubing.  
           [0023]    The support surface and bearing surface may initially be spaced apart, such that a significant degree of relative movement between the mandrel and the expansion member is required, or accommodated, before the expansion member begins to move towards the second configuration.  
           [0024]    Preferably, the tool expansion tool includes a seal member adapted to form a fluid seal with surrounding tubing, and which seal member is preferably coupled to the mandrel. The seal member may be in the form of a swab cup. A pressure differential may be created across the seal member, producing a pressure force on the tool, which force may be utilized to move the mandrel relative to the expansion member, or to move the tool through the tubing. This ability to utilize fluid pressure to move the tool through the tubing allows the expansion of the tubing to take place without mechanical intervention from surface. This offers numerous advantages, one being that the tool may be separated from the associated running string during the tubing expansion process, such that, if desired, the running string may be utilized to support the tubing during the expansion process. Thus, it may not be necessary to provide a tubing hanger prior to expansion taking place. Furthermore, the mandrel support surface may itself be utilized as an expansion surface, that is a surface for contact with an inner wall of tubing to be expanded. In one embodiment, the mandrel may be axially translated through a length of tubing to expand the tubing. In a preferred embodiment, the mandrel may be used to provide an initial degree of expansion to a section of profiled tubing, such as described in applicant&#39;s GB0210256.4. The expansion member may be located directly below the section of profiled tubing such that, following expansion of the profiled section, the expansion member is moved to the second configuration and utilized to expand a lower section of tubing, which may be of conventional cylindrical form.  
           [0025]    The presence of the seal member also allows elevated internal fluid pressure to be used to assist in the mechanical tubing expansion process achieved by the contact between the expansion member and the tubing. This assistance may be particularly useful if the reconfiguration of the expansion member takes place in concert with expansion of the tubing. A description of some of the advantages of such an expansion process may be found in applicant&#39;s earlier International Patent Application WO 02/081863, and U.S. patent application Ser. No. 10/102,543, the disclosures of which are incorporated herein by reference.  
           [0026]    Preferably, the tool includes a leading tubing treating or conditioning portion, and most preferably the tubing treating portion is provided in combination with a seal member. Thus, the tubing treating portion may clean the tubing ahead of the seal member, for example removing scale and the like, thus facilitating formation of a seal between the seal member and the tubing, and extending seal life. Preferably, the treating portion is adapted to expand or reform the tubing to a predetermined diameter, to match the seal member, and thus assists in avoiding loss of sealing function where the tubing to be expanded is oval is dented or otherwise has an irregular form. Most preferably, the tubing treating portion is adapted to provide a compliant expansion or reforming function, that is the portion does not define a fixed diameter and is thus capable of negotiating or passing immovable restrictions. Furthermore, the tubing treating portion is preferably spaced from the expansion member when the member is in the second configuration and thus acts to stabilize the expansion member and facilitates straight and consistent expansion; in the absence of such stabilization the expansion member may tend to deviate from the tubing axis as it is translated through the bore, with the result that there is a loss of cylindricality. This feature may also be used to advantage in combination with other forms of expansion member or expansion device, and the stabilization of the expansion member may be of particular assistance in expanding tubing which is differentially stuck in a bore. In such cases, the portion of the tubing wall which is pressed against the bore wall will often experience less extension or deformation than the remainder of the wall, which may result in undesirable thinning or extension of the remainder of the wall. By stabilizing the expansion process by providing the leading conditioning or treating portion this problem may be obviated or mitigated. Without wishing to be bound by theory, it is believed the leading conditioning portion assists in lifting the tubing clear of the bore wall before expansion takes place.  
           [0027]    Other aspects of the invention relate to methods of expanding tubing; and also to various ones of the preferred or alternative features mentioned above which have utility independently of the first aspect. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]    These and other aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0029]    [0029]FIG. 1 is a view of a tubing expansion tool in accordance with an embodiment of the present invention, shown located in tubing to be expanded, and showing the tool in a first configuration;  
         [0030]    [0030]FIG. 2 is a view of the tool of FIG. 1, showing the tool in a second configuration, and showing the tubing following an initial degree of expansion;  
         [0031]    [0031]FIG. 3 is a view of the tool of FIG. 1 and showing the tool in the second configuration and moving through and expanding the tubing; and  
         [0032]    [0032]FIGS. 4, 5,  6 ,  7 ,  8  and  9  are schematic part-sectional views of sequential stages in a tubing expansion operation, utilizing the tubing expansion tool of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0033]    Reference is first made to FIG. 1 of the drawings, which illustrates a tubing expansion tool  10  in accordance with a preferred embodiment of one aspect of the present invention. The tool  10  is shown in a closed first configuration in FIG. 1, while FIGS. 2 and 3 of the drawings show the tool  10  in an open second configuration, and being used to expand a section of downhole tubing  12 . Following a description of the tool  10 , with reference to FIGS. 1, 2 and  3 , the use of the tool  10  in a tubing expansion operation will be described with reference to FIGS.  4  to  9  of the drawings.  
         [0034]    The tool  10  comprises a mandrel  14  having a connector  16  at one end to allow the tool  10  to be releasably mounted at the lower end of a tool string. As will be described, the connector  16  incorporates an internal fishing profile, to allow retrieval of the tool  10  following a tubing expansion operation.  
         [0035]    Mounted to the lower or leading end of the mandrel  14  is a compliant expansion cone  18 . The cone  18  is compliant in the sense that the cone  18  is sized to induce a slight diametric expansion of the tubing  12 , but if the cone  18  should encounter an immovable restriction the slots  20  in the cone  18  permit a degree of radial deflection such that the cone  18  is not stuck fast on encountering such a restriction. The function of the cone  18  is to treat and clean the inner surface of the tubing  12  as the tool  10  advances through tubing  12 , as will be described, and also to ensure that the tubing  12  is of a consistent cylindrical form, that is the cone  18  will tend to remove any ovality or dents in the tubing wall.  
         [0036]    The cone  18  thus conditions the tubing  12  to facilitate operation of a seal member, in the form of a swab cup  22 , which is mounted on the mandrel  14  directly behind the cone  18 . As will be described, a differential pressure across the swab cup  22  urges the tool  10  through the tubing  12  in the direction of arrow A.  
         [0037]    When the tool  10  is in the first or closed position, in which configuration the tool  10  is run into a bore with the tubing  12 , a six segment cone  24  is located on the mandrel  14  towards the leading end of the mandrel  14 , to the rear of the swab cup  22 . The cone  24  comprises six expansion members or segments  26 , the leading ends of which are retained relative to the mandrel  14  by a mounting ring  28 . A hoop spring  30  is located in a series of circumferentially aligned slots  32  formed in the trailing ends of the segments  26  and tends to maintain the cone  24  in the closed position. The trailing ends of the segments  26  are also interlocked with one another by means of co-operating castellations  34  such that, when in the second configuration or open position as illustrated in FIGS. 2 and 3, there are no continuous axial gaps between the segments  26 .  
         [0038]    The inner face of each segment  26  defines a large radius convex arc  36  for co-operating with a respective support surface  38  defined on the outer surface of the mandrel  14 . The support surface  38  defines a concave arc having the same relatively large radius of curvature as the segment bearing surface  36 . As will be described, the configurations of these surfaces  36 ,  38  provide for a large area of support for the segments  26  as they move from the closed position to the open position.  
         [0039]    To open the segments  26 , the mandrel  14  is moved in the direction of arrow A relative to the cone  24 . In use, this movement is induced by a pressure differential acting across the swab cup  22 , a weld bead  40  on the tubing  12  directly in front of the mounting ring  28  ensuring that the cone  24  remains stationary relative to the tubing  12  until the cone  24  has been fully opened.  
         [0040]    As the mandrel  14  moves through the cone  24 , the segments  26  are moved axially along the concave support surfaces  38  and pushed radially outwardly. As the cone  24  in its closed position is only very slightly smaller than the inner diameter of the tubing  12 , the opening of the cone  24  can only be accommodated by diametric expansion of the tubing  12 , as illustrated in FIG. 2. Accordingly, the segments  26  must produce a significant expansion force, and are themselves subject to considerable loads. However, the configuration of the mandrel support surfaces  38  and the segment bearing surfaces  36  are such that the segments  26  are supported over a relatively large proportion of their lengths. The segments  26  thus experience little if any bending as the tubing  12  is expanded. Rather, the loads experienced by the segments  26  are predominantly compression loads, such that significant loads can be experienced by the segments without damage.  
         [0041]    As the cone  24  approaches the trailing end of the mandrel  14 , and the segments  26  approach the fully opened position, the end faces  42  of the segments  26  engage stops  44  which lie within recesses  46  formed in the mandrel. The floor of each recess  46  defines a ramp, such that as a stop  44  is pushed toward the trailing end of the mandrel  14  by the cone segments  26 , the stops  44  ride up the recess floors to a radially extended position, as illustrated in FIG. 2. The stops  44  are T-shaped, such that the base of the stop  44  cannot pass out of the recess  46 , and therefore the stops  44  prevent the segments  26  passing beyond the desired open position.  
         [0042]    A further stop is also provided in the form of lips or ledges on the bearing and support surfaces  36 ,  38 . A ledge  48  is formed on each support surface  38  and a ledge (not shown) is also provided towards the leading end of each bearing surface  36 . As the cone  24  moves along the mandrel  14 , the arcuate form of the surfaces  36 ,  38  is such that the segments  26  tend to pivot or rock such that the bearing surface ledges, which are initially spaced from the corresponding support surfaces, move in towards the support surfaces and as the segments  26  reach the open position the ledges engage, further acting to prevent further, undesired movement of the cone segment  26  relative to the mandrel  14 .  
         [0043]    Once the cone  24  has been opened, application of further axial force to the mandrel  14 , created by the pressure differential across the swab cup  22 , will cause the weld bead  40  to be sheared from the inner surface of the tubing  12 , such that the open cone  18  may be advanced through the tubing  12 , diametrically expanding the tubing  12 , as illustrated in FIG. 3.  
         [0044]    The use of the tool in the deployment of a solid expandable tubular will now be described, with reference to FIGS.  4  to  9  of the drawings, which illustrate such a deployment in accordance with an embodiment of a further aspect of the present invention.  
         [0045]    Reference is first made to FIG. 4, which shows the tool  10  forming the leading end of a tool string  50  mounted on the lower end of a length of drill pipe  52 . The tool string  50  initially supports and is located within the upper end of a section of liner  54  which is to be hung off from existing casing  56 , and subsequently expanded and cemented, as will be described. The tool  10  is located within the liner  54  and straddles a profiled liner section  58 . This liner section  58  has been formed to provide a corrugated or crinkled wall profile. Other than the profiled section  58 , the liner  54  is of a generally cylindrical form and has an outer diameter slightly smaller than the inner diameter of the casing  56 , to provide sufficient clearance for the liner  54  to be run in to the bore through the casing  56 . However, the profiled liner section  58  has previously been shaped into polygonal form, in particular a hexagonal form, in a forming die, and the planar wall portions then further deformed to a concave form such that the outer diameter of the profiled liner section  58  is described by six outer vertices or corners. The minimum inner diameter of the profiled section  58  is defined by the mid-points of the concave wall portions. The unexpanded or closed cone  24  is located below the profiled section  58 , and the mandrel  14  extends upwardly through the profiled section  58  with the radially outwardly extending portions of the support surfaces  38  located adjacent the upper end of the profiled liner section  58 .  
         [0046]    The tool string  50  above the tool  10  includes two fluid actuated rotary expansion tools  60 ,  62 , such as described in applicant&#39;s WO 00/37766 the disclosure of which is incorporated herein by reference, and a running tool  64 .  
         [0047]    In the first stage of the deployment of the liner  54 , the liner  54  is run into the casing  56  and into the open or unlined portion of bore below the casing  56 , to the position as illustrated in FIG. 4. Elevated hydraulic pressure is then communicated through the drill pipe  52  from surface. As the central through-bore which extends through the tool string  50  is closed at the leading end of the expansion tool  10  by a ball  66 , this elevated pressure acts internally of the tool string  50 , which is arranged to unlatch the tool  10  from the remainder of the tool string  50  in response to the elevated pressure.  
         [0048]    The running tool  64  provides a seal against the inner wall of the liner  54  such that the elevated hydraulic pressure which is now communicated to the interior of the upper section of the liner  54  creates a pressure differential across the swab cup  22  at the leading end of the tool  10 . This tends to translate the mandrel  14  downwardly, which initially pulls the mandrel  14  downwards through the profiled liner section  58 . The diameter defined by the mandrel  14 , and in particular the diameter described by the support surfaces  38 , is selected such that the support surfaces  38  contact and urge outwards the inner faces of the concave wall portions of the profiled section  58 . This has the effect of moving the corners of the profiled section  58  radially outwards to describe an increased outer diameter, slightly larger than the internal diameter of the cemented casing  56 . Subsequent translation of the mandrel  14  beyond the profiled section  58  results in expansion or opening of the cone  24 , as was described with reference to FIG. 2 above. This results in expansion of the liner  54  below the profiled section  58  to a larger diameter configuration, to accommodate the expanded cone, and this is illustrated in FIG. 5. This expansion of the liner  54  is of course assisted by the elevated hydraulic pressure, which serves to reduce the mechanical expansion force which must be applied to the wall of the liner  54  by the cone as the cone itself opens or expands.  
         [0049]    The drill pipe  52  is then lifted from surface to lift the liner  54  and pull back the expanded profiled section  58  into the lower end of the casing  56 , as illustrated in FIG. 6. This requires a degree of elastic deformation of the profiled liner section  58 , as the outer diameter described by the expanded section  58  must reduce to allow the section  58  to move into the substantially inelastic casing  56 . This deformation of the profiled liner section  58  is substantially elastic, such that the spring force created in the section  58 , tending to increase the diameter of the section  58 , serves to retain the section  58  securely within the lower end of the casing  56 . The section  58  thus serves as a temporary hanger for the liner  54 .  
         [0050]    Further elevated hydraulic pressure is then communicated through the drill pipe  52  to the interior of the upper section of the liner  54  such that the expanded cone assembly  24  is pumped down through the liner  54 , expanding the liner  54  to a larger diameter, as illustrated in FIG. 7. As the expansion tool  10  is moved through the liner  54 , the leading cone  18  conditions and cleans the inner wall of the liner  54 , removing scale and the like, and taking out any irregularities in the liner form, ahead of the swab cup  22 .  
         [0051]    As noted above, the presence of the elevated fluid pressure surrounding the cone  24  facilitates expansion of the liner  54 , in that expansion is achieved by virtue of a combination of fluid pressure force and mechanical force, advantages of which are described in applicant&#39;s WO 02/081863, the disclosure of which is incorporated herein by reference.  
         [0052]    On reaching a shoe  68  provided at the lower end of the liner  54 , the ball  66  is lifted from its seat within the cone  18 , such that a pressure drop is evident at surface, and the pumps are shut off.  
         [0053]    The expanded liner  54  is now ready to be cemented in the bore. Accordingly, the running tool  64  is unlatched from the upper end of the liner  54  and translated through the expanded liner  54  to once again connect with the upper end of the expansion tool  10 , as illustrated in FIG. 8, such that a “stinger” cementation may be carried out. Typically, this will involve pumping a pre-flush liquid through the drill pipe string  52  and tool string  50 , which liquid will pass out of the lower end of the tool  10 , flow through the liner shoe  68 , pass up through the annulus between the expanded liner  54  and the surrounding open bore wall, pass up between the expanded profiled liner section  58  and the casing  56 , and then pass up between the unexpanded section of liner  54  and the casing  56 . A bottom cement dart is then dropped from surface, followed by a volume of cement and a top dart. Spacer fluid is then pumped into the string above the top dart such that the cement may be passed down through the string and circulated into the annulus, where the cement will set and seal the liner  54  in the bore.  
         [0054]    After completion of the cementing operation the tool string  50  is raised to locate the rotary expansion tools  60 ,  62  within the lower end of the casing  56 . Lifting the string causes the open cone  24  to close down, allowing the tool  10  to be withdrawn through the expanded liner  54 . A ball is then dropped from surface and is caught in the upper end of the tool  10  such that the expansion tools  60 ,  62  may be actuated by pumping hydraulic fluid from surface.  
         [0055]    The actuated expansion tools  60 ,  62  are then rotated and translated over a short distance to roll out expandable high pressure\temperature seals  72  provided on the upper end of the liner  54  and to roll out any unexpanded sections of liner  54 .  
         [0056]    The liner  54  also includes a weak notch profile which, when rolled out, causes the liner to separate, such that once the expansion tool  60 ,  62  are depressurized, the tool string  50  may be pulled back to surface, as shown in FIG. 9.  
         [0057]    It will be apparent to those of skill in the art that the above described embodiment is merely exemplary of the present invention, and that various modifications and improvements may be made thereto, without departing from the scope of the invention. For example, in other embodiments of the invention the liner may be expanded after cement has been circulated into the surrounding annulus. Furthermore, rather than expanding the liner “top-down”, it is possible to expand the liner “bottom-up”. In this regard, the tool  10  offers a number of advantages, primarily that is may be possible to remove the closed tool  10  through a length of unexpanded liner, in contrast to conventional expansion cones. The translation of the cone may be achieved by a combination of pulling on the running string and applied hydraulic pressure behind the cone. Furthermore, in such an operation the liner may be cemented and expanded simultaneously.  
         [0058]    In other embodiments of the invention a number of the features described above may be utilized separately of an expandable cone or expansion device. For example, the liner below the profiled liner section  58  need not necessarily be expanded, and the stinger cementation process may be usefully applied in setting or cementing operations where no expansion of tubing takes place.

Summary:
There are disclosed tools and apparatus for use in expanding downhole tubing.  
     In one embodiment, there is disclosed a tubing expansion tool comprising a mandrel defining at least one curved support surface, and at least one expansion member defining a curved bearing surface for contact with the support surface and corresponding to the mandrel support surface, the member being movable relative to the mandrel whereby the surfaces are in contact and movable over one another to move the expansion member from a smaller diameter first configuration towards a larger diameter second configuration.