Abstract:
A method of expanding tubing comprises locating an expansion tool in a section of tubing to be expanded, applying a fluid pressure to the tubing to create a fluid pressure expansion force and induce a hoop stress in the tubing, and applying a mechanical expansion force to the tubing via the expansion tool. The combined fluid pressure expansion force and mechanical expansion force is selected to be sufficient to induce expansion of the tubing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation of co-pending U.S. patent application Ser. No. 10/114,923, filed Apr. 3, 2002, which claims benefit of Great Britain application 0108638.8, file Apr. 6, 2001. Each of the related aforementioned patent applications are hereby incorporated by reference in their entireties. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to tubing expansion, and in particular to expansion of tubing downhole.  
           [0004]    2. Description of the Related Art  
           [0005]    The oil and gas exploration and production industry is making increasing use of expandable tubing, primarily for use as casing and liner, and also in straddles, and as a support for expandable sand screens. Various forms of expansion tools have been utilised, including expansion dies, cones and mandrels which are pushed or pulled through tubing by mechanical or hydraulic forces. However, these tools require application of significant force to achieve expansion and must be packed with grease to serve as a lubricant between the faces of the cone and the tubing. A number of the difficulties associated with expansion cones and mandrels may be avoided by use of rotary expansion tools, which feature rolling elements for rolling contact with the tubing to be expanded while the tool is rotated and advanced through the tubing; a range of such tools is disclosed in WO00\37766, the disclosure of which is incorporated herein by reference. Although the expansion mechanism utilised in rotary expansion tools tends to require only relatively low actuation forces, the various parts of the tools may experience high loading, for example the rollers may experience very high point loads where the roller surfaces contact the tubing under expansion. Clearly, such high loadings increase the rate of wear experienced by the tools and the requirement to build the tools with the ability to withstand such loads tends to increase the cost and complexity of the tools.  
           [0006]    GB 2348223 A, GB 2347950 A and GB 2344606 A (Shell Internationale Research Maatschappij B.V.) disclose various arrangements in which a tubular member is extruded off a mandrel to expand the member. The axial force necessary to extrude and thus expand the member is achieved by creating an elevated fluid pressure chamber in the tubular member below the mandrel, which pressure creates an axial force on the closed end of the tubular member below the mandrel sufficient to pull the member over the mandrel. The elevated fluid pressure acts only the expanded portion of the tubular member below the mandrel.  
           [0007]    U.S. Pat. No. 5,083,608 (Abdrakkhmanov et al) discloses an arrangement for patching off troublesome zones in a well. The arrangement includes profile pipes which are run into a borehole and then subject to elevated internal pressure to straighten the pipes and bring them into engagement with the surrounding wall of the borehole. A reamer is then rotated within the straightened pipes, with an axial load being applied to the reamer. The reamer is utilised to expand the threaded joints of the pipe and to further straighten the pipe, and also to provide clearance between a seal on the reamer and the inner wall of the pipe which was utilised to permit the original fluid pressure induced straightening of the pipe.  
           [0008]    It is among the objectives of the present invention to provide an expansion method and apparatus which obviates or mitigates one or more disadvantages of the prior art expansion arrangements.  
         SUMMARY OF THE INVENTION  
         [0009]    According to the present invention there is provided a method of plastically expanding a tubing, the method comprising:  
           [0010]    Applying a fluid pressure expansion force to a section of tubing; and  
           [0011]    Locating an expansion tool in the pressurised tubing and applying a mechanical expansion force to the pressurised tubing section, the combined fluid pressure force and mechanical expansion force being selected to be sufficient to induce yield of the tubing.  
           [0012]    The invention also relates to apparatus for providing such expansion.  
           [0013]    The use of a combination of fluid pressure and mechanical forces allows expansion to be achieved using a lower fluid pressure than would be necessary to achieve expansion when relying solely on fluid pressure to induce expansion, and furthermore provides far greater control of the expansion process; it is generally difficult to predict the form of the expanded tubing that will result from a solely fluid pressure-induced expansion, and failure of tubing in such circumstances is common. Also, the combination of fluid pressure and mechanically-induced expansion allows expansion to be achieved while the loads experienced by the mechanical expansion tool remain relatively low, greatly extending he life of the tools. By way of example, a tubing may be subject to an internal fluid pressure selected to induce a hoop tensile stress which represents 60% of yield. By then applying an additional mechanically-applied expansion force sufficient to induce yield, the tubing may be expanded. Of course the relative proportions of the stress contributed by the fluid pressure and by the expander tool may be varied to suit particular applications, and issues to be taken into account may include: the nature of the tubing to be expanded, as lower quality tubing may respond in an unpredictable manner to elevated hydraulic pressures, such that a greater proportion of the stress may be mechanically applied, and thus greater control exercised over the expansion process; and the capabilities of the apparatus available, for example pump or fluid conduit capabilities may place limits on the applied fluid pressures.  
           [0014]    Various prior art proposals have utilised expansion dies or cones which are urged through tubing under the influence of an axial fluid pressure force acting on the die or cone, or in which tubing is extruded from a mandrel under the influence of axial fluid pressure force acting on the expanded tubing below the mandrel. However, in these instances the fluid pressure force is applied behind or below the die or cone, and the section of the tubing under expansion is not exposed to the elevated die-driving or tubing-extruding fluid pressure. Indeed, in order to provide the force necessary to drive the die or mandrel forward relative to the tubing in such existing arrangements, and to prevent leakage of the driving fluid past the die, it is necessary that there is an effective pressure-tight seal between the die and the expanded tubing. This seal may be provided by the contact between the die and the tubing wall, or by a separate seal assembly provided on the die.  
           [0015]    It is a further advantage of the present invention that the fluid being utilized to pressurise the tubing may also serve as a lubricant between the expansion tool and the tubing, facilitating relative movement therebetween and thus reducing the degree of force necessary to move the expansion tool through the tubing. This is of particular significance where the expansion tool is a die or cone, and the pressurizing fluid provides an effectively infinite supply of lubricant, as opposed to the finite supply of grease or other lubricant provided in conventional expansion arrangements, (see, for example, GB 2344606 A, in which a body of lubricant  275  is provided in the unexpanded portion of the tubing above the expansion mandrel); once the lubricant has been exhausted, the cone must be retrieved to the surface and repacked. Of course the presence of a lubricant will also reduce the rate of wear to the bearing portions of the expansion tool.  
           [0016]    Although intended primarily for use in expanding bore lining metal tubing, the invention has application in other downhole applications, and may also be used in subsea or surface applications.  
           [0017]    The expansion tool may take any appropriate form, including an expansion die or cone, and may be in the form of a cone or other member carrying a plurality of rollers rotatable about axes substantially perpendicular to the tubing axis. However, it is preferred that the expansion tool is a rotary expansion tool, or rolling element expander, that is the tool features at least one expansion member which, in use, is in rolling contact with the tubing wall; the expansion member may follow a circumferential or helical contact path with the tubing wall. Most preferably, the expansion members are conical in form or are mounted on axes arranged to define a cone. In another embodiment of the invention, a rotating expansion tool may be utilised which features a non-rotating expansion member or members, preferably of a relatively hard material such as a ceramic material, which provides a sliding contact with the tubing wall. The members may be radially extendable or may be radially fixed. In one embodiment, blocks of silicon carbide or titanium carbide may form the expansion members.  
           [0018]    Preferably, the expansion tool is fluid pressure actuated, and may include a hydraulic drive motor to rotate the tool; the motor may utilise the fluid providing the expansion force as a drive fluid, the fluid exhausting into a lower pressure section of the bore isolated from the expansion section. In other embodiments, an electric motor may be utilised.  
           [0019]    The expansion tool is preferably provided in combination with a seal assembly, for providing a fluid-tight seal with the unexpanded tubing ahead of the expansion tool. As the fluid pressure in the unexpanded tubing ahead of the seal assembly will tend to be lower than the elevated pressure behind the seal assembly, this differential pressure will tend to produce an axial pressure force acting on the seal assembly, which may be utilised to drive the expansion tool forwards. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    These and other aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0021]    [0021]FIG. 1 is a schematic sectional view of tubing expansion apparatus in accordance with a preferred embodiment of the present invention,  
         [0022]    [0022]FIG. 2 is a diagrammatic part-sectional view of an expansion tool of expansion apparatus in accordance with another embodiment of the present invention;  
         [0023]    [0023]FIGS. 3, 4,  5  and  6  are sectional views on lines  3 - 3 ,  4 - 4 ,  5 - 5  and  6 - 6  of FIG. 2; and  
         [0024]    [0024]FIG. 7 is a diagrammatic part-sectional view of an expansion apparatus in accordance with a further embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]    Reference is first made to FIG. 1 of the drawings, which illustrates expansion apparatus  10  in accordance with a preferred embodiment of the present invention, shown located in the upper end of a section of tubing in the form of bore liner of expandable metal, hereinafter referred to as liner  12 . In use, the apparatus  10  and liner  12  are run into a drilled bore together, and the liner  12  positioned in a section of unlined bore, and possibly overlapping the lower end of existing bore-lining casing. The apparatus  10  is then operated to expand the liner  12  to a larger diameter, the liner of the original, unexpanded diameter being identified as liner  12   a , and the expanded larger diameter liner being identified by the reference numeral  12   b.    
         [0026]    The apparatus  10  includes a rolling element expander  14  having a generally conical body  16  carrying a number of rolling elements  18 . The expander  14  is coupled to a hydraulic drive motor  20  mounted on a running tube  22  which extends upwardly, through a stuffing box  24 , to surface. The stuffing box  24  is provided in an upper seal assembly  26  mounted to the top of the liner  12 . Mounted below the expander  14 , via a swivel  28 , is a lower seal assembly  30  which is adapted to provide a sliding seal with the unexpanded liner  12   a.    
         [0027]    In use, the volume  32  defined by the liner  12  between the seal assemblies  26 ,  30  is supplied with high pressure hydraulic fluid from an appropriate source, such as a surface or downhole pump. In FIG. 1 a hydraulic fluid inlet  34  is illustrated as passing radially through a part of the upper seal assembly  26 , however in practice the inlet  34  would be arranged axially, to allow accommodation of the apparatus  10  in a bore, and to allow supply of hydraulic fluid via a running tube in the form of a coaxial coil tubing or drill pipe. The pressure of the hydraulic fluid is selected to induce a predetermined hoop tensile stress within the liner  12 . The hydraulic fluid exhausts through the drive motor  20 , which includes a hydraulic fluid driven turbine, the exhausted fluid passing up to the surface via the running tube  22 .  
         [0028]    The exhausted fluid is throttled, or the flow and pressure of the fluid otherwise controlled, to control the pressure within the volume  32 , and also the operation of the motor. The throttling may take place downhole or at surface.  
         [0029]    The passage of fluid through the motor  20  causes the motor to rotate the expander  14 , and thus if the motor  20  is advanced through the liner  12 , the expander  14  will act on the transition portion  12   c  between the section of unexpanded and expanded liner  12   a ,  12   b . The forces acting on the transition portion  12   c  comprise a combination of the stress induced by the elevated hydraulic fluid pressure within the volume  32 , and the mechanical pressure forces applied by the surfaces of the rolling elements  18 . The combination of forces is selected so as to be sufficient to induce yield and thus plastic deformation of the liner  12 .  
         [0030]    As noted above, the lower seal assembly  30  isolates the pressurised volume  32  from the remainder of the unexpanded liner  12   a , which is at a lower pressure than the volume  32 . Accordingly, the differential pressure acting on the assembly  30  produces an axial force tending to push the apparatus  10  through the liner  12 . There is thus no requirement to apply weight from surface to the apparatus  10 .  
       EXAMPLE  
       [0031]    A liner  12  to be expanded is 7⅝″ 29.7 lb\ft N80 tubing which has a burst pressure of approximately 7,000 psi. The hydraulic fluid supplied to the volume  32  is at 5,000 psi. The liner wall is therefore subjected to a tensile stress of 51,000 psi, which represents 63% of the yield for the liner (not taking into account the effect of radial stress in the region of 25,000 psi).  
         [0032]    The drive fluid to the hydraulic motor  20  enters through an inlet port  36  and exhausts into the running tube  22 , thereby adding the motor pressure drop to the applied internal pressure. The hydraulic return to surface is throttled to maintain the applied liner pressure, taking into account the motor pressure drop and the parasitic losses in the running tube  22 .  
         [0033]    The net axial force applied to the expansion assembly is the pressure differential across the lower seal assembly  30  times its cross-sectional area minus the pressure differential across the stuffing box  24  times the cross-sectional area of the running tube  22 . If the running tube  22  has an outside diameter of 5″ and the internal diameter of the 7⅝″ liner is 6.88″ , then the down force applied to the assembly is 83,000 lbf, which is in excess of the force required to drive the expander  14  through the liner  12 , such that a braking assembly must be provided on surface for the running tube  22 . Alternatively, a larger diameter running tube  22  could be utilised.  
         [0034]    Reference is now made to FIGS.  2  to  6  of the drawings, which illustrate an alternative expander  40  in accordance with a further embodiment of the present invention, shown located in a section of liner  42  during expansion. From a comparison of the figures, those of skill in the art will recognise that FIG. 2 shows various internal features of the expander  40 .  
         [0035]    The expander  40  features a generally conical body  44  on which are mounted five rows of rollers  46 ,  47 ,  48 ,  49  and  50  (the section shown in FIG. 6 corresponds to both sections  6 - 6  and  6   a - 6   a  of FIG. 2). Unlike the rolling elements  18  of the first described embodiment, the rollers  46  to  50  rotate around axes that lie substantially perpendicular to the liner axis, and the expander  40  is therefore intended to advance axially through the liner  42 , without rotation.  
         [0036]    Such an expander configuration would not be practical in the absence of assisting hydraulic expansion forces, as the bearing loads experienced on expanding heavy walled tubing would far exceed the capabilities of the bearings that could be installed in the limited space available. However, with applied internal hydraulic pressure providing the bulk of the expansion forces, the roller bearings are relatively lightly loaded.  
         [0037]    Reference is now made to FIG. 7 of the drawings, which illustrates an expansion apparatus  60  in accordance with a further embodiment of the present invention located within a partially expanded borehole liner  58 .  
         [0038]    The apparatus  60  includes an expander cone  62  mounted to a tubular running string  64 , and mounted below the cone  62  is a seal assembly  66  adapted to provide a sliding seal with the unexpanded liner  58 .  
         [0039]    As with the above described embodiments, an elevated fluid pressure above the seal assembly  66  provides an initial expansion force acting on the liner  58 , while the passage of the cone  62  provides a further mechanical expansion force which, in combination with the hydraulic expansion force, is sufficient to induce yield in the liner  58 . The axial pressure force acting on the seal assembly  66  may also serve to drive the cone  60  through the tubing  58 , and the presence of the pressurising force around the cone  62  provides an effectively infinite supply of lubricant for the cone  62 ; fluid communication across the cone  62  may be assured by provided linked ports  68 ,  70  above and below the cone  62 .  
         [0040]    It will be apparent to those of skill in the art that the above-described embodiments provide an alternative method for expanding tubing downhole, and that the invention offers a number of advantages over existing systems.  
         [0041]    Furthermore, those of skilled in the art will recognise that the above-described embodiments are merely exemplary of the present invention, and that various modifications and improvements may be made thereto, without departing form the scope of the invention. For example, in the embodiment of FIG. 1, rather than providing a hydraulic fluid driven motor  20  within the pressurised volume  32 , a motor may be provided externally of the volume  32 , and may be located downhole or at surface. In this case, the upper seal assembly  26  would of course have to be modified to accommodate rotation.