AU2014327755A1

AU2014327755A1 - Sealing insert and method

Info

Publication number: AU2014327755A1
Application number: AU2014327755A
Authority: AU
Inventors: Neil Anderson; Colin Mackie
Original assignee: Swellfix BV
Current assignee: Swellfix BV
Priority date: 2013-09-30
Filing date: 2014-07-29
Publication date: 2016-02-18
Also published as: GB2518683B; CA2923107A1; EP3052744A2; GB201317280D0; WO2015043801A2; GB2518683A; US20160208569A1; WO2015043801A3

Abstract

A method for sealing a side pocket of a downhole mandrel in a tubing string comprises retrieving a cartridge component from the side pocket of the downhole mandrel and then deploying a sealing insert into the side pocket of the downhole mandrel,wherein the sealing insert comprises a swellable sealing element on an outer surface thereof. The swellable sealing element swells to provide a seal within the side pocket. A sealing insert for use in sealing a side pocket of a downhole mandrel, comprises a base member and a swellable sealing element mounted on the outer surface of the base member and configured to swell when exposed to an activator. The sealing insert is geometrically configured to permit insertion within a side pocket of a downhole mandrel such that when the sealing element is swollen said sealing element provides a seal within said side pocket.

Description

WO 2015/043801 PCT/EP2014/066294 1 SEALING INSERT AND METHOD FIELD OF THE INVENTION The present invention relates to a method for sealing a side pocket in a 5 downhole mandrel, such as a downhole gas-lift mandrel. The present invention also relates to a sealing insert for use in sealing a side pocket in a downhole mandrel. BACKGROUND TO THE INVENTION In the oil and gas industry wellbores are drilled from surface to intercept 10 subterranean reservoirs, and used to provide a communication path for reservoir fluids, such as oil and gas, to flow to surface. The natural reservoir pressure may allow unaided production of the reservoir fluids to surface. However, in some cases the reservoir pressure may be insufficient to support natural production of reservoir fluids, for example where the pressure is naturally low, or where pressure has diminished 15 over a period of time. To address such cases it is has become known for operators to utilise artificial lift techniques. There are many known artificial lift techniques in common use, such as gas lift. Gas lift involves introducing a gas at one or more points along the wellbore production tubing to reduce the density of the well fluids and thus allow the reservoir pressure to 20 lift the fluids out of the production tubing. Gas lift may be used in either liquid (e.g., oil) or gas wells. To facilitate gas lift an operator will include a gas lift mandrel within the production tubing string, which thus forms a permanent component of the completion. The gas lift mandrel includes a side port which provides fluid communication between 25 the production tubing and the surrounding annulus. The gas lift mandrel typically also includes a side pocket which receives a gas lift valve, wherein the gas lift valve is sealingly engaged within the side pocket, for example via chevron seals, and provides selective control of fluid through the side port. Normally, the gas lift valve is provided in the form of a one way valve, in that fluid communication is only permitted into the 30 production tubing, with outflow from the production tubing into the surrounding annulus prevented. In use, whenever gas lift is required an operator will inject pressurised gas into the wellbore annulus, and into the production tubing via the gas lift mandrel and valve arrangement. 35 US 2005/0061369 discloses a mandrel for a gas lift valve.

WO 2015/043801 PCT/EP2014/066294 2 There is a risk that the gas lift mandrel could become damaged or corroded, for example particularly in the region of the side port. In some cases such damage or corrosion could compromise the ability of the gas lift valve to prevent outflow of fluids from the production fluid and into the annulus, resulting in possible uncontrolled 5 pressurisation of the annulus, leading to a well control failure. In such cases it may be necessary to temporarily kill the well, and undertake a complete workover program to pull the entire completion and replace the faulty gas lift mandrel. The costs of such a workover program can be prohibitive, such that in many cases an operator may decide to abandon the well altogether. 10 Many other downhole components may include a form of side pocket mandrel (for example, WO 2013/138896 discloses a cementing stage tool with a side pocket), which may also suffer from similar problems with damage or corrosion leading to a well control issues. For example, a downhole chemical injection valve will typically include a side pocket for accommodating a chemical injection valve. Further, some downhole 15 valves, such as a downhole tubing valve, include a side pocket for accommodating a control valve which is used to operate the downhole valve. SUMMARY OF THE INVENTION An aspect of the present invention relates to a method for sealing a side pocket 20 of a downhole mandrel in a tubing string, comprising: retrieving a cartridge component from the side pocket of the downhole mandrel; deploying a sealing insert into the side pocket of the downhole mandrel, wherein the sealing insert comprises a swellable sealing element on an outer surface thereof; and 25 swelling the swellable sealing element to provide a seal within the side pocket. The seal within the side pocket achieved by the sealing insert may function to substantially prevent any fluid communication outwardly or inwardly of the downhole mandrel via said side pocket. Such an arrangement may be used to prevent undesired fluid transfer between the downhole mandrel and surrounding environment. 30 The sealing insert may be used to address any damage to one or both of the mandrel side pocket and the cartridge component. Such damage may otherwise prevent the side pocket and/or cartridge component from providing a necessary fluid control when said cartridge component is in place. For example, damage to one or both of the side pocket and cartridge component may define or create a leak path 35 which may establish uncontrolled fluid communication to/from the downhole mandrel.

WO 2015/043801 PCT/EP2014/066294 3 The method may comprise sealing a side pocket of a downhole mandrel which has become damaged, for example by corrosion, by other wellbore operations or the like. In such an arrangement the sealing insert may function to seal any regions of damage, such as corroded regions, within the side pocket of the mandrel. This may 5 therefore prevent such damaged regions providing or continuing to provide any potential leak paths. The ability to address any damage to the downhole mandrel in accordance with the present invention may provide significant advantages in that any requirement to retrieve the entire downhole mandrel, and the associated tubing string, may be 10 prevented. However, although the present invention has application in addressing situations where the downhole mandrel has become damaged, the method may nevertheless be used in other occasions, such as when an operator may wish to disable an existing and normally functioning downhole mandrel. 15 The downhole mandrel may comprise a side port which communicates with the side pocket. The cartridge component, during normal use and prior to being retrieved, may be configured to cooperate with the side pocket of the downhole mandrel to control fluid communication through the side port. In the event of failure or damage of one or both of the cartridge component and side pocket of the mandrel, such fluid 20 control may be compromised. In such an arrangement the sealing insert may function to seal said side port, and thus prevent any subsequent communication with the side pocket and the tubing string associated with the downhole mandrel. The method may comprise sealing a side pocket which has become damaged in the region proximate or adjacent to the side port. 25 The side port of the downhole mandrel may be arranged to communicate with an annulus surrounding the downhole mandrel. Such an annulus may be defined between the mandrel and a bore wall, such as a wall of a casing string, liner string, open hole or the like. In such an arrangement the sealing insert may function to substantially prevent any fluid communication between the annulus and the downhole 30 mandrel. The side port of the downhole mandrel may be arranged to communicate with a fluid conduit, such as an injection conduit or line which may extend from the downhole mandrel to surface level. In such an arrangement the sealing insert may function to substantially prevent any fluid communication between the fluid conduit and the 35 downhole mandrel.

WO 2015/043801 PCT/EP2014/066294 4 The sealing element may extend along a desired length of the side pocket to established sealing therein. The sealing element may extend along a sufficient length to span the side port. The sealing element may extend along a sufficient length to span damaged or corroded areas within the side pocket. 5 The downhole mandrel may comprise any downhole mandrel comprising a side pocket. In such an arrangement the cartridge may comprise any cartridge which may be utilised within the side pocket of any downhole mandrel In one embodiment the downhole mandrel may comprise or define a gas lift mandrel. In such an arrangement the cartridge component may comprise or define a 10 gas lift valve. In one embodiment the downhole mandrel may comprise or define a chemical injection mandrel. In such an arrangement the cartridge component may comprise or define a chemical injection valve. In one embodiment the downhole mandrel may comprise or define a downhole 15 valve mandrel, such as a tubing safety valve mandrel, downhole safety valve mandrel or the like. In such an arrangement the cartridge component may comprise or define a control cartridge for use in providing control to the associated downhole valve. For example, in such an arrangement the cartridge component may comprise or define a control valve. 20 The sealing insert may be of the same general geometrical form as the cartridge component being retrieved. Such an arrangement may permit the sealing insert to be readily received within the side pocket of the downhole mandrel. The downhole mandrel may be connected in-line with the tubing string. The downhole mandrel may comprise connectors, such as threaded connectors, at 25 opposing ends to facilitate in-line connection with the tubing string. The tubing string may define a production tubing string. The tubing string may be arranged for the production of fluids from a subterranean reservoir. The tubing string may be arranged for the production of a gas from a subterranean reservoir. The tubing string may be arranged for the production of liquids, such as oil, from a 30 subterranean reservoir. The tubing string may define an injection tubing string. The tubing string may be arranged for the injection of fluids, such as a liquid (e.g., water) or gas into a subterranean reservoir. The method may comprise retrieving the cartridge component through the 35 tubing string. The method may comprise retrieving the cartridge component to surface.

WO 2015/043801 PCT/EP2014/066294 5 The method may comprise retrieving the cartridge component via a conveyance arrangement. The conveyance arrangement may comprise an elongate line, such as wireline, slickline or the like. The conveyance arrangement may comprise coiled tubing. 5 The method may comprise establishing a connection between the conveyance arrangement and the cartridge component. The method may comprise releasing the cartridge component from the side pocket, for example by disabling a latch mechanism, overcoming an interference force or the like. 10 The method may comprise deploying the sealing insert through the tubing string. The method may comprise deploying the sealing insert from surface. The method may comprise deploying the sealing insert via a conveyance arrangement. The conveyance arrangement may be the same or similar to the conveyance arrangement used to retrieve the cartridge component. The conveyance 15 arrangement may comprise an elongate line, such as wireline, slickline or the like. The conveyance arrangement may comprise coiled tubing. The method may comprise releasing a connection between the conveyance arrangement and the sealing insert when said sealing insert is located within the side pocket of the mandrel. 20 The method may comprise securing the sealing insert within the side pocket of the downhole mandrel. The method may comprise mechanically latching the sealing insert within the side pocket of the mandrel. The method may comprise securing the sealing insert within the side pocket of the mandrel via the swelling element after sealing has been established. For example, the sealing element may provide an 25 interference force within the side pocket of the mandrel. The method may comprise preventing or restricting flow along the tubing string prior to retrieving the cartridge component. For example, the method may comprise ceasing production or injection along the tubing string. This may be achieved via well control equipment, such as a production or injection tree, sub surface valve, well kill 30 fluid or the like, or any suitable combination. The method may comprise setting a barrier downhole of the mandrel. The method may comprise setting a barrier within the tubing string downhole of the mandrel. Such a barrier may be set by closing a valve within the tubing string. The barrier may be set by installing a plug within the tubing string. The plug may be WO 2015/043801 PCT/EP2014/066294 6 deployed on a conveyance arrangement, such as on wireline, slickline, coiled tubing or the like. The method may comprise removing the barrier set within the tubing string, for example after the sealing insert has established a seal within the side pocket of the 5 mandrel. Such an arrangement may permit subsequent production and/or injection operations to be achieved using the tubing string which now incorporates a sealed mandrel. The method may comprise flowing or placing a fluid into the tubing string. Such a fluid may be placed above a barrier set within the tubing string. Such a fluid may be 10 placed in the tubing string before or after the sealing insert is located within the side pocket of the mandrel. A fluid placed within the tubing string may be utilised to establish a desired hydrostatic pressure therein. Such hydrostatic pressure may be used to contain well pressure. Such an arrangement may have particular application where the tubing 15 string has previously been used to produce a gas from or inject gas into a subterranean formation. A fluid placed within the tubing string may be utilised to provide a desired swelling activator for the swellable sealing element. The method may comprise setting a barrier within an annulus surrounding at 20 least a portion of the tubing. Such an annulus barrier may be set via one or more packers or the like. The method may comprise subsequently removing the barrier from the annulus, for example after the sealing insert has provided a seal within the side pocket of the mandrel. The method may comprise flowing or placing a fluid into the annulus. Such a 25 fluid may be placed above a barrier set within the annulus. A fluid placed within the annulus may be utilised to establish a desired hydrostatic pressure therein. Such hydrostatic pressure may be used to provide a degree of pressure control within the annulus. A fluid placed within the annulus may be utilised to provide a desired swelling 30 activator for the swellable sealing element. The sealing element may be generally annular in form. The sealing element may be formed of or comprise a swellable material, such as a swellable elastomer material. The sealing element may be configured to swell when exposed to a swelling activator. The sealing element may be configured to swell 35 when exposed to water. The sealing element may be configured to swell when WO 2015/043801 PCT/EP2014/066294 7 exposed to a hydrocarbon fluid, such as hydrocarbon gas, oil or the like. The sealing element may be configured to swell when exposed to different swelling activators. For example, the sealing insert may be composed of or comprise different swellable materials. 5 The sealing element may be configured to provide a sufficient delayed activation period upon exposure to a swelling activator. This may allow sufficient time for an operator to deploy the sealing insert in position within the side pocket of a gas lift mandrel without interference by premature swelling. The sealing insert may comprise a base member upon which the sealing 10 element is mounted. The sealing element may be bonded to the base member. Alternatively, the sealing element may be formed as or on a sleeve which may be mounted over the base member. The base member may be elongate. The base member may be generally cylindrical in form, for example the base member may be provided in the form of a rod. 15 The base member may comprise a metal or metal alloy material. The base member may be substantially solid. The base member may comprise at least one annular recess, wherein the sealing element is received within said annular recess. When the sealing element is received within the recess and in an unswollen state, the sealing element may define 20 an outer diameter which is less than or equal to the outer diameter of the base member. Such an arrangement may assist with easier deployment of the sealing insert. In some embodiments a single annular recess is provided within the base member. Such a single annular recess may accommodate one or more sealing 25 elements. In alternative embodiments the base member may define multiple annular recesses, axially separated from each other, wherein each annular recess accommodates at least one sealing element. The base member may comprise or define a connection region, to facilitate 30 connection with a conveyance arrangement. The base member may comprise a generally conical nose portion. Such an arrangement may assist with deployment and insertion of the sealing element into the side pocket of the mandrel. The base member may comprise a unitary component.

WO 2015/043801 PCT/EP2014/066294 8 A further aspect of the present invention relates to a sealing insert for use in performing the method of any other aspect. A further aspect of the present invention relates to a sealing insert for use in sealing a side pocket of a downhole mandrel, comprising: 5 a base member; and a swellable sealing element mounted on the outer surface of the base member and configured to swell when exposed to an activator, wherein the sealing insert is geometrically configured to permit insertion within a side pocket of a downhole mandrel such that when the sealing element is swollen said 10 sealing element provides a seal within said side pocket. The sealing insert may comprise a connector portion to permit connection to a conveyance arrangement. Such a conveyance arrangement may be used to deploy the sealing arrangement downhole and into a side pocket of a mandrel. The conveyance arrangement may comprise wireline, slickline, coiled tubing or the like. 15 The base member may define a connector portion to permit connection to the conveyance arrangement. The sealing element may be generally annular in form. The sealing element may be formed or comprise a swellable material, such as a swellable elastomer material. The sealing element may be configured to swell when 20 exposed to a swelling activator. The sealing element may be configured to swell when exposed to water. The sealing element may be configured to swell when exposed to a hydrocarbon fluid, such as hydrocarbon gas, oil or the like. The sealing element may be configured to swell when exposed to different swelling activators. For example, the sealing insert may be composed of or comprise different swellable materials. 25 The sealing element may be configured to provide a sufficient delayed activation period upon exposure to a swelling activator. This may allow sufficient time for an operator to deploy the sealing insert in position within the side pocket of a gas lift mandrel without interference by premature swelling. The sealing element may be bonded to the base member. Alternatively, the 30 sealing element may be formed as or on a sleeve which may be mounted over the base member. The base member may be elongate. The base member may be generally cylindrical in form, for example the base member may be provided in the form of a rod. The base member may comprise a metal or metal alloy material. The base member 35 may be substantially solid.

WO 2015/043801 PCT/EP2014/066294 9 The base member may comprise at least one annular recess, wherein the sealing element is received within said annular recess. When the sealing element is received within the recess and in an unswollen state, the sealing element may define an outer diameter which is less than or equal to the outer diameter of the base 5 member. Such an arrangement may assist with easier deployment of the sealing insert. In some embodiments a single annular recess may be provided within the base member. Such a single annular recess may accommodate one or more sealing elements. 10 In alternative embodiments the base member may define multiple annular recesses, axially separated from each other, wherein each annular recess accommodates at least one sealing element. The base member may comprise a generally conical nose portion. Such an arrangement may assist with deployment and insertion of the sealing element into the 15 side pocket of the mandrel. The base member may comprise a unitary component. Another aspect of the present invention relates to a sealing insert for sealing a side pocket of a downhole mandrel, the sealing insert comprising: a core and a swellable material positioned on the periphery of the core; and 20 an upper sub connected to the core and having a conveyance connector for allowing connection to a conveyance running tool. A further aspect of the present invention relates to a sealed downhole mandrel, comprising: a side pocket including a side port; and 25 a sealing insert sealingly mounted within the side pocket, wherein the sealing insert includes a swollen sealing element which extends at least over the side port of the side pocket. A further aspect of the present invention relates to a method for sealing a side pocket of a downhole mandrel in a tubing string, comprising: 30 deploying a sealing insert into the side pocket of the downhole mandrel, wherein the sealing insert comprises a swellable sealing element on an outer surface thereof; and swelling the swellable sealing element to provide a seal within the side pocket. Another aspect of the present invention relates to a method for performing a 35 downhole intervention, comprising: WO 2015/043801 PCT/EP2014/066294 10 retrieving a cartridge from a side pocket of a downhole mandrel, wherein the retrieved cartridge comprises at least one seal arrangement for providing a seal between the cartridge and the side pocket of the mandrel when located therein; deploying a new cartridge which comprises at least one swellable seal 5 arrangement into the side pocket mandrel of the downhole mandrel; and swelling the at least one swellable seal arrangement to establish a seal between the new cartridge and the side pocket mandrel. In such a method the new cartridge, once in place, may perform substantially the same function as the retrieved cartridge prior to retrieval. However, the presence 10 of at least one swellable seal element on the new cartridge may assist to address any loss of sealing integrity suffered by the retrieved cartridge when originally in place. The method may comprise replacing the at least one seal arrangement of the retrieved cartridge with at least one swellable seal element, and then deploying the retrieved cartridge as the new cartridge. In such an arrangement, the retrieved 15 cartridge may be reused. The method may comprise deploying a new cartridge which is different from the retrieved cartridge. The retrieved cartridge may comprise at least one non-swelling seal arrangement. 20 The retrieved cartridge may comprise at least one chevron seal arrangement. A further aspect of the present invention relates to a downhole side pocket cartridge for installing within a side pocket of a downhole mandrel, comprising at least one swellable sealing arrangement mounted on an outer surface thereof for establishing sealing engagement within a side pocket of a downhole mandrel. 25 It should be understood that features described or presented in relation to one aspect may be used in combination with any other aspect. BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects of the present invention will now be described, by way 30 of non-limiting examples only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic illustration of a portion of a wellbore which includes a conventional gas lift mandrel during normal operation; Figure 2 is a diagrammatic illustration of the gas lift mandrel of Figure 1 following loss in sealing integrity; WO 2015/043801 PCT/EP2014/066294 11 Figures 3, 4 and 6 to 8 illustrate sequential stages of a method according to an embodiment of the present invention for sealing the gas lift mandrel of Figure 1; Figure 5 is a longitudinal cross sectional view of a sealing insert in accordance with an embodiment of the present invention for use in a method for sealing the gas lift 5 mandrel of Figure 1; and Figures 9 and 10 diagrammatically illustrate sequences in a method according to an alternative embodiment of the present invention. DETAILED DESCRIPTION OF THE DRAWINGS 10 A wellbore system, generally indicated by reference 10, is shown in Figure 1, wherein said wellbore system 10 is provided to support the production of a gas from a subterranean reservoir (not shown). The wellbore system 10 includes a drilled bore 12 within which is located a casing string 14, wherein the casing string 14 may be cemented or packed-off within the drilled bore 12. In the embodiment illustrated a 15 production tubing string 16 extends through the casing string 14 to intercept a gas production zone (not shown) of the subterranean reservoir, wherein the production tubing 16 defines an annulus 17 with the casing string 14. A gas lift mandrel 18 is installed in-line with the production tubing 16, via threaded end connectors 20, 22. The gas lift mandrel 18 includes a primary bore section 24 which is aligned with 20 the fluid communication path along the production tubing 16, and a side pocket 26 laterally off-set from the primary bore section 24. The side pocket may define an internal diameter of, for example, around 20 to 40mm. For example in some embodiments the side pocket mandrel may define an internal diameter of, for example, 25.4 mm (1"). In other embodiments the side pocket mandrel may define an internal 25 diameter of, for example, 38.1mm (1.5"). The primary bore section 24 and side pocket 26 are in fluid communication with each other. A side port 28 is formed in the side wall of the mandrel 18 and provides fluid communication between the side pocket 26 and the annulus 17. A gas lift valve cartridge 30 is mounted within the mandrel side pocket 26, and 30 includes upper and lower seals 32, 34, such as chevron seals, positioned on either side of the port 28. The seals 32, 34 provide sealing between the valve cartridge 20 and the side walls of the side pocket 26. As will be described in further detail below, the valve cartridge 30 functions to control fluid communication between the production tubing 16 and the annulus 17 via the port 28.

WO 2015/043801 PCT/EP2014/066294 12 During normal use, an operator will inject gas 38 at high pressure into the annulus 17 from surface. When the annulus gas pressure at least exceeds the gas pressure within the production tubing 16, the gas lift valve cartridge 30 will open and permit inflow of the injected gas 38 into the gas lift mandrel 18. The injected gas 38 will 5 intimately mix with the gas 40 being produced from the subterranean reservoir, with the resulting gas mixture 42 having a lower density than the produced gas 40, allowing the reservoir pressure to then drive the gas upwardly through the production tubing string 16 to surface. An operator may continuously inject gas 38, or may provide intermittent injection. The gas lift valve 30 will function as a one way valve, such that outflow of 10 gas from the gas lift mandrel 18 into the annulus 17 should normally be prevented. There are occasions, however, where the gas lift valve 30, side pocket 26 and/or side port 28 of the mandrel 18 may become damaged, for example by corrosion, such that fluid sealing and control may become lost. For example, as shown in Figure 2 the seals 34, 36 between the valve cartridge 30 and the side pocket 26 may become 15 compromised by corrosion in this region such that gas within the production tubing 16 may leak past the valve 30 and ultimately into the annulus 17. This may result in possible uncontrolled pressurisation of the annulus 17, leading to a well control failure. In some instances the fault may lie with the gas lift valve cartridge 30. In such cases it might be possible to perform a wireline based intervention operation to retrieve 20 and replace the valve cartridge 30. However, where the fault lies with the mandrel side pocket 26, either initially or through damage during a valve replacement operation, the options to the operator were heretofore either to perform a complete workover to pull and replace the entire production string 16, or abandon the wellbore 10, which will be understood by those of skill in the art to both be undesirable. The present invention 25 provides a heretofore unknown alternative to an operator, which will allow the wellbore to continue to operate. Accordingly, if an operator discovers that a gas lift mandrel has become compromised, he may utilise an embodiment of the present invention, as will now be described, initially with reference to Figure 3. An operator will initially set a plug 50 30 within the tubing string 16 below the gas lift mandrel 18, for example using a wireline deployed plug. Following this the valve cartridge 30 is picked up by wireline 52, for example via a suitable connector and running tool (not shown), and retrieved from the side pocket 26 of the mandrel 18 and towards surface. Subsequent to this, as shown in Figure 4, a sealing insert 60 according to an 35 embodiment of the present invention is deployed from surface through the production WO 2015/043801 PCT/EP2014/066294 13 tubing 16. Also, as illustrated in Figure 4, the production tubing 16 above the plug 50, and the annulus 17, are filled with a fluid 54, in this example water. It should be understood that this water may be placed into the wellbore 10 immediately following setting of the plug, and before the valve cartridge 30 is removed. The water provides a 5 column of fluid which establishes a hydrostatic pressure within the wellbore to assist in containing the lower wellbore and reservoir pressure. The water will also function to operate the sealing insert 60, as will be described in more detail below. Reference is now made to Figure 5 in which there is shown a longitudinal cross sectional view of the sealing insert 60 of Figure 4. The insert 60 includes a cylindrical 10 solid base member 62 which has a conical tip 64 at one end and a connection profile 66 at an opposite end. The connection profile 66 facilitates connection to the wireline 52 via an appropriate connector 68 and running tool 70 (all shown in broken outline). The insert 60 further comprises an annular sealing element 72 which is mounted within an annular recess 74 formed in the base member 62. The sealing 15 element comprises a swellable elastomer material which in the present exemplary embodiment is caused to swell upon exposure to water. When the sealing element 74 is in its unswollen state, the outer diameter of said sealing insert may be less than or equal to the largest outer diameter of the base member. The sealing insert 60 is deployed into the side pocket 26 of the mandrel 18, as 20 illustrated in Figure 6, with the wireline detached and retrieved to surface. Over time, exposure to the water 54 within the production tubing 16 and annulus 17 will cause the sealing element 72 of the sealing insert 60 to swell thus sealing the side pocket 26 of the mandrel 18, as illustrated in Figure 7. As illustrated, the sealing element is of sufficient length to span the side port 28 in the mandrel 18. Further, the nature of the 25 swelling material of the sealing element is such that it can readily comply with the surfaces of the side pocket 26, and will therefore also seal-off any damaged or highly corroded areas. Further, any further corrosion or damage may be accommodated by the continuous swelling, or self-healing, effect of the swelling material. Once the sealing insert is fully swollen and the side pocket 26 of the mandrel 30 18 is fully sealed, the plug 50 may be removed, as shown in Figure 8. The wellbore 10 may then recommence production, or alternatively could now be used as an injection well. In some instances an operator may recognise that a fault has occurred at the location of a gas lift mandrel 18, as illustrated in Figure 2. However, there may be 35 occasions where an operator wishes to retain the operation of the particular gas lift WO 2015/043801 PCT/EP2014/066294 14 mandrel. Embodiments of an aspect of the present invention may permit an operator to address the fault at the mandrel 18, while still maintaining its functionality. Such an exemplary embodiment will now be described with additional reference to Figures 9 and 10. 5 In this respect, when a fault is recognised, as illustrated in Figure 2, an operator may retrieve the gas lift valve cartridge 30 on wireline 52, in the same manner as shown in Figure 3. However, rather than deploying a sealing insert as in previous embodiments, the operator can, according to the present invention, deploy a new gas lift valve cartridge 30a, as illustrated in Figure 9, again on wireline 52. In this case the 10 new valve cartridge 30a comprises upper and lower swellable seals 34a, 36a at the locations previously occupied by the chevron seals 34, 36 of the retrieved cartridge 30. In some embodiments the retrieved cartridge may be reconditioned to remove the existing seals 34, 36 and replace these with new, swellable seals 34a, 36a. However, in other embodiments a different cartridge may be utilised. 15 Although the arrangement in Figure 9 does not show any fluids positioned in the tubing string 16 above the plug 50, such fluid may, nevertheless be provided, as in Figure 6. Once the new cartridge 30a is positioned within the side pocket 26 of the mandrel 18, the seals 34a, 36a may be activated to swell, thus providing sealing 20 engagement between the new cartridge 30a and the side pocket mandrel, as illustrated in Figure 10. The use of the swelling seals 34a, 36a in this case may address any previous issues with losses in seal integrity with the retrieved cartridge 30, and may allow fluid control via the side port 28 of the mandrel 18 to be retained. It should be understood that the embodiments described herein are merely 25 exemplary and that various modifications may be made thereto without departing from the scope of the invention. For example, in the embodiment illustrated the wellbore 10 supports gas production. However, in other embodiments oil production may be present, or alternatively downhole injection may be present. Further, the sealing element of the sealing insert in the illustrated embodiments is provided to swell upon 30 exposure to water. However, in other embodiments, for example where the wellbore supports oil production, the sealing element may be arranged to swell when exposed to oil. Also, in the exemplary embodiments a single mandrel is shown within a tubing string. However, in other embodiments multiple mandrels may be present, axially 35 distributed along the tubing string. In some cases more than one mandrel may require WO 2015/043801 PCT/EP2014/066294 15 remedial attention, such as described above. Where one or more of a number of mandrels remain operational, such operational mandrels may support continued gas lift production, after one or more other mandrels have been sealed. Further, in the exemplary embodiment described the mandrel is a gas lift 5 mandrel. However, embodiments of the present invention may be used in combination with any downhole mandrel, such as a chemical injection mandrel, downhole valve mandrel or the like.

Claims

1. A method for sealing a side pocket of a downhole mandrel in a tubing string, comprising: 5 retrieving a cartridge component from the side pocket of the downhole mandrel; deploying a sealing insert into the side pocket of the downhole mandrel, wherein the sealing insert comprises a swellable sealing element on an outer surface thereof; and swelling the swellable sealing element to provide a seal within the side pocket. 10

2. The method according to claim 1, wherein the sealing element when swollen seals the side pocket of the downhole mandrel to substantially prevent fluid communication outwardly or inwardly of the downhole mandrel via said side pocket. 15

3. The method according to claim 1 or 2, comprising sealing a damaged side pocket of the downhole mandrel.

4. The method according to claim 1, 2 or 3, comprising sealing the side pocket of the downhole mandrel to disable said mandrel. 20

5. The method according to any preceding claim, wherein the downhole mandrel comprises a side port which communicates with the side pocket, wherein the sealing insert provides a seal within the side pocket of the mandrel to seal said side port. 25

6. The method according to claim 5, comprising sealing a side pocket which has become damaged in the region proximate or adjacent to the side port.

7. The method according to claim 5 or 6, wherein the side port of the downhole mandrel is arranged to communicate with an annulus surrounding the downhole 30 mandrel, and wherein the sealing insert provides a seal within the side pocket of the downhole mandrel to substantially prevent fluid communication between the annulus and the downhole mandrel.

8. The method according to claim 5 or 6, wherein the side port of the downhole 35 mandrel is arranged to communicate with a fluid conduit which extends externally of WO 2015/043801 PCT/EP2014/066294 17 the tubing string, wherein the sealing insert provides a seal within the side pocket of the downhole mandrel to substantially prevent fluid communication between the fluid conduit and the downhole mandrel. 5

9. The method according to any one of claims 5 to 8, wherein the sealing insert is deployed into the side pocket such that the sealing element spans the side port.

10. The method according to any preceding claim, wherein the downhole mandrel comprises a gas lift mandrel. 10

11. The method according to claim 10, wherein the cartridge component comprises or a gas lift valve.

12. The method according to any one of claims 1 to 9, wherein the downhole 15 mandrel comprises a chemical injection mandrel.

13. The method according to claim 12, wherein the cartridge component comprises a chemical injection valve. 20

14. The method according to any preceding claim, wherein the sealing insert is of a substantially similar geometrical form as the cartridge component being retrieved.

15. The method according to any preceding claim, comprising retrieving the cartridge component through the tubing string. 25

16. The method according to any preceding claim, comprising retrieving the cartridge component to surface.

17. The method according to any preceding claim, comprising retrieving the 30 cartridge component via a conveyance arrangement.

18. The method according to any preceding claim, comprising deploying the sealing insert through the tubing string. WO 2015/043801 PCT/EP2014/066294 18

19. The method according to any preceding claim, comprising deploying the sealing insert from surface.

20. The method according to any preceding claim, comprising deploying the sealing 5 insert via a conveyance arrangement.

21. The method according to any preceding claim, comprising preventing or restricting flow along the tubing string prior to retrieving the cartridge component. 10

22. The method according to any preceding claim, comprising setting a barrier downhole of the mandrel.

23. The method according to claim 22, comprising setting a barrier within the tubing string downhole of the mandrel. 15

24. The method according to claim 22 or 23, comprising installing a plug within the tubing string.

25. The method according to claim 22, 23 or 24, comprising removing the barrier 20 after the sealing insert has been deployed within the side pocket of the mandrel.

26. The method according to any preceding claim, comprising flowing or placing a fluid into the tubing string. 25

27. The method according to any preceding claim, comprising setting a barrier within an annulus surrounding at least a portion of the tubing string.

28. The method according to any preceding claim, comprising flowing or placing a fluid into the annulus. 30

29. The method according to any preceding claim, comprising exposing the swellable sealing element to a swelling activator including at least one of oil and water.

30. A sealing insert for use in performing the method of any preceding claim. 35 WO 2015/043801 PCT/EP2014/066294 19

31. A sealing insert for use in sealing a side pocket of a downhole mandrel, comprising: a base member; and a swellable sealing element mounted on the outer surface of the base member 5 and configured to swell when exposed to an activator, wherein the sealing insert is geometrically configured to permit insertion within a side pocket of a downhole mandrel such that when the sealing element is swollen said sealing element provides a seal within said side pocket. 10

32. The sealing insert according to claim 31, comprising a connector portion to permit connection to a conveyance arrangement.

33. The sealing insert according to claim 31 or 32, wherein the sealing element is annular. 15

34. The sealing insert according to claim 31, 32 or 33, wherein the sealing element is configured to swell when exposed to a swelling activator including at least one of oil and water. 20

35. The sealing insert according to any one of claims 31 to 34, wherein the base member comprises a cylindrical rod.

36. The sealing insert according to any one of claims 31 to 35, wherein the base member comprises at least one annular recess, wherein the sealing element is 25 received within said annular recess.

37. The sealing element according to claim 35, wherein when the sealing element is in an unswollen state, the sealing element defines an outer diameter which is less than or equal to the outer diameter of the base member. 30

38. A sealed downhole mandrel, comprising: a side pocket including a side port; and a sealing insert sealingly mounted within the side pocket, wherein the sealing insert includes a swollen sealing element which extends at least over the side port of 35 the side pocket. WO 2015/043801 PCT/EP2014/066294 20

39. A method for performing a downhole intervention, comprising: retrieving a cartridge from a side pocket of a downhole mandrel, wherein the retrieved cartridge comprises at least one seal arrangement for providing a seal 5 between the cartridge and the side pocket of the mandrel when located therein; deploying a new cartridge which comprises at least one swellable seal arrangement into the side pocket mandrel of the downhole mandrel; and swelling the at least one swellable seal arrangement to establish a seal between the new cartridge and the side pocket mandrel. 10

40. The method according to claim 39, wherein the new cartridge, once in place, performs substantially the same function as the retrieved cartridge prior to retrieval.

41. The method according to claim 39 or 40, comprising replacing the at least one 15 seal arrangement of the retrieved cartridge with at least one swellable seal element, and then deploying the retrieved cartridge as the new cartridge.

42. The method according to claim 39 or 40, comprising deploying a new cartridge which is different from the retrieved cartridge. 20

43. The method according to any one of claims 39 to 42, wherein the retrieved cartridge comprises at least one non-swelling seal arrangement.

44. The method according to any one of claims 39 to 43, wherein the retrieved 25 cartridge comprises at least one chevron seal arrangement.