Abstract:
Apparatus and methods are disclosed for anchoring a first conduit to a second conduit. The first conduit is typically an expandable conduit whereby at portion of the first conduit is expanded by applying a radial force thereto to provide an anchor and/or seal between the first and second conduits. An inflatable device is provided that can be used to provide a temporary anchor while the first (expandable) conduit is radially expanded. An expander device that is capable of applying a radial expansion force to the first conduit is optionally attached to the inflatable device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is the U.S. national phase application of PCT International Application No. PCT/GB00/03406, filed. Sep. 6, 2000. 

   FIELD OF THE INVENTION 
   The present invention relates to an apparatus for and a method of anchoring a first conduit to a second conduit, the apparatus and method particularly, but not exclusively, using an inflatable device to provide a temporary anchor. 
   BACKGROUND OF THE INVENTION 
   A borehole is conventionally drilled during the recovery of hydrocarbons from a well, the borehole typically being lined with a casing. Casings are installed to prevent the formation around the borehole from collapsing. In addition, casings prevent unwanted fluids from the surrounding formation from flowing into the borehole, and similarly, prevents fluids from within the borehole escaping into the surrounding formation. 
   Boreholes are conventionally drilled and cased in a cascaded manner; that is, casing of the borehole begins at the top of the well with a relatively large outer diameter casing. Subsequent casing of a smaller diameter is passed through the inner diameter of the casing above, and thus the outer diameter of the subsequent casing is limited by the inner diameter of the preceding casing. Thus, the casings are cascaded with the diameters of the casing lengths reducing as the depth of the well increases. This gradual reduction in diameter results in a relatively small inside diameter casing near the bottom of the well that could limit the amount of hydrocarbons that can be recovered. In addition, the relatively large diameter borehole at the top of the well involves increased costs due to the large drill bits required, heavy, equipment for handling the larger casing, and increased volumes of drill fluid that are required. 
   Each casing is typically cemented into place by filling cement into an annulus created between the casing and the surrounding formation. A thin slurry cement is pumped down into the casing followed by a rubber plug on top of the cement. Thereafter, drilling fluid is pumped down the casing above the cement that is pushed out of the bottom of the casing and into the annulus. Pumping of drilling fluid is stopped when the plug reaches the bottom of the casing and the wellbore must be left, typically for several hours, whilst the cement dries. This operation requires an increase in rig time due to the cement pumping and hardening process, that can substantially increase production costs. 
   It is known to use a pliable casing that can be radially expanded so that an outer surface of the casing contacts the formation around the borehole. The pliable casing undergoes plastic deformation when expanded, typically by passing an expander device, such as a ceramic or steel cone or the like, through the casing. The expander device is propelled along the casing in a similar manner to a pipeline pig and may be pushed (using fluid pressure for example) or pulled (using drill pipe, rods, coiled tubing, a wireline or the like). 
   Lengths of expandable casing are coupled together (typically by threaded couplings) to produce a casing string. The casing string is inserted into the borehole in an unexpanded state and is subsequently expanded using the expander device, typically using a substantial force to facilitate the expansion process. However, the unexpanded casing string requires to be anchored either at or near an upper end or a lower end thereof during the expansion process to prevent undue movement. This is because when the casing string is in an unexpanded state, an outer surface of the casing string does not contact the surrounding borehole formation or an inner face of a pre-installed casing or liner (until at least a portion of the casing has been radially expanded), and thus there is no inherent initial anchoring point. 
   Slips are conventionally used to temporarily anchor the unexpanded casing to the borehole during the expansion process. Slips are generally wedge-shaped, steel, hinged portion that provide a temporary anchor when used. Slips are actuated whereby the wedge-shaped portions engage with the surrounding borehole formation or a casing or liner. 
   However, the mechanical configuration of slips often causes damage to the casing or liner. In some cases, the damage causes the slip to fail due to a loss of mechanical grip. Slip-type devices in open-hole engaging formation are often prone to slippage also. 
   SUMMARY OF THE INVENTION 
   According to a first aspect of the present invention, there is provided an apparatus for anchoring a first conduit to a second conduit, the apparatus comprising an inflatable device for engaging with the first conduit, wherein the inflatable device is inflatable to facilitate anchoring of the first conduit to the second conduit. 
   According to a second aspect of the present invention, there is provided a method of anchoring a first conduit to a second conduit, the method comprising the steps of providing a first conduit, providing an inflatable device in contact with the first conduit, running the first-conduit and inflatable device into the second conduit, and subsequently inflating the inflatable device to facilitate anchoring of the first conduit to the second conduit. 
   According to a third aspect of the present invention, there is provided a method of anchoring an expandable conduit to a second conduit, the method comprising the steps of providing an expandable conduit, running the first conduit into the second conduit, passing an inflatable device into the conduit, and subsequently inflating the inflatable device to facilitate anchoring of the expandable conduit to the second conduit. 
   The first conduit is typically an expandable conduit. 
   The first or expandable conduit may comprise any type of expandable conduit that is capable of sustaining plastic and/or elastic deformation. The first conduit typically comprises an expandable liner, casing or the like. The second conduit may comprise any type of conduit. The second conduit typically comprises a liner, casing, borehole or the like. 
   The inflatable device typically comprises an inflatable balloon-type portion coupled to a ring. This allows a string or the like to be passed through the inflatable device in use. 
   Optionally, the inflatable device includes an expander device. The expander device is optionally telescopically coupled to the inflatable device, so that when the expander device is moved a certain distance, the inflatable device is deflated and subsequently moves with the expander device. 
   Alternatively, the expandable device may be releasably attached to the inflatable device, typically using a latch mechanism. 
   The inflatable device may be located within the expandable conduit. Alternatively, the inflatable device may be coupled at or near an upper end of the expandable conduit, or at or near a lower end of the expandable conduit. The inflatable device may be coupled to the expandable conduit using any suitable connection. 
   The inflatable device is typically inflated to expand the expandable conduit whereby the expandable conduit contacts the second conduit, thereby providing an anchor. In this embodiment, the expandable conduit is optionally provided with a slotted portion to facilitate expansion. This is advantageous as the contact between the expandable conduit and the second conduit provides the anchor, and forces applied to the expandable conduit are mainly channelled into the second conduit via the expandable conduit and not the inflatable device. 
   Alternatively, the inflatable device is inflated whereby a portion thereof directly contacts the second conduit to provide an anchor. 
   The expander device is typically manufactured from steel. Alternatively, the expander device may be manufactured from ceramic, or a combination of steel and ceramic. The expander device is optionally flexible. 
   The expander device is optionally provided with at least one seal. The seal typically comprises at least one O-ring. 
   The method optionally comprises one, some or all of the additional steps of inserting an expander device into the expandable conduit, operating the expander device to expand the expandable conduit, deflating the inflatable device, and removing the expander device and/or the inflatable device from the expandable conduit and/or the second conduit. 
   The method optionally comprises one, some or all of the additional steps of attaching an expander device to the inflatable device, operating the expander device to expand the expandable conduit, re-attaching the expander device to the inflatable device, deflating the inflatable device, and removing the expander device and/or the inflatable device from the expandable conduit and/or second conduit. 
   The expander device is typically operated by propelling it through the expandable conduit using fluid pressure. Alternatively, the expander device may be operated by pigging it along the expandable conduit using a conventional pig or tractor. The expander device may also be operated by propelling it using a weight (from the string for example), or may by pulling it through the expandable conduit (e.g. using drill pipe, rods, coiled tubing, a wireline or the like). 
   Optionally, the inflatable device may act as a seal whereby fluid pressure can be applied below the seal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention shall now be described, by way of example only, with reference to the accompanying drawings, in which: 
       FIGS. 1   a  to  1   d  are successive stages in anchoring and expanding an expandable conduit within a second conduit using a first embodiment of an inflatable device; 
       FIGS. 2   a  to  2   d  are successive stages in anchoring and expanding an expandable conduit within a borehole to tie back the expandable conduit to a casing using a second embodiment of an inflatable device; 
       FIGS. 3   a  to  3   d  are successive stages in anchoring and expanding an expandable conduit within a second conduit using a third embodiment of an inflatable device; 
       FIG. 4   a  is a front elevation showing a first configuration of a friction and/or sealing material that can be applied to an outer surface of the conduits shown in  FIGS. 1  to  3 ; 
       FIG. 4   b  is an end elevation of the friction and/or sealing material of  FIG. 4   a;    
       FIG. 4   c  is an enlarged view of a portion of the material of  FIGS. 4   a  and  4   b  showing a profiled outer surface; 
       FIG. 5  is a schematic cross-section of an expandable conduit that can be used with the present invention having an alternative configuration of a friction and/or sealing material; 
       FIG. 6   a  is an front elevation of the friction and/or sealing material of  FIG. 5 ; and 
       FIG. 6   b  is an end elevation of the friction and/or sealing material of  FIG. 6   a.   
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , there is shown in sequence ( FIGS. 1   a  to  1   d ) successive stages of anchoring an expandable conduit  10  to a casing  12  provided in a borehole (not shown), the borehole typically being drilled to facilitate the recovery of hydrocarbons. The expandable conduit  10  is typically an expandable liner or casing, but any type of expandable conduit may be used. 
   The borehole is conventionally lined with casing  12  to prevent the formation around the borehole from collapsing and also to prevent unwanted fluids from the surrounding formation from flowing into the borehole, and similarly, prevents fluids from within the borehole escaping into the surrounding formation. It should be noted that the casing  12  may comprise any type of conduit, such as a pipeline, a liner, a casing, a borehole or the like. 
   An inflatable device  14 , that in this embodiment has an expander device  16  telescopically attached thereto, is positioned within the expandable conduit  10  before the conduit  10  is inserted into the casing  12 . 
   Referring to  FIG. 1   a , the conduit  10  with the inflatable device  14  and expander device  16  located therein is run into the hole to the required setting depth. As can be seen in  FIG. 1   a , a lower end  10   l  of the expandable conduit  10  is radially expanded (indicated generally at  18 ) to allow the inflatable device  14  and the expander device  16  to be located therein. It will be appreciated that although  FIGS. 1   a  to  1   d  show the inflatable device  14  and expander device  16  located at or near the lower end  10   l  of the conduit  10 , the inflatable device  14  and/or the expander device  16  may also be located at or near an upper end of the conduit  10 . In this case, the expander device  16  is propelled downwardly using, for example, the weight of a string, fluid pressure or any other conventional method. 
   The inflatable device  14  may be of any suitable configuration, but is typically a device that has an inflatable annular balloon-type portion  14   b  that is mounted on an annular ring  14   r . The annular ring  14   r  allows a string, wireline or the like to be passed through the inflatable device  14  as required. This is particularly advantageous where the inflatable device  14  is positioned at the upper end of the conduit  10 . Thus, substantially full-bore access is still possible. 
   Referring to  FIG. 1   b , the inflatable device  14  is inflated to expand the inflatable annular balloon-type portion  14   b . As the balloon-type portion  14   b  expands, an anchor portion  10   a  of the conduit  10  is also expanded. The anchor portion  10   a  is expanded by the inflatable device  14  until it contacts the casing  12 , as shown in  FIG. 1   b . This contact between the anchor portion  10   a  of the expandable conduit  10  and casing  12  provides an anchor point and/or a seal between the expandable conduit  10  and the casing  12 . The outer surface of the anchor portion  10   a  may be suitably profiled (e.g. ribbed) or coated with a friction and/or sealing material  100  ( FIGS. 4   a  to  4   c ) to enhance the grip of the conduit  10  on the casing  12 . The friction and/or sealing material  100  may comprise, for example, any suitable type of rubber or other resilient materials. It should be noted that the friction and/or sealing material  100  can be provided on an outer surface  10   s  of the conduit  10  at various axially spaced-apart locations. 
   Referring to  FIGS. 4   a  to  4   c , the friction and/or sealing material  100  typically comprises first and second bands  102 ,  104  that are axially spaced apart along a longitudinal axis of the conduit  12 . The first and second bands  102 ,  104  are typically axially spaced by some distance, for example 3 inches (approximately 76 mm). 
   The first and second bands  102 ,  104  are preferably annular bands that extend circumferentially around the anchor point  10   a  of the conduit  10 , although this configuration is not essential. The first and second bands  102 ,  104  typically comprise 1 inch wide (approximately 25.4 mm) bands of a first type of rubber. The friction and/or sealing material  100  need not extend around the full circumference of the conduit  10 . 
   Located between the first and second bands  102 ,  104  is a third band  106  of a second type of rubber. The third band  106  preferably extends between the first and second bands  102 ,  104  and is thus typically 3 inches (approximately 76 mm) wide. 
   The first and second bands  102 ,  104  are typically of a first depth. The third band  106  is typically of a second depth. The first depth is optionally larger than the second depth, although they are typically the same, as shown in  FIG. 4   a . The first and second bands  102 ,  104  may protrude further from the surface  10   s  than the third band  106 , although this is not essential. 
   The first type of rubber (i.e. first and second bands  102 ,  104 ) is preferably of a harder consistency than the second type of rubber (i.e. third band  106 ). The first type of rubber is typically 90 durometer rubber, whereas the second type of rubber is typically 60 durometer rubber. Durometer is a conventional hardness scale for rubber. 
   The particular properties of the rubber may be of any suitable type and the hardnessess quoted are exemplary only. It should also be noted that the relative dimensions and spacings of the first, second and third bands  102 ,  104 ,  106  are exemplary only and may be of any suitable dimensions and spacing. 
   As can be seen from  FIG. 4   c  in particular, an outer face  106   s  of the third band  106  can be profiled. The outer face  106   s  is ribbed to enhance the grip of the third band  106  on an inner face  12   i  of the casing  12 . It will be appreciated that an outer surface on the first and second bands  102 ,  104  may also be profiled (e.g. ribbed). 
   The two outer bands  102 ,  104  being of a harder rubber provide a relatively high temperature seal and a back-up seal to the relatively softer rubber of the third band  106 . The third band  106  typically provides a lower temperature seal. 
   Referring to  FIG. 5 , there is shown an alternative conduit  120  that can be used in place of conduit  10 . Conduit  120  is substantially the same as conduit  10 , but is provided with a different configuration of friction and/or sealing material  122  on an outer surface  120   s.    
   The expandable conduit  120  is provided with a pre-expanded portion  120   e  in which an expander device (e.g. expander device  16 ) and/or an inflatable device (e.g. device  14 ) may be located whilst the conduit  120  is run into a borehole or the like. It should be noted that the expander device need not be located in the conduit  120  whilst it is being run into the borehole, and can be located in the conduit  120  once it is in place. 
   As shown in  FIG. 5 , the expandable conduit  120  is provided with the friction and/or sealing material  122  at at least one location. The friction and/or sealing material  122  is applied to the outer surface  120   s  of the conduit  120  at axially spaced apart locations, typically spaced from one another by around 12 inches (approximately 305 mm). 
   The friction and/or sealing material  122  is best shown in  FIGS. 6   a  and  6   b . The friction and/or sealing material  122  is in the form of a zigzag. In this embodiment, the friction and/or sealing material  122  comprises a single (preferably annular) band of rubber that is, for example, of 90 durometers hardness and is about 2.5 inches (approximately 28 mm) wide by around 0.12 inches (approximately 3 mm) deep. 
   To provide a zigzag pattern and hence increase the strength of the grip and/or seal that the formation  150  provides in use, a number of slots  124   a ,  124   b  (e.g. 20) are milled into the band of rubber. The slots  124   a ,  124   b  are typically in the order of 0.2 inches (approximately 5 mm) wide by around 2 inches (approximately 50 mm) long. 
   To create the zigzag pattern, the slots  124   a  are milled at around 20 circumferentially spaced-apart locations, with around 18° between each along one edge  122   a  of the band. The process is then repeated by milling another 20 slots  124   b  on the other side  122   b  of the band, the slots  124   b  on side  122   b  being circumferentially offset by 9° from the slots  124   a  on the other side  122   a.    
   In use, the friction and/or sealing material  122  is applied to the outer surface  120   s  of the (unexpanded) expandable conduit  120 . It should be noted that the configuration, number and spacing of the friction and/or sealing material.  122  can be chosen to suit the particular application. 
   It should be noted that forces applied to the conduit  10 ,  120  e.g. by subsequent movement of the conduit  10 ,  120  that is by pushing or pulling on the conduit  10 ,  120  for example, will be mainly transferred to the casing  12  via the anchor point and not through the inflatable device  14 . This is advantageous as it reduces the risk of damage to the inflatable device  14 . Additionally, this also reduces the risk of damage to the casing  12  that may have occurred where a conventional slip is used. Also, conventional slips may lose their grip on the casing  12  where damage ensues or the casing  12  is weak. Transferring substantially all of the forces directly to the casing  12  via the anchor point obviates these disadvantages. 
   The expander device  16  can then be pulled through the expandable conduit  10 ,  120  to radially expand the conduit  10 ,  120  as shown in  FIG. 1   c . The expander device  16  can be propelled through the conduit  10 ,  120  in any conventional manner. In  FIG. 1 , the expander device  16  is pulled through the conduit  10 ,  120  using a string  20  that is attached to the expander device  16  in any conventional manner. 
   In the embodiment shown in  FIG. 1 , the expander device  16  is telescopically coupled to the inflatable device  14  using a telescopic coupling, generally indicated at  22 . Coupling  22  comprises one or more telescopically coupled members  24  that are attached to the inflatable device  14 . As the expander device  16  is pulled upwards, the telescopic coupling  22  extends a certain distance, say 10 feet (approximately 3 meters), at which point the telescopic member(s)  24  are fully extended. At this point, the inflatable balloon-type portion  14   b  is automatically deflated and further upward movement of the expander device  16  causes the inflatable device  14  also to move upward, as shown in  FIG. 1   d.    
   It should be noted that the inflatable device  14  is no longer required to anchor the conduit  10 ,  120  to the casing  12  as the expanded conduit  10  ( FIGS. 1   c  and  1   d ) secure the (expanded and unexpanded) conduit  10 ,  120  to the casing  12 . The friction and/or sealing material  100 ,  122  is used to enhance the grip of the conduit  10 ,  120  on the casing  12  in use, and can also provide a seal in an annulus created between the conduit  10 ,  120  and the casing  12 . 
   The expander device  16  is continually pulled upwards towards the surface until the expandable conduit  10 ,  120  is fully expanded to contact the casing  12 . Thereafter, the inflatable device  14  and the expander device  16  may be removed from the expandable conduit  10 ,  120  and/or the casing  12  at the surface. 
   Anchoring and expanding the expandable conduit  10 ,  120  in this way has several advantages. With the embodiment shown in  FIG. 1 , it is possible to deploy a control line or coiled tubing to control operation of the inflatable device  14  and any other apparatus located in the borehole, and a control line, wireline or coiled tubing may be used to propel or pull the expander device  16 . With the embodiment shown in  FIG. 1 , there is no pressure exposure to the surrounding formation and no rig is required. With the inflatable device  14  configured as an annular ring  14   r , substantially full bore access is still possible. 
   It should be noted that the method described with reference to  FIG. 1  is intended to expand the expandable conduit  10 ,  120  in a single pass of the expander device  16  through the expandable conduit  10 ,  120 , but multiple passes and/or expansions are possible. 
   Referring to  FIG. 2 , there is shown in sequence ( FIGS. 2   a  to  2   d ) successive stages of hanging an expandable conduit  30  off a casing  32  (ie tying back a liner), the expandable conduit  30  typically comprising an expandable liner and being used to line or case a lower portion of a borehole  34 , the borehole  34  typically being drilled to facilitate the recovery of hydrocarbons. The lower portion of the borehole  34  has not been lined/cased, wherein the upper portion of the borehole  34  has been lined with an existing casing or liner  36 . 
   In the embodiment shown in  FIG. 2 , the expandable conduit  30  is provided with a friction and/or sealing material  38  on an outer surface thereof. The function of the friction and/or sealing material  38  is to provide a (friction and/or sealing) coupling between the expandable conduit  30  and the existing liner or casing  36 . The friction and/or sealing material  38  may also provide a seal between the lower (unlined) and upper (lined) portions of the borehole  34  The friction and/or sealing material may comprise, for example, any suitable type of rubber or other resilient materials. For example, the friction and/or sealing material  38  can be configured in a similar way to the friction and/or sealing material  100 ,  122  described above with reference to  FIGS. 4  to  6 . 
   Additionally, the conduit  30  may be provided with friction and/or sealing material (e.g. material  100 ,  122 ) at a lower end  30   l  of the conduit  30  to enhance the anchoring effect at this portion of the conduit. Additionally, the friction and/or sealing material can be provided at various spaced-apart locations along the length of the conduit  30  to enhance the coupling between the conduit  30  and the borehole  34  or casing.  36 . 
   Referring to  FIG. 2 , an inflatable device  40 , that has an expander device  42  releasably attached thereto, is positioned within the expandable conduit  30  before the conduit  30  is inserted into the borehole  34 . The conduit  30  is provided with an expandable portion of casing or liner  44 , portion  44  being provided with a plurality of longitudinal slots  48 . The portion  44  may be located at a lower end  30   l  of the conduit  30  or may be integral therewith. 
   Referring to  FIG. 2   a , the conduit  30  with the inflatable device  40  and expander device  42  releasably attached at or near a lower end thereof, is run into the borehole  34  to the required setting depth. As can be seen in  FIG. 2   a , a lower end  30   l  of the conduit  30  is radially expanded (indicated generally at  50 ) to allow the expander device  42  to be located therein. It will be appreciated that although  FIGS. 2   a  to  2   d  show the inflatable device  40  and expander device  42  located at or near the lower end  30   l  of the conduit  30 , the inflatable device  40  and/or the expander device  42  may also be located at or near an upper end of the conduit  30 . In this case, the expander device  42  is propelled downwardly using, for example, the weight of a string, fluid pressure or any other conventional method. 
   The inflatable device  40  may be of any suitable configuration, but is typically a device that has an inflatable annular balloon-type portion  40   b  that is mounted on an annular ring  40   r . The annular ring  40   r  allows a string, wireline or the like to be passed through the inflatable device  40  as required. This is particularly advantageous where; the inflatable device  40  is positioned at the upper end of the conduit  30 . 
   Referring to  FIG. 2   b , the inflatable device  40  is inflated to expand the inflatable annular balloon-type portion  40   b . As the balloon-type portion  40   b  expands, the expandable portion  44  of conduit  30  also expands. As can be seen in  FIG. 2   b , the longitudinal slots  48  widen as the portion  44  expands. Portion  44  acts as an anchor for the casing  30  and is expanded until it contacts the borehole  34 , as shown in  FIG. 2   b . This contact between portion  44  and the borehole  34  provides an anchor point and/or a seal between the expandable conduit  30  (to which portion  44  is attached or integral therewith) and the borehole  34 . 
   As with the previous embodiment, the expander device  42  is then pulled through the expandable conduit  30  to radially expand the conduit  30 , as shown in  FIG. 2   c . The expander device  42  can be propelled through the conduit  30  in any conventional manner. In  FIG. 2 , the expander device  42  is pulled through the conduit  30  using a drill pipe or string  52  that is attached to the expander device  42  in any conventional manner. 
   As the expander device  42  is pulled upwards, the upward movement thereof is stopped after a predetermined time or distance, at which point the expander device  42  is lowered until a coupling between the expander device  42  and the inflatable device  40  latches. As with the previous embodiments, the inflatable annular balloon-type portion  40   b  is automatically deflated and further upward movement of the expander device  42  causes the inflatable device  40  also to move upward, as shown in  FIG. 2   d . It should be noted that the upward movement of the expander device  42  should only be stopped once a sufficient length of conduit  30  has been expanded to provide a sufficient anchor. 
   It should also be noted that the portion  44  is no longer required to anchor the conduit  30  to the borehole  34  as the expanded conduit  30  ( FIGS. 2   c  and  2   d ) secures the conduit  30  to the borehole  34 . The friction and/or sealing material (where used) can help to provide a reliable anchor for the conduit  30  whilst it is being expanded and also when in use. 
   The expander device  42  is continually pulled upwards until the conduit  30  is fully expanded, as shown in  FIG. 2   d  Thereafter, the inflatable device  40  and the expander device  42  may be removed from the expandable conduit  30  and the borehole at the surface. As shown in  FIG. 2   d , the conduit  30  expands whereby the friction and/or sealing material  38  contacts the casing  36 . This provides a tie back to the casing  36  and optionally a seal between the upper (lined) portion of the wellbore and the lower (lined) borehole  34 , depending upon the composition of the material  38 . 
   With the embodiment shown in  FIG. 2 , there is no pressure exposure to the formation, full bore access is still possible, the conduit  30  may be expanded in a single pass (multiple passes possible) and it may be used to anchor and set in an open hole. Additionally, it provides a tie back to the casing  36  in a single pass of the expander device  42 . It should be noted that the method described with reference to  FIG. 2  is intended to tie back the casing in a single pass, but multiple passes and/or expansions are possible. 
   It should also be noted that successive lengths of expandable conduit may be coupled to casings or liners thereabove using the same method. Thus, the method(s) described herein may be used to line or case a borehole without the use of cement. 
   Referring to  FIG. 3 , there is shown in sequence ( FIGS. 3   a  to  3   d ) successive stages of anchoring an expandable conduit  80  to a casing  82  provided in a borehole (not shown), the borehole typically being drilled to facilitate the recovery of hydrocarbons. 
   An inflatable device  84  is releasably attached to a lower end  80   l  of the expandable conduit  80  before the conduit  80  is inserted into the casing  82 . The expander device  86  is located within the lower end  80   l  of the conduit  80 , the lower end  80   l  being expanded to accommodate the expander device  86 . Similar to the previous embodiment, the inflatable device  84  has the expander device  86  releasably coupled thereto via a coupling  88 . Otherwise, the inflatable device  84  and the expander device  86  are substantially the same as the previous embodiments. 
   Referring to  FIG. 3   a , the casing  80  with the inflatable device  84  attached thereto and the expander device  86  located therein is run into the hole to the required setting depth. It will be appreciated that although  FIGS. 3   a  to  3   d  show the inflatable device  84  releasably attached to the lower end  80   l  of the conduit  80 , the inflatable device  84  may be releasably attached at or near an upper end of the conduit  80 . 
   The inflatable device  84  may be of any suitable configuration, but is typically a device that has an inflatable annular balloon-type portion  84   b  that is mounted on an annular ring  84   r . The annular ring  84   r  allows a string, wireline or the like to be passed through the inflatable device  84  as required. This is particularly advantageous where the inflatable device  84  and/or the expander device  86  are positioned at the upper end of the conduit  80 . 
   Referring to  FIG. 3   b , the inflatable device  84  is inflated to expand the inflatable annular balloon-type portion  84   b . As the balloon-type portion  84   b  expands, it contacts the casing  82 , thus providing an anchor between the conduit  80  and the casing  82 . This contact between the balloon-type portion  84   b  and the casing  82  provides an anchor point and/or a seal between the conduit  80  and the casing  82 . 
   It should be noted that in this embodiment, the forces applied to the conduit  80  by subsequent movement of the conduit  80 , that is by pushing or pulling on the conduit  80  for example, will be transferred to the casing  82  via the inflatable device  84 . However, unlike conventional slips, the inflated balloon-type portion  84   b  is less likely to damage the casing. Additionally, the size of the balloon-type portion  84   b  can be chosen whereby it is sufficiently large so as not to lose its grip on the casing  82 , even when the inflatable device  84  is moved upwardly or downwardly. 
   The expander device  86  is pulled through the expandable conduit  80  to radially expand the conduit  80 , as shown in  FIG. 3   c . The expander device  86  can be propelled through the conduit  80  in any conventional manner, as with the previous embodiments. 
   Also, and as with the previous embodiments, an outer surface  80   s  of the conduit  80  can be provided with a friction and/or sealing material. The friction and/or sealing material may comprise, for example, any suitable type of rubber or other resilient materials. For example, the friction and/or sealing material can be configured in a similar way to the friction and/or sealing material  100 ,  122  described above with reference to  FIGS. 4  to  6 . 
   Additionally, the conduit  80  may be provided with friction and/or sealing material (e.g. material  100 ,  122 ) at a lower end  80   l  of the conduit  80  to enhance the anchoring effect at this portion of the conduit  80 . Additionally, the friction and/or sealing material can be provided at various spaced-apart locations along the length of the conduit  80  to enhance the coupling between the conduit  60  and the casing  82 . 
   As the expander device  86  is pulled upwards, the upward movement thereof is stopped after a predetermined time or distance, at which point the expander device  84  is lowered until the coupling  88  between the expander device  86  and the inflatable device  86  latches. As with the previous embodiments, the inflatable balloon-type portion  84   b  is automatically deflated and further upward movement of the expander device  86  causes the inflatable device  84  also to move upward, as shown in  FIG. 3   d . It should be noted that the upward movement of the expander device  86  should only be stopped once a sufficient length of conduit  80  has been expanded to provide a sufficient anchor. 
   The expander device  86  is continually pulled upwards towards the surface until the conduit  80  is fully expanded to contact the casing  82 . Thereafter, the inflatable device  84  and the expander device  86  may be removed from the borehole at the surface. 
   Anchoring and expanding the conduit  80  in this way has the same advantages as in the previous embodiment, but the  FIG. 3  embodiment is designed to anchor and set in cased hole rather than open hole. 
   The method and apparatus described herein may be used for a plurality of different downhole functions relating to the use of expandable conduit. For example, they may be used where the original liner or casing requires to be repaired due to damage or the like by overlaying the damaged portion with a portion of expandable conduit. They may also be used to tie back to the liner or casing, as described herein. 
   Thus, there is provided in certain embodiments an apparatus and method of anchoring an expandable conduit to a second conduit. The apparatus and method of certain embodiments provide numerous advantages over conventional mechanical anchoring devices, such as slips, particularly by reducing the potential damage to conduits that mechanical slips may cause. Certain embodiments of apparatus and methods involve the use of an inflatable device that can either be a) attached directly at or near the top or bottom of the expandable conduit, or b) placed within the top or bottom of the expandable conduit. In a), anchoring forces are generated as a result of friction between the inflatable device and the second conduit, the forces being passed into the conduit via the inflatable device. In b), anchoring forces are generated by friction between an outer surface of the expandable conduit and the second conduit, the forces being substantially passed into the second conduit directly via the expandable conduit. The outer surface of the expandable conduit may be suitably prepared (ie provided with a friction enhancing material) to increase the strength of the anchor. 
   Modifications and improvements may be made to the foregoing without departing from the scope of the present invention.