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: 
FIELD OF THE INVENTION 
     The present invention relates to an expander for radially expanding a tubular element. 
     BACKGROUND OF THE INVENTION 
     In the industry of hydrocarbon oil and gas production it has been proposed to radially expand a tubular element extending in a wellbore formed into an earth formation. The tubular element can be, for example, a wellbore casing which is, after expansion thereof, cemented in the wellbore. In conventional wellbore drilling the wellbore is drilled and cased in sections whereby after drilling and casing each section, the wellbore is drilled deeper and a next casing section is lowered through the previous casing section. Thus, the next casing section necessarily has to be of smaller outer diameter than the inner diameter of the previous casing section. By radially expanding each casing section after installation thereof in the wellbore, it is achieved that the lower wellbore part still is of a sufficiently large diameter. 
     It has been proposed to expand each casing section by pulling, pushing or pumping a rigid expander through the casing section whereby the expander has an outer diameter larger than the inner diameter of the unexpanded casing. By virtue of the phenomenon that the inner diameter of the casing after expansion is slightly larger than the outer diameter of the expander (generally referred to as “surplus expansion”), the expander can be moved through expanded casing portions with some clearance. However, a problem of the known expander is that it is impossible to move the expander through unexpanded portions of the casing. 
     It has further been proposed to apply a collapsible expander which can be moved through the casing when in the collapsed position. One such collapsible expander is disclosed in U.S. Pat. No. 6,012,523, which expander is provided with hingeable segments (also termed fingers) which axially slide over a conically shaped body portion to form the final expanded cone. A drawback of this expander is that the hinges of the segments are subjected to high (friction) loads during the expansion process. Another drawback of the expander is that small clearances between the segments cause extrusion of the tubular element into such clearances thereby causing axial tracks on the inside of the expanded tube, which tracks form insufficiently expanded portions at the inner surface of the tubular element. 
     Accordingly there is a need for an improved expander which overcomes the aforementioned drawbacks. 
     SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the invention there is provided an expander for radially expanding a tubular element, comprising
     an expander body connectable to an elongate member for moving the expander in axial direction through the tubular element, the expander body having a first body portion and a second body portion axially displaced from the first body portion, wherein the first body portion has a larger outer diameter than the second body portion;   a set of expander segments arranged around the expander body, each segment being movable relative the expander body between a radially extended position in which the segment is axially aligned with the first body portion and a radially retracted position in which the segment is axially aligned with the second body portion; and   actuating means for moving each segment between the extended position and the retracted position;
 
wherein the segment and the first body portion are provided with co-operating support profiles for preventing axial movement of the segment relative to the first body portion during expansion of the tubular element whereby the segment is in the extended position.
   

     It is thereby achieved that the co-operating support profiles transfer the axial friction forces acting on each segment to the expander body, so that the actuating means (e.g. a hinge or a leaf spring) of the segment is relieved from transfer of the high friction forces. 
     In another aspect of the invention there is provided an expander for radially expanding a tubular element, comprising
     an expander body connectable to an elongate member for moving the expander in axial direction through the tubular element, the expander body having a first body portion and a second body portion axially displaced from the first body portion, wherein the first body portion has a larger outer diameter than the second body portion;   a set of expander segments arranged around the expander body, each segment being movable relative the expander body between a radially extended position in which the segment is axially aligned with the first body portion and a radially-retracted position in which the segment is axially aligned with the second body portion; and   actuating means for moving each segment between the extended position and the retracted position thereof;
 
wherein the expander segments when in their respective radially extended positions, form a substantially continuous cone surface, and wherein each pair of adjacent segments have a common boundary line along the cone surface, said boundary line extending inclined relative to the longitudinal axis of the expander.
   

     By the arrangement that the common boundary line, which represents a small clearance between adjacent segments, extends inclined relative the longitudinal axis, it is achieved that the expander moves against the full inner surface of the tubular element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       The invention will be described hereinafter in more detail and by way of example with reference to the accompanying drawings in which: 
         FIG. 1  schematically shows a side view, partly in longitudinal section, of first embodiment of an expander of the invention, when in a radially unexpanded mode; 
         FIG. 2A  schematically shows a side view, partly in longitudinal section, of the expander of  FIG. 1 , when in a radially expanded mode; 
         FIG. 2B  schematically shows a side view of the expander of  FIG. 1 , when in a radially expanded mode; 
         FIG. 3  schematically shows a side view of a second embodiment of an expander of the invention, when in a radially unexpanded mode; 
         FIG. 4  schematically shows a side view of the expander of  FIG. 3 , when partially radially expanded; and 
         FIG. 5  schematically shows a side view of the expander of  FIG. 3 , when fully radially expanded. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1  there is shown a first embodiment of an expander  1  for radially expanding a tubular element (not shown) such as a casing extending in a wellbore. The expander  1  includes an elongate expander body  2  connected to a pulling string  4  for pulling the expander  1  through the casing. The expander body  2  has two small diameter portions  6 ,  8  and a large diameter portion  10  arranged inbetween the small diameter portions  6 ,  8 . The large diameter portion  10  is provided with an annular support edge  12  defining an annular support surface  14  (i.e. an annular shoulder) extending substantially in radial direction, which support edge  12  is located about centrally of the axial length of the large diameter portion  10 . Furthermore, the large diameter body portion  10  has a first frustoconical surface  16  tapering down from the support edge  12  to the small diameter portion  6 , and a second frustoconical surface  18  tapering down from the support edge  12  to the small diameter portion  8 . 
     The expander  1  further comprises a plurality of expander segments of which a set of primary segments  24  is arranged around the small diameter portion  6  of body  2 , and of which a set of secondary segments  26  is arranged around the small diameter portion  8  of body  2 . Each primary segment  24  is connected by a respective hinge  28  to a primary actuating sleeve  30  surrounding the small diameter portion  6 , and each secondary segment  26  is connected by a respective hinge  32  to a secondary actuating sleeve  34  surrounding the small diameter portion  8 . The respective assemblies of primary actuating sleeve  30  and primary segments  24 , and secondary actuating sleeve  34  and secondary segments  26 , are axially movable relative to the expander body  2  whereby during movement of the primary segments  24  along the first frustoconical surface  16  the segments  24  hinge relative to the primary actuating sleeve  30 , and whereby during movement of the secondary segments  26  along the second frustoconical surface  18  the segments  26  hinge relative to the secondary actuating sleeve  34 . Each primary segment  24  has at its inner surface a support profile  38  which is complementary in shape to the support edge  12  so that, when the assembly of primary actuating sleeve  30  and primary segments  24  is fully moved against the large diameter body portion  10 , said support profile  38  is biased against the annular surface  14  of support edge  12 . 
     Reference is further made to  FIG. 2A , showing the expander  1  whereby both the primary segments  24  and the secondary segments  26  have been fully moved against the large diameter body portion  10 . In this position the primary segments  24  and secondary segments  26  are hinged radially outward and rest against the respective first and second frustoconical surfaces  16 ,  18 , whereby the support profile  38  of each primary segments  24  is biased against the annular surface  14  of support edge  12 . Furthermore, in  FIG. 2  is shown a primary locking sleeve  40  axially movable relative to the primary segments  24  between an unlocking position in which the locking sleeve  40  is arranged remote from the segments  24  and a locking position in which the sleeve  40  closely surrounds the segments  24 , and a secondary locking sleeve  42  axially movable relative to the secondary segments  26  between an unlocking position in which the locking sleeve  42  is arranged remote from the segments  26  and a locking position in which the sleeve  42  closely surrounds the segments  26 . 
     In  FIG. 2B  is shown a side view of the expander  1  with the segments  24 ,  26  in the radially expanded position. As shown, the primary segments  24  and the secondary segments  26  have respective axially overlapping portions  44 ,  46  which are staggeredly arranged when seen in circumferential direction. 
     In  FIG. 3  is shown a second embodiment of an expander  51  for radially expanding a tubular element (not shown) such as a casing extending in a wellbore. The expander  51  includes an elongate expander body  52  connected to a pulling string  54  for pulling the expander  50  through the casing. The expander body  52  has a small diameter portion  56  and a large diameter portion  60  arranged at one end of the small diameter body portion  56 . The large diameter portion  60  is provided with two annular support edges  62 ,  64  defining respective annular support surface  65 ,  66 , each extending substantially in radial direction. The large diameter body portion  60  has a frustoconical surface  68  tapering down from the support edge  62  to the small diameter portion  56 . 
     The expander  51  is provided with a plurality of expander segments including a set of primary segments  70  and a set of secondary segments  72 , both sets being arranged around the small diameter body portion  56  whereby the secondary segments  72  are arranged axially remote from the large diameter body portion  60  and the primary segments  70  are arranged between the set of secondary segments  72  and the large diameter body portion  60 . The primary segments  70  and secondary segments  72  are staggeredly arranged when seen in circumferential direction. Furthermore, the width of each primary segment  70  increases in axial direction away from the pulling string  54 , and the width of each secondary segment is substantially constant in axial direction. 
     Each primary segment  70  is connected by a respective hinge  74  (or a leaf spring) to a primary actuating sleeve  76 , and each secondary segment  72  is connected by a respective hinge or leaf spring (not shown) to a secondary actuating sleeve  80 . The actuating sleeves  76 ,  80  are arranged concentrically around the small diameter body portion  56  whereby primary actuating sleeve  76  extends around secondary actuating sleeve  80 . The secondary actuating sleeve  80  is provided with a top ring  81 . 
     The respective assemblies of primary actuating sleeve  76  and primary segments  70 , and secondary actuating sleeve  80  and secondary segments  72 , are axially movable relative to each other and relative to the expander body  52 . During movement of the segments  70 ,  72  along the frustoconical surface  68  the primary segments  70  hinge relative to the primary actuating sleeve  76  and the secondary segments  72  hinge relative to the secondary actuating sleeve  80 . Each segment  70 ,  72  has at its inner surface a support profile  84  which is complementary in shape to the support edges  62 ,  64  so that, when the primary segments  70  and secondary segments  72  are fully moved against the large diameter body portion  60 , the support profile  84  of each segment is in abutment with the annular support surfaces  65 ,  66 . 
     A locking sleeve  86  arranged around the set of secondary segments  72 , is axially movable between an unlocking position in which the locking sleeve  86  is axially displaced from the primary segments  70  when these are axially displaced from the large diameter body portion  60 , and a locking position in which the locking sleeve  86  closely surrounds the segments  70 ,  72  when these are biased against the large diameter body portion  60 . 
     In  FIG. 4  is shown the expander  51  whereby the respective assemblies of primary actuating sleeve  76  and primary segments  70 , and secondary actuating sleeve  80  and secondary segments  72 , have been moved towards the large diameter body portion  60  whereby the primary segments  70  are biased against the large diameter body portion  60 . 
     In  FIG. 5  is shown the expander  51  whereby the respective assemblies of primary actuating sleeve  76  and primary segments  70 , and secondary actuating sleeve  80  and secondary segments  72 , have been further moved towards the large diameter body portion  60  whereby both sets of primary segments  70  and secondary segments  72  are biased against the large diameter body portion  60 . As illustrated in  FIG. 5 , the expander segments  70 ,  72  when biased against the large diameter body portion  60 , form a substantially continuous cone surface whereby for each pair of adjacent segments  70 ,  72  there is defined a common boundary line  90  (representing a small clearance between the adjacent segments) along the cone surface, which boundary line extends inclined relative to the longitudinal axis of the expander  51 . 
     During normal operation of the first embodiment, the expander  1  is lowered into the wellbore casing to be expanded at pulling string  4 , whereby the expander  1  is in the unexpanded mode shown in  FIG. 1 . When the expander has reached the lower end of the casing, the actuating sleeves  30 ,  34  are axially moved towards the large diameter body portion  10  by a suitable actuating device (not shown). By virtue of the movement of sleeve  30 , the primary segments  24  move along the first frustoconical surface  16  until the support profile  38  become biased against the annular support surface  14 . By virtue of the movement of the sleeve  34 , the secondary segments  24  move along the second frustoconical surface  18  until the secondary segments  24  abut against the second frustoconical surface  18 . It has thus been achieved that the primary and secondary segments have hinged radially outwardly, as shown in  FIGS. 2A and 2B . The locking sleeves  40 ,  42  are then moved to their respective locking positions (as shown in  FIGS. 2A ,  2 B). 
     The expander  1  is then pulled through the casing by means of pulling string  4  so as to radially expand the casing in the wellbore. During the expansion process, the segments  24 ,  26  are subjected to friction forces from the inner surface of the casing, whereby especially the primary segments  24  are subjected to high friction forces. For each primary segment, the friction forces are transmitted via the support profile  38  to the annular support surface  14  of the large diameter body portion  10 . It is thereby achieved that the hinges  28  (or leaf springs) are not subjected to the high friction forces, and the risk of damage to the hinges  28  has thereby been considerably reduced. Furthermore, it is achieved that the locking sleeves  40 ,  42  keep the respective sets of primary secondary segments closely biased against the large diameter body portion  10  and thereby assist in reducing transfer of friction forces to the hinges  28 ,  32  or leaf springs. 
     When the casing has been fully expanded, the expander  1  is removed from the casing and brought back to its unexpanded mode (as shown in  FIG. 1 ) for future use. 
     During normal operation of the second embodiment, the expander  51  is lowered into the casing to be expanded at pulling string  54 , whereby the expander  51  is in the unexpanded mode shown in  FIG. 3 . When the expander has reached the lower end of the casing, the actuating sleeves  76 ,  80  are simultaneously moved towards the large diameter body portion  60  by means of a suitable device (not shown) actuating the top ring  81 . By virtue of the movement of primary actuating sleeve  76 , each primary segment  70  moves along the frustoconical surface  68  until its support profile  84  becomes biased against the annular support surfaces  65 ,  66  (as shown in  FIG. 4 ). From this position on, the primary actuating sleeve  76  is held stationary and the secondary actuating sleeve  80  is moved further towards large diameter portion  60  so that each secondary segment  72  moves along the frustoconical surface  68  until its support profile  84  becomes biased against the annular support surfaces  65 ,  66 . It has thus been achieved that the primary and secondary segments  70 ,  72  have hinged radially outwardly so as to form the substantially continuous cone surface referred to hereinbefore. In a next step the locking sleeve  86  is axially moved against the segments  70 ,  72  so as to retain the segments closely against the large diameter body portion  60 . 
     The expander  51  is then pulled through the casing by means of pulling string  54  so as to radially expand the casing in the wellbore. During the expansion process, the segments  70 ,  72  are subjected to friction forces from the inner surface of the casing, which forces act in the direction away from the pulling string  4 . For each segment, the friction forces are transmitted via the support profile  84  to the annular support surfaces  65 ,  66  of the large diameter body portion  60 . It is thereby achieved that the hinges (or leaf springs) of the segments  70 ,  72  are not subjected to the (high) friction forces, and the risk of damage to the hinges has thereby been considerably reduced. Furthermore, it is achieved that the locking sleeve  86  keeps the respective sets of primary secondary segments  70 ,  72  closely biased against the large diameter body portion  60  and thereby assist in reducing transfer of friction forces to the hinges. Another advantage of the second embodiment is that the cone surface formed by the combined segments  70 ,  72  moves along the entire inner surface of the casing by virtue of the feature that the small clearance between adjacent (represented by line  90  in  FIG. 5 ) extends inclined relative to the longitudinal axis of the expander  51 . 
     When the casing has been fully expanded, the expander  1  is removed from the casing and brought back to its unexpanded mode (as shown in  FIG. 3 ) for future use. 
     Instead of pulling the expander through the casing, the expander can pumped or pushed through the casing. 
     In a modification of the first embodiment, each secondary segment has at its inner surface a support profile which co-operates with a support edge provided at the expander body in the same manner as the support profile/support edge system described with respect to each primary segment. 
     While the illustrative embodiments of the invention have been described with particularity, it will be understood that various other modifications will be readily apparent to, and can be easily made by one skilled in the art without departing from the spirit of the invention. Accordingly, it is not intended that the scope of the following claims be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all features which would be treated as equivalents thereof by those skilled in the art to which this invention pertains.

Summary:
An expander for radially expanding a tubular element, comprising an expander body connectable to an elongate member for moving the expander in axial direction through the tubular element, the expander body having a first body portion and a second body portion axially displaced from the first body portion, wherein the first body portion has a larger outer diameter than the second body portion. A set of expander segments is arranged around the expander body, each segment being movable relative the expander body between a radically extended position in which the segment is axially aligned with the first body portion and a radially retracted position in which the segment is axially aligned with the second body portion. Actuating means is provided for moving each segment between the extended position and the retracted position. Each segment and the first body portion are provided with co-operating support profiles for preventing axial movement of the segment relative to the first body portion during expansion of the tubular element whereby the segment is in the extended position.