Methods and apparatus for use in oil and gas well completion

Abstract

A first aspect of the invention provides a gas or oil well tubing having an annular packer mounted thereon, wherein the annular packer is formed from an eutectic alloy. By prefabricating the annular packer on the tubing it can be placed in situ from the outset and thus can be active by melting at any time to form a eutectic seal quickly and easily. An annular packer with by-pass conduits is also provided to enable cement to be pumped past the annular packer when it is in situ. The annular packer is further provided with conduit clearance means to clear cement from within the conduits.

Claims

1. A gas or oil well tubing having an annular packer mounted on an inner surface thereof, wherein the annular packer is formed from an eutectic based alloy; wherein the packer is configured to define a channel when the tubing and packer are deployed in a well; wherein the channel defines a upper and lower opening; whereby cement can be pumped through the channel; the packer having a volume such that after deployment in a well and pumping of the cement, upon melting and resolidification the packer forms a gas tight seal in the well.

2. The tubing of claim 1, wherein the annular packer comprises with one or more conduits running substantially parallel to the tubing.

3. The tubing of claim 2, wherein the conduits are provided as channels in the inner and/or outer circumferential surface of the annular packer.

4. The tubing of claim 2, wherein the conduits are provided as through holes in the main body of the annular packer.

5. The tubing of claim 1, wherein the tubing is a well casing or well lining.

6. The tubing of claim 1, wherein the tubing and packer are configured to form a liner hanger when deployed in a well, wherein the annular packer configured to form an annular seal with a surrounding tubing; whereby the annular seal is strong enough to provide a weight bearing function, and whereby preferably the annular seal is sufficient to bear the weight of the liner without the need for other forms of retaining means.

7. A method of manufacturing a gas or oil well tubing, said method comprising: providing a length of tubing; mounting a eutectic/bismuth alloy annular packer to the tubing; wherein the packer is configured to define a channel when the tubing and packer are deployed in a well and the packer is engaged against a wall of the well; whereby cement can be pumped through the channel when the packer is engaged against the wall of the well; and forming an annular packer within said tubing by: providing a melted eutectic/bismuth alloy within the tubing and allowing it to cool; and drilling a hole through the alloy along the central axis of the tubing.

8. The method of manufacturing a gas or oil well tubing of claim 7, further comprising providing multiple conduits in the annular packer.

9. The method of manufacturing a gas or oil well tubing of claim 8, wherein the conduits are provided in the form of channels in the inner and outer surface of the annular packer.

10. The method of manufacturing a gas or oil well tubing of claim 8, wherein the conduits are provided in the form of through holes running through the main body of the packer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The various aspects of the present invention will now be described with reference to the drawings, wherein:

(2) FIG. 1 is a diagrammatic representation of the key stages of the deployment and operation of the oil/gas well tubing of an embodiment of the first aspect of the present invention;

(3) FIG. 1a is a diagrammatic representation of an alternative deployment of the tubing of the first aspect;

(4) FIG. 1b is a diagrammatic representation of a second alternative deployment of the tubing of the first aspect;

(5) FIG. 2 shows a perspective view of an embodiment of the first aspect of the present invention;

(6) FIG. 3 shows an end view of one variant of the embodiment shown in

(7) FIG. 2;

(8) FIG. 4 shows an end view of a second variant of the embodiment shown in FIG. 2;

(9) FIG. 5 shows a diagrammatic representation of the key stages of the deployment of a liner hanger in accordance with an embodiment of the second aspect of the present invention;

(10) FIG. 5a shows a diagrammatic representation of the key stages of the deployment of an alternate embodiment of the second aspect of the present invention;

(11) FIG. 6 shows a perspective view of an embodiment of the third aspect of the present invention;

(12) FIG. 7 shows a diagrammatic representation of the key stages of the deployment and operation of the casing drilling variant of the third aspect of the present invention;

(13) FIG. 8 shows a diagrammatic cross-sectional representation of an alternative embodiment of the first aspect of the present invention;

(14) FIG. 9 shows an end view of one variant of the embodiment shown in FIG. 8;

(15) FIG. 10 shows an end view of a second variant of the embodiment shown in FIG. 8;

(16) FIG. 11 shows a preferred embodiment of a stackable variant of the annular packer of the present invention;

(17) FIG. 12 shows a middle section of the annular packer with a preferred arrangement of conduit clearance means mounted on thereon;

(18) FIG. 13 shows an end section of the annular packer with a preferred arrangement of rubber seals mounted thereon;

(19) FIG. 14 shows a diagrammatic representation of the interaction between a rubber seal of the annular packer and an adjacent surface;

(20) FIG. 15 shows the operational stages of the deployment of a preferred embodiment of the annular packer of the present invention;

(21) FIG. 16 shows a diagrammatic cross-sectional representation of an embodiment of the collar joint provided by the fourth aspect of the present invention;

(22) FIG. 17 shows a diagrammatic cross-sectional representation of the embodiment of FIG. 16 being heated to cause the alloy to flow into the join between the tubing and the collar joint.

DETAILED DESCRIPTION OF THE VARIOUS ASPECTS OF THE PRESENT INVENTION

(23) The various aspects will now be described with reference to the Figures, which provide a collection of diagrammatic representations of embodiments of the each aspect of the present invention to aid the explanation of their key features.

(24) One of the central features of a number of the aspects of the present invention is formation of prefabricated oil/gas tubing with a eutectic or other bismuth alloy annular packer mounted to the said tubing. Although the term annular packer is used throughout it is appreciated that the term thermally deformable annulus packer is also an appropriate description given the alloy aspect of the described annular packers. The terms can therefore be used interchangeably.

(25) The term prefabricated is intended to cover situations where the annular packer is mounted on the tubing either in a factory or on site, but always before the tubing is deployed down a well bore. This is clearly distinct from existing uses of eutectic and other bismuth based alloys as a sealant, wherein the alloy is deployed separately from the tubing at a later stage—which is usually after completion of the well.

(26) It will be appreciated that, unless otherwise specified, the materials used to manufacture the components of the various apparatus described hereinafter will be of a conventional nature in the field of oil/gas well production.

(27) Turning now to the embodiment of the first aspect of the present invention shown in FIGS. 1-4, and in particular FIG. 2 initially. FIG. 2 shows an oil/gas well tubing 1 of the present invention in the form of a length/section of production pipe 2 with an alloy annular packer 3 mounted on the outside thereof.

(28) Although not shown in the Figures it is envisioned that the externally mounted annular packer might preferably be formed from multiple component parts that combine to surround the length of production pipe 2 so that the process of mounting (and possibly remounting) the annular packer is made easier.

(29) As will be appreciated from FIG. 1 the diameter of the annular packer 3 is sufficient to provide a close fit with the outer wall of the well 5, which may be provided by a rock formation 4 or as appropriate a well casing or lining.

(30) In order to explain the benefits of the tubing 1 reference is made to FIG. 1, which shows three key stages in the working life of the tubing 1. In the first stage the tubing 1, which comprises the section of production tubing 2 with the annular packer 3 mounted on the outer surface, is attached to tubing 6 and delivered down the well bore 5 that has been created in the underground formation 4 using conventional means.

(31) It is appreciated that tubing 1 and 6 are typically connected together above ground and then deployed down the well. However in order to clearly illustrate that tubing 1 and 6 are initially distinct they are initially shown in FIG. 1 as being separate.

(32) In the shown example the tubing 1 is attached to the top of the tubing 6. It is envisioned that advantageously the tubing 1 of the present invention may be connected to existing production tubing 6 using the collar joint of the present invention shown in FIGS. 16 and 17, although this is not considered essential. It is appreciated that alternative approaches to deploying a series of sections of well tubing can be employed in concert with the present invention.

(33) Once the production pipework, which comprises tubing 1 and 6, has been deployed within the well 5 cement 7 can be poured or pumped into the annular space between the formation 4 and the pipework (or, if appropriate, between a well casing/lining and the pipework). Once set the cement 7 will seal the well 5 so that the only access to the oil/gas deposit is via the production tubing 1,6.

(34) In the event that a crack or gap develops in the cement seal and forms a leak a heater 8 can be deployed down the well using a wire line 9 or coil tubing, for example, to a target region inside the tubing 1 that is proximate to the alloy annular packer 3. Once in place the heater 9 can be activated to melt the alloy 3, which causes it to turn into a liquid and flow into the cracks/gaps in the cement plug 7.

(35) When the alloy 3 of the annular packer, which may be a eutectic alloy or other forms of bismuth alloy, cools it expands and plugs the cracks/gaps and reseals the cement plug 7 and stops the leak.

(36) It is appreciated that various annular spaces are created during the formation of a well and it is envisioned that the present invention can therefore be usefully employed in variety of different arrangements without departing from the scope of the present invention.

(37) In the described embodiment the cement is poured (or pumped) into the annular space after the tubing 1, with its annular packer 3, has been deployed within the well.

(38) In arrangements where the diameter of the annular packer 3 is close to the internal diameter of the rock formation 4 (or well casing/lining—not shown) it is considered advantageous to provide the annular packer 3 with conduits to facilitate the passage of cement through and around the annular packer 3 so that it can reach the lower regions of the well 5.

(39) It is envisioned that rather than being deployed above the level of the cement the tubing 1 may also be completely surrounded by and embedded within the cement 7. FIGS. 1a and 1b show such arrangements.

(40) The embodiment of the tubing shown in FIG. 1a has an annular packer 3 of a reduced diameter that does not extend all the way to the outer formation (or casing). In is envisioned that such embodiment is suitable for sealing micro annuli leaks; such as those formed by constant expansion and contraction of the production tubing (see above).

(41) The embodiment shown in FIG. 1b has an annular packer 3 with a diameter that extends to the surrounding formation (or casing). It is envisioned that this embodiment is more suitable for repairing cracks that extend across the entire cement seal.

(42) FIG. 3 shows a first variant of the annular packer 3, which is provided with a plurality of through holes 10. The through holes 10 are arranged to permit the passage of wet cement through the main body of the annular packer 3.

(43) FIG. 4 shows a second variant of the annular packer 3, which is provided with a plurality of channels 11 in the outer surface of the annular packer 3.

(44) One specific application of the annular packer of the present invention is in the formation of liner hangers. It is envisaged that the alloy annular packer can be used to form an annular seal between a liner and a surrounding surface, such as a well casing or possibly even the surrounding formation. By using an annular packer to form an annular seal located towards the top section (i.e. the section of the liner closest to the ground surface) of the liner the liner can effectively be hung within a well hole.

(45) Turning now to FIG. 5, in which is shown the key stages of deploying a liner hanger in accordance with the present invention within a well hole. It will be appreciated that the outer well casing 12 is essentially the same as the tubing shown in FIG. 8, in that it comprises a length/section of tubing 12 with an annular packer 14 mounted on the outside thereof.

(46) In use the well casing 12 is deployed within a well hole. The well casing 12 is secured in place within the well hole using standard means, although it is envisaged that alloy annular packer might also be used for this purpose.

(47) Although not shown it is envisaged that the well casing (or well liner) may be provided with a skirt or ‘cool area’ to slow the flow of the melted alloy so that it is not lost down the well but instead cools in the target region. Further details of suitable skirting can be found in International PCT Application No. WO2011/151271. It is appreciated that the well fluids will act to quickly cool the heated alloy ensuring that it is not is a flowing state for very long.

(48) Although not shown, it is envisaged that the skirt may further comprise a swellable or intumescent material that is caused to expand when exposed to heat. This further enhances the ability of the skirt to check the flow of the molten alloy so that it can cool in the target region.

(49) Once the well casing 12 is secured in place within the well a well lining or liner 13 is delivered down the well. The well lining/liner 13 has a diameter that is small enough to enable it to pass inside both the well casing 13 and the annular packer 14.

(50) Once the well lining/liner is located at its required position within the well (i.e. so that the majority of the liner extends down the well away from the annular packer) a heater 15 is deployed, via a cable line 16 (or suitable alternative such as drill pipes), down the well hole and into the well lining/liner 13. The heater 15 is deployed to a target region in which the well casing, the annular packer 14 and the well lining/liner 13 are all aligned.

(51) Once in position the heater, which is preferably a chemical based heated source, is activated and the alloy of the annular packer 14 is melted causing it to sag. After a period of heating that is calculated to adequately melt the alloy the heating stops (and the heater removed) and the alloy is allowed to cool and resolidify. As the alloy resolidifies it forms an annular seal 14a between the out well casing 12 and the inner well lining/liner 13.

(52) FIG. 5a shows an alternative arrangement of the liner hanger deployment shown in FIG. 5. Although the components involved are the same, rather than mounting the annular packer to the well casing 12, the annular packer 14 is mounted on the outside of the well lining/liner 13. In this alternative arrangement the well lining/liner 13 is essentially the same as the tubing shown in FIGS. 1-4.

(53) The third aspect of the present invention is applicable in casing drilling operations, which are typically employed when drilling into soft or loose formations (e.g. sand, mud, etc. . . . ).

(54) FIG. 6 shows an embodiment according to the third aspect of the present invention. The drilling casing 20 comprises a section of tubing in the form of a well casing 21. An annular packer 22 is mounted in the outer surface of the casing 21. On the leading end of the casing is provided a drill head 23. In use the entire drilling casing 20 is rotated to effect a drilling action on a formation that is comprised of loose material.

(55) It is envisioned that the dimensions of the drilling casing components shown in FIG. 6 are not limiting and the arrangement is primarily provided to demonstrate the principle of operation of the third aspect of the present invention. For instance it is envisaged that the diameter of the drilling head 23 would in practise be closer to that of the annular packer so that the well bore being formed can accommodate the passage of the annular packer 22 as the drilling casing 20 carries out the drilling operation.

(56) The operation of the drilling casing 20 will be better appreciated upon consideration of FIG. 7, which show the key stages of a drilling action. The first stage shown in FIG. 7 represents the standard drilling operation wherein the drilling casing 20 is rotated about its central axis so as to create a well bore 25 in the formation 24. Drilling fluid 26 is provided within the well bore 25 (possibly via the casing 20) to assist the drilling process (i.e. cool the drilling tool and facilitate removal of swarf/drilling waste from the drill face).

(57) The first stage of FIG. 7 shows a cavity 27 in the drilling path of the well bore. In the second stage of FIG. 7 the drilling action has exposed the cavity 27 and in doing so has allowed the drilling fluid 26 to leak away. If left unchecked the loss of the drilling fluid would severely impair the drilling process and could damage the drilling tool 23.

(58) In order to remedy this situation it would normally be necessary to stop the drilling and remove the drilling casing so that a suitable sealing material (such as cement) can be deployed to plug or cap off the cavity. This operation is time consuming and thus, as a result of lost oil production, extremely costly.

(59) As will be appreciated from the third stage shown in FIG. 7, the drilling casing 20 of the present invention provides a much quicker solution because the eutectic or indeed other bismuth based alloy—which is capable of providing an effective plug—is already present in the locale of the cavity. It is therefore simply a case of heating the eutectic/bismuth based alloy 22 so that it melts, flows into the cavity and cools, thereby plugging (or capping off) the cavity.

(60) In FIG. 7, for the sake of aiding understanding, the heating means is shown as a separate heating tool that is deployed down the well, via the inside of the casing 21, until it reaches the target region adjacent the annular packer 22. It is envisaged that an alternative heat source, preferably in the form of a chemical heat source, might be provided on the drilling casing 20 before it is deployed. This could be activated from the surface or remotely (e.g. using a pressure pulse, radio wave, etc. . . . ).

(61) The majority of the embodiments described so far have involved the annular packer being mounted on the outer surface of suitable tubing, whether in the form of a section of production tubing, well casing/lining, adaptor tubing or a drilling casing.

(62) However it is envisioned that the annular packer might also be mounted on the inner surface of suitable tubing without departing from the scope of the present invention. It is appreciated that suitable tubing may include sections of well casing and well lining.

(63) In this regard reference is now made to FIG. 8, which shows an embodiment of the tubing 30 of first aspect of the present invention wherein the annular packer 32 is mounted within the section of well casing 31 on an inner surface thereof.

(64) Once again, as with FIGS. 3 and 4, two variants of the tubing 30 are shown end on in FIGS. 9 and 10. Specifically FIG. 9 shows the variant of the annular packer 32 with cement by-pass conduits in the form of through holes 33, whereas FIG. 10 shows a variant of the annular packer 32 is provided with channels 34 in the inner circumferential surface.

(65) FIG. 11 show three views (a combined, an exploded, and a cross-sectional) of a preferred stackable arrangement of the annular packer 80. The annular packer is shown without a well casing/tubing as such is not essential to the provision of an operational annular packer.

(66) As will be best appreciated from the exploded view, in the example shown the packer 80 is formed from two end sections 81 and two middle sections 82 all of which are joined together with connection means 83. Although not shown in detail it will be appreciated that that the connection means may be in the form of pairs of nuts and bolts located around the perimeter of the annular packer.

(67) Although the shown example only has four sections it is envisaged that the number of middle sections can be reduced or increased to vary the length of the annular packer, thus making this embodiment much more flexible for a range of repair jobs.

(68) On the outside of each section is provided at least one conduit clearance means 85, which essentially comprise a metal spring ring that has been stretched fit around the annular packer 80. Each spring ring is retained within a recess 91 (see FIG. 12). The spring ring may preferably be made from steel as this is a relatively cheap material. However, in cases where higher temperature tolerances are required it is envisioned that alternative metals and alloys may be employed to form the spring ring.

(69) In stretching the spring ring 85 the conduit clearance means is forced out of its preferred state. The desire of the spring ring to return to its original diameter serves to resiliently bias the conduit clearance means towards the annular packer and the conduits (not shown) that run along its length through the middle of each packer section. Further details of the operation of the conduit clearance means are provided below.

(70) In addition to the conduit clearance means 85, the end packer sections 81 are provided with one or more rubber seals 84. These seals facilitate the formation of a seal between the annular packer 80 and the tubing into which the packer is inserted. In the shown example two rubber seals are provided on each end section so as to allow for one of the seals to fail. This is important because the seals can become damaged during the deployment of the annular packer within an outer tubing structure. In view of this it is envisaged that more than two rubber seals may be provided on each section to provide additional redundancy.

(71) Turning now to the cross-sectional view of the stackable annular packer 80 it will be seen that further seals 86 and conduit clearance means 87 are provided on the inner surface of the annular packer 80.

(72) The seals 86, which are only provided on the end sections 81, are similar in nature to the externally mounted seals 84.

(73) The inner conduit clearance means 87 are once again provided by spring rings. However in contrast to the outer means 85 the inner spring rings are squeezed into the inner space of the annular packer.

(74) In squeezing the spring ring 87 the conduit clearance means is forced out of its preferred state. As with the outer means 85, the desire of the spring ring to return to its original diameter serves to resiliently bias the conduit clearance means towards the annular packer and the conduit (not shown) that runs along its length through the middle of each packer section.

(75) The arrangement of the conduit clearance means 85 and 87 will be better understood from the enlarged cross-sectional view of annular packer section 82 shown in FIG. 12.

(76) The section 82, and indeed each of the annular packer sections, is essentially formed from an alloy 88. Each section is preferably formed by casting the alloy 88 in to the required shape of the annular packer section 82. However, it is also envisioned that the end sections might alternatively be formed from a metal, such as aluminium, to provide additional structural strength to the packer.

(77) The alloy 88 is cast with one or more recesses 91, 92 on its inner and outer surface to receive the above described conduit clearance means 85, 87. The section of eutectic alloy annular packer is also provided with a void 90 into which tubing may be received.

(78) In the shown example the alloy 88 of the packer section 82, and indeed the entire packer 80, is provided with a plurality of conduits 89. As already explained the purpose of each conduit 89 is to permit the flow of fluid, and in particular cement, through the annular packer during the completion of a well or setting of a plug, for instance.

(79) The conduit 89 is defined by the eutectic alloy 88. However once cement has been allowed to flow through the conduit 89, as when cement is being pumped down hole past the annular packer via one or more conduits 89, some cement can remain in the conduit and set there.

(80) The presence of a cement rod formed within each conduit is considered undesirable as it would prevent the alloy from forming a complete alloy plug across the entire annular space (i.e. between the inner tubing, such as a production tubing, and an outer tubing, such as well casing). In view of this it is desirable to break up the cement rod so that an unbroken eutectic plug can form. This is the role of the conduit clearance means 85, 87.

(81) Before the alloy 88 of the annular packer 80 is melted the conduit clearance means 85, 87 are held in abeyance by the body of the alloy. However once the alloy begins to melt and flow the conduit clearance means 85, 87 are no longer held and they are able to ‘spring back’ to their preferred shape.

(82) This results in the outer conduit clearance means springing inwards towards the conduits and the inner conduit clearance means springing outwards towards the conduits. In both cases this results in any cement that may have accumulated in the conduit being subjected to a smashing force, thereby breaking up the cement. Breaking up the cement allows for melted alloy the form an unbroken plug across the entire annular space.

(83) Turning now to FIGS. 13 and 14, which show enlarged cross-sectional views of the end packer section 81, the operation of the rubber seals 84 will be considered in more detail. The end section 81 is provided with a pair of seals 84 on the outer surface of the end section and on the inner surface of the end section.

(84) The seals are provided within recesses located towards the leading edge of the end section 81 to isolate the main body of the eutectic alloy 88 from any cement that is pumped into the well hole. Preferably the pairs of seals are provided on both the inner surface and the outer surface so as to allow for potential failure of one of the seals during the deployment of the annular packer 80. It is envisaged that more or less seals might be employed as required without departing from the present invention.

(85) In order to aid the description of the seal 84 FIG. 14 is provided to show a further enlarged cross-sectional view of a seal when the packer is inserted within a tubing 93. As will be appreciated from FIG. 14 the seal 84 makes contact with the tubing 93 and in doing so forms a seal.

(86) The seal 84 is provided with at least one aperture 94 so that the seal can be self-energising. When the seal is subjected to high pressure (e.g. fluid pressure) from below the seal (as might occur in a typical installation) the aperture 94 allows the fluid to pass into the inner space 95 of the seal 84. The flow of the high pressure fluid into the inner space 95 serves to further push the seal towards the tubing 93, thereby energising the seal and increasing its sealing properties.

(87) Although not shown in detail it is envisaged that similar seals arrangements can be provided on the inner surface of the packer section 81.

(88) The deployment of an annular packer 80 of the present invention will now be described with reference to FIG. 15, which shows some (although not necessarily all) of the stages of the deployment process.

(89) The annular packer 80 is inserted into a well casing/tubing 110 that is located within a well bore in a rock formation 100. The annular packer 80 is mounted on an inner tube 97.

(90) One or more centralisers 96 are provided at the ends of the annular packer 80 to ensure it remains centralised as it is deployed down the well casing/tubing 110. This is desirable as it ensures that the distance between the inner tube (upon which the annular packer is mounted) 97 and the outer well casing/tubing 110 is substantially the same all around the circumference. This in turn aids the formation of a reliable eutectic plug.

(91) Once the annular packer 80 is in position cement 120 is pumped down the well hole via the annular space provided between the inner 97 and outer well 110 tubing. When the cement reaches the annular packer 80 it enters the multiple conduits 89 that are provided therein and flows through the packer to reach the annular space below the packer.

(92) The cement is then allowed to set and form the cement plug between the inner 97 and outer 110 tubes. The annular space above the annular packer may or may not be filled with cement 120 depending on the operational requirements of the well.

(93) At any time after the cement 120 has set a heater can be deployed down the well hole to region of the annular packer 80. This is the third stage shown in FIG. 15. The heater 130, which is deployed using standard delivery equipment such as a wire line 131, then heats the annular packer 80 and melts the alloy so that a plug can be formed in the normal way.

(94) It will be appreciated that the conduits 89 are filled with cement 120. The presence of solid cement path within the body of the alloy is undesirable because such might provide a potential leakage point within any alloy plug formed. In view of this it is important that the cement paths formed within the conduits are broken up. This function is carried out by the conduit clearance means 85, 87.

(95) As will be appreciated from the above description of the conduit clearance means 85, 87, once the alloy 88 of the packer 80 has begun to melt the spring rings are no longer held in position and can spring back towards the conduits. This action imparts a breaking force on the cement rods and smashes them in to smaller non-continuous pieces.

(96) The smaller non-continuous pieces allow the melted alloy to flow and form a continuous uninterrupted alloy plug across the entire annular space between the inner tubing 97 and the outer casing/tubing 110.

(97) Although the above described application of the annular packer relates to the completion of an oil/gas well it is appreciated that the functionality of the packer of the present invention extends to other applications.

(98) For example, the packer can be placed in the annulus during the completion of the well but not melted. Then, when the well comes to the end of its useful life, the annular packer can be melted in the annulus to form a gas tight seal against which a well bore plug can be set. It is envisaged that this would help the company comply with forming a gas tight seal from rock to rock.

(99) Another example of an alternative application is the deployment of the annular packer between producing zones in open hole gravel pack (OHGP). In this way if one zone is watered out the annular packer can be melted to seal off the gravel pack for that zone.

(100) FIGS. 16 and 17 provide cross-sectional views of an embodiment of a collar joint 40 according to a fourth aspect of the present invention. The collar joint is provided with a first tubing engagement means 41a and a second tubing engagement means 41b, both in the form of inwardly facing screw threads. As will be appreciated from FIG. 17 in particular the screw thread 41a and 41b engage with complementary screw threads 46 and 46a on tubing sections 45 and 45a.

(101) Although the screw threads of the collar joint are shown as facing inwards it is envisioned that the screw orientation of the screw threads on the collar and the tubing could be reversed without departing from the present invention (i.e. the screw threads on the tubing could face inwards and the threads on the collar could face outwards).

(102) In the embodiment being described the collar joint is provided with two separate rings 42 and 43 or eutectic/bismuth alloy, one for each screw thread. The upper alloy ring 42 is located in a recess (shown as 47 in FIG. 12) located above the upper screw thread 41a of the collar joint 40. The lower alloy ring 43 is located in a recess (shown as 48 in FIG. 12) above the lower screw thread 41b.

(103) When the tubing 45, 45a is screwed into the collar joint 40 the recessing of the alloy rings ensures that they do not create an obstruction.

(104) In the event that the joint between the adjacent sections of tubing 45, 45a develops a leak heater 49 is deployed via the tubing 45 to a point that is adjacent the collar joint 40 via a standard delivery means 50 (e.g. wire line). Once in place the heater 49 can be operated to heat the alloy rings, which can then flow under gravity into the screw threaded joint located below the respective recesses 47, 48. The alloy is then allowed to cool and expand within screw threaded region to enhance the seal formed.

(105) Although the alloy rings are intended for use only when a leak develops at a joint it is also envisaged that the alloy may be deployed even when there is not leak with the sole purpose of providing an enhanced seal at a joint section.