WO2017041832A1

WO2017041832A1 - Improvements in methods and apparatus for connecting tubes

Info

Publication number: WO2017041832A1
Application number: PCT/EP2015/070508
Authority: WO
Inventors: Christopher James BOWLES
Original assignee: Bowles Christopher James
Priority date: 2015-09-08
Filing date: 2015-09-08
Publication date: 2017-03-16

Abstract

A method of connecting a tube to a further tubular element, including the steps of interposing a sealing ring between the end faces of the tube and the further tubular element; applying an axial compressive force to the assembly to compress the sealing ring to form a seal between the tube and the tubular element and connecting the tube to the tubular element by means of a connector, attached by a dimple arrangement to maintain the compressive force sufficiently to maintain the seal. Also provided is apparatus for making such a connection having a top sub-assembly with a plurality of threaded holes passing through its wall to allow grub screws to be inserted to engage with the outside of a tube within the top sub-assembly; a thread at one end for connection to a bottom sub-assembly; a bottom sub-assembly with a thread at one end for connection to the top sub-assembly, a tool connector at the other end, and a cavity to accommodate a seal ring housing. A seal ring housing is also provided having an abutment face for a sealing ring.

Description

Improvements in Methods and Apparatus for Connecting Tubes

Field of the Invention

The invention relates to a connection assembly for connecting tubes to other tubular elements such as tool connectors or other tubes, especially for use in the drilling industry, for example in the oil and gas industry. More particularly, the invention relates to the use of dimple connections and sealing arrangements on such connectors. The invention also relates to methods for joining a tube to other such tubular elements.

Background to the Invention

In the drilling industry, and in particular for oil and gas, underground operations are often carried out by affixing tools and the like to the end of tubes, through which material can flow. The tubes used are often so-called "coil tubing" usually made of steel, and that are stored as a coil of material that can be uncoiled for use. In order to attach such tools to the end of the tube, a connector is required. Two forms of connector are common: those that connect to the inside diameter of the tube (Inline Connectors) and those that connect to the outside diameter of the tube (Outline Connectors). Inline connectors have the advantage that there is no increase in the outside diameter of the coil tubing by use of the connector, but with the disadvantage that the bore is restricted, leading to a smaller flow through the tube once the connector is in place. Outline connectors have the advantage that they do not restrict the bore of the tube following connection, although the increased outside diameter of the assembly can restrict their use in some circumstances. The present invention relates to improved methods and apparatus for forming such connections. External and internal connectors are fixed on to the outside diameter and inside bore of the coil tubing at the end of the coil tubing reel and are used to attach and run (deploy) what is known in the industry as a Bottom Hole Assembly (BHA), which is a screwed-together combination of pressure-operated tools, such as: jarring subs, hammers, back pressure valves, and milling bits, (called a tool string). This is used to carry out live oil or gas well intervention work, e.g.

descaling, fishing out of well trapped/broken equipment, and milling/drilling operations.

Existing coil tubing internal and external connectors typically consist of three types, Grapple type, Grub-screw type and Internal Dimple type connectors.

The installation method varies between types of connector. Grapple type involves sliding the connector's threaded compression nut/cap and the (surface hardened) tapered grapple spiral teeth slip over and up the tubing, followed by the bottom sub containing the Ό'-ring seals, which is tapped on to the end of the tubing until it passes the Ό'-ring seal area and bottoms out inside the housing. The compression nut/cap is then slid down the tube over the grapple spiral teeth slip and is joined on to the bottom sub housing thread by manually tightening down the threaded compression nut/cap with a spanner or wrench while simultaneously holding the bottom sub housing from rotating by using a second spanner or wrench. This compresses, via the taper, the grapple teeth slip on to the outside of the coil tubing to form the grip. Grub- screw type installation involves cold forming indentations in the coil tubing using an existing manual dimple indentation tool. After the indentation tool is removed a Grub-screw connector is then aligned over the cold formed dimples, and grub-screws are screwed into the indentations, to secure the connector in place. Internal Dimple type connectors installation involves cold forming indentations in to the coil tubing and directly into the already inserted and aligned internal dimple connector using manual or hydraulic installation tool, to secure the connector in place.

There are three fundamental areas that determine the success and reliability of current Grapple type, Grub-screw type and Internal Dimple type connector design: 1 : The grapple slip spiral teeth bites in to the coil tubing to provide tensile and torsion capabilities and prevent the grapple from being pulled from the tube or being rotated in the same direction as the spiral (necessary for rotating tools milling/drilling tools - these all typically rotate clockwise). The Grub-screw type connector uses grub screws, which are tightened in to the cold formed

indentations on the coil tubing to achieve similar tensile and torsion capabilities of the Grapple type connector. The Internal Dimple type connector after inserting into the coil tubing uses cold formed indentations in to the coil tubing, which are formed through into the dimples of the Internal Dimple type connector to achieve similar tensile and torsion capabilities of both the Grapple and Grub-screw type connectors.

2: The two o-ring elastomer seal arrangement housed inside the grapple connector's bottom sub housing or the grub-screw connector's housing, or on the internal dimple connector - are essential for a pressure-tight seal to prevent pressure drop when pumping the necessary fluids through the coil tubing to operate the BHA when carrying out operations.

3: The installation procedure for the connectors to ensure the tensile and torsion capabilities meet operational requirements and a pressure tight seal is achieved.

Existing Coil Tubing Grapple Connectors, Grub-screw connectors, and Internal Dimple connectors, are prone to operational problems because of inconsistency with the installation process, which can lead to the connector slipping on the tubing and/or strangulation and collapse of the tube resulting in reduced sealing capability. Once installed, these connectors are expected to withstand upward and downward jarring (hammer action) with accelerated impacts of several 100,000 lbs force and torsional forces of around 5,000 ft/lbs (dependent on tubing strength) during fishing /trapped in hole operations, with single straight pull loads at surface equivalent to 80% of tubing yield.

Existing external coil tubing grapple connectors and Grub- screw connectors, and Internal Dimple connectors generally use two elastomer seals (Ό'-rings) when installed to seal against the outside of the coil tubing and can be prone to sealing failure while under pressure causing fluid leaks and, notably, loss of operating pressure (typical internal coil tubing pressure 5,000psi). The current problems with existing designs have been around for many years and are now inherent with grapple, grub-screw, and internal connector use. For example, there are several different brands of grapple connectors, grub-screw, and internal connectors all with varying join-up threads and different tapered grapple slips rendering the installation of each connector unique to its own brand, i.e. the amount of turns required to set the grapple on the tube, the position of the o-ring seals and, ultimately, the effectiveness of o-ring seals in this application after considering standard coil tubing is produced with surface finish and tolerances that do not have to comply with British Standard o-ring sealing specifications (BS

1806: 1989). In addition, the tubing suffers ovality, nicks and abrasions, and other surface damage during its production and during operations being reeled on and off the coil tubing drum rendering the tubing surface in many instances unsuitable for a pressure retaining o-ring seal.

It is amongst the objects of the present invention to attempt a solution to these problems.

Summary of the Invention

Accordingly, the invention provides a method of connecting a tube to a tubular element, said method comprising the steps of: abutting an end face of the tube to a first face of a sealing ring; abutting an end face of the tubular element to a second, opposite, face of said sealing ring; applying an axial compressive force to urge the tube towards the tubular element, thereby compressing said sealing ring to form a seal between the tube and the tubular element; connecting said tube to said tubular element by means of a connector to maintain said compressive force sufficiently to maintain the seal so formed; wherein said connector is attached to said tube by means of a dimple arrangement.

In preferred embodiments of the invention, said tubular element comprises a second tube. In alternative preferred embodiments, said tubular element comprises a downhole tool connector. In any embodiment of the invention it is preferred that said dimple arrangement is created by: forming indentations on an outside surface of said tube; locating said connector around the outside of the tube; and attaching the connector to the tube by means of grub screws that engage with said indentations.

It is also preferred that in any embodiment of the invention where grub screws are not employed, said dimple arrangement is created by: providing a connector with indentations on its outside surface; locating said connector within the bore of the tube; and applying point loads to the tube at points corresponding to said indentations, thereby causing the tube wall to engage with said indentations.

The invention also provides apparatus for use in a method described herein, said apparatus comprising: (a) a top sub-assembly having an aperture therethrough to allow it to be passed over a tube to be connected, a plurality of threaded holes passing through the wall of the top sub-assembly to allow grub screws to be inserted to engage with the outside of a tube within the top sub-assembly, and a thread at one end for connection to a bottom sub-assembly; (b) a bottom subassembly comprising a thread at one end for connection to said top sub-assembly, a tool connector at the other end, and a cavity to accommodate a seal ring housing; (c) a seal ring housing having an aperture therethrough to accommodate the end of a tube to be connected; and a step within the bore of the housing to form an abutment face for a sealing ring. Preferably, said seal ring housing has a tapered portion on its external surface; said bottom sub-assembly cavity has a correspondingly tapered configuration; and an Ό'-ring groove is provided on the external surface of said seal ring housing or the internal surface of said cavity to allow an Ό'-ring seal to be formed between them.

The scope of the invention also includes a method of connecting a tube to a tubular element substantially as described herein, with reference to and as illustrated by any appropriate combination of the accompanying drawings.

The scope of the invention also further includes apparatus for use in a method of connecting a tube to a tubular element substantially as described herein, with reference to and as illustrated by any appropriate combination of the

accompanying drawings.

Brief Description of the Drawings

The invention will be described with reference to the accompanying drawings, in which:

Figure 1 illustrates, in cross-sectional view, a top sub-assembly for use in a method of the invention;

Figure 2 illustrates, in cross-sectional view, a top sub-assembly and an end of a length of tubing as part of a method of the invention;

Figure 3 illustrates, in cross-sectional view, a seal ring housing and seal for use in a method of the invention;

Figure 4 illustrates, in cross-sectional view, a bottom sub-assembly, seal ring housing and seal for use in a method of the invention;

Figures 5 and 6 illustrate, in cross-sectional view, stages in a method of the invention;

Figure 7 illustrates a jig, in use, as part of a method of the invention;

Figure 8 illustrates the use of a dimple and grub screw arrangement as part of the method of the invention;

Figures 9-10 illustrate how the method of the invention may be used to form an inline connection;

Figures 11-12 illustrate a preferred configuration of a sealing ring abutment; Figures 13-14 illustrate how the method of the invention may be used to form an inline connection; Figures 15-16 illustrate a preferred sealing ring for use in the invention;

Figures 17 and 18 illustrate a preferred arrangement of locking a sealing ring into position; and

Figures 19 -20 illustrate an assembly jig and method of forming an inline connection.

Detailed Description of the Invention

Figure 1 illustrates, in partial cross-sectional view an embodiment of a top sub- assembly, generally indicated by 1, forming an element of apparatus of the invention and illustrating (in combination with the following figures) an embodiment of a method of the invention. The top sub-assembly is generally tubular in configuration, having a bore 2 therethrough, sized to accommodate a tube to be connected. Towards a first (uphole) end 3 of the sub-assembly are provided a number of threaded holes 4 passing through the wall 5 of the subassembly. The holes 4 are disposed around the circumference of the subassembly, as indicated by the positions marked 4'. On the external surface of the sub-assembly 1, and at the other (downhole) end 6 of the assembly is an external thread 7 to enable the top top-assembly to be connected to a bottom sub-assembly to be described below. This second end 6 is also provided with a section having an increased bore 8 to accommodate the end of a seal ring housing, to be described below.

Figure 2 illustrates, in cross-sectional view, the top sub-assembly 1 of Figure 1 into the bore 2 of which has been inserted the end of a length of tubing 9. The outside surface 10 of the tubing 9 has been provided with a series of indentations 11 that correspond to the position of the holes 4 in the top sub-assembly 1. Grub screws 12 are inserted into the threaded holes 4 to engage with the indentations 11 on the surface of the tubing 9 to connect the tubing to the top sub-assembly 1. The end of the tubing 13 extends beyond the end of the top sub-assembly 1. Figure 3 illustrates, in cross-sectional view, a seal ring housing, generally indicated by 14, and a sealing ring 15 for use in the method of the invention. The seal ring housing 14 is generally tubular in form, having a bore 16 to accommodate the end of a tube to be connected. The bore 16 is provided with an inwardly-extending step 17 around the internal circumference of the bore to provide an abutment surface for the sealing ring 15. An external portion of the seal ring housing is provided with a tapered region 18 and a Ό'-ring groove 19 into which an Ό'-ring (not illustrated) may be located to provide a seal between the seal ring housing 14 and a bottom sub-assembly to be described below. The sealing ring 15 is of generally annular configuration. Suitable materials for such a sealing ring would include graphite, soft iron, copper, Stainless steel, nickel- chromium alloys such as those sold under the Registered Trade Mark "Inconel", metal (generally), hollow rings, and gas filled rings. Particularly preferred embodiments of seal arrangements are described below. Such a seal arrangement might also comprise a modification of said abutment face, for example by provision of a more malleable portion of an abutment face by incorporating a ring of softer material into the abutment face.

It is preferred that the sealing ring 15 is formed of metal, and more preferably hollow. For metal rings, copper (and especially annealed copper) is preferred, or for situations where hydrogen sulphide is present, malleable cast iron. The sealing ring may, in preferred variants, be hollow, and filled with a filler such as asbestos or an inert gas.

Figure 4 illustrates, in cross-sectional view, a bottom sub-assembly used in a method of the invention, and generally indicated by 20. The bottom sub-assembly 20 is again of generally tubular form, and is provided at one end with an internal thread 21 to allow it to be attached to the top sub-assembly 1 via its external thread 7. The other end of the bottom sub-assembly is provided with a tool connector region 22, in this embodiment comprising a second external thread 23 and an external Ό'-ring arrangement 24. The interior of the bottom sub-assembly is provided with a cavity 25 so sized and shaped as to accept a seal ring housing 14. The inside of the cavity is provided with a tapered region 26 to match the tapered region 18 on the seal ring housing 14.

Figure 5 illustrates, again in cross-sectional view, a further stage in the method of attaching the tube 9 to the tubular element, said element in this instance comprising the bottom sub-assembly 20 with tool connector 22. The top sub- assembly 1 and the bottom sub-assembly have been joined together by means of the threaded regions 7 and 21 thereby bringing one face of the sealing ring 15 into alignment with the end face of the tube, and the other opposite face of the sealing ring into alignment with the abutment face of the step in the bore of the seal ring housing. The components are illustrated in Figure 5 in a slightly spaced-apart configuration, for sake of clarity.

Figure 6 illustrates the next stage in the formation of the seal. A ram 27, for example a hydraulic ram, is inserted into the bore of the bottom sub-assembly at the downhole end, and bears against the end 28 of the seal ring housing 14. An axial compressive force is applied by the ram 27 between the end of the seal ring housing 14 and the top sub-assembly 1 to cause engagement of the sealing ring 15 with the end face of the tube 9 and the step arrangement 17 on the seal ring housing to form a seal. The seal ring housing 14 is free to move within the bottom sub-assembly 20, enabling the engagement between the tuning, sealing ring and seal ring housing to be made. Sufficient force is preferably applied to cause deformation of the sealing ring 15. Whilst the force is still being applied, the bottom sub-assembly 20 and the top sub-assembly 1 are screwed together using the threads 7 and 21, in order to maintain the seal once the applied force has been removed.

Figure 7 illustrates a jig 29 for applying such a compressive force. The jig comprises the hydraulic ram 27 and ram actuator 30 connected via legs 31 to a housing 32 having a cavity to support the uphole end 3 of the top sub-assembly. When a force is exerted by the ram on the seal ring housing 14, the legs 31 are held in tension, thereby transmitting a balancing force to the uphole end 3 of the top sub-assembly 1.

Figure 8 illustrates an alternative embodiment of a method of the invention, in cross-sectional view. In this instance, the connection between the tube 9 and a second tubular element 33 is made entirely by dimple connections. The top portion of Figure 8 is shown in a spaced out configuration, for clarity, and illustrates a connector sleeve 34 having a series of threaded holes 4 extending through the wall of the sleeve 34. These holes 4 are preferably disposed around the exterior of the sleeve to provide less point stress. Grub screws 12 are provided to screw into the holes, and have a domed end 35. The external faces of the tube 9 and of the tubular element 33 are provided with indentations 11 at positions corresponding with the holes 4 in the sleeve 34. A sealing ring 15 is provided between the end faces of the tube 9 and the tubular element 33, said ring having the form described above. Having attached one end of the sleeve 34 to the end of either the tube 9 or the tubular element 33 by means of the grub screws, axial compressive force is exerted on the assembly to cause the sealing ring 15 to form a seal between the two end faces. Whilst the force is still present, the sleeve is tightened onto the other element by means of grub screws, thereby maintaining the seal. The applied force can then be removed. The lower portion of Figure 8 illustrates the arrangement once the grub screws 12 have been tightened into position. In embodiments of the method, the tubular element 33 can comprise another length of tubing.

Figures 9 and 10 illustrate a further variant of the method of the invention. Figure 9 shows, in cross-sectional view, a portion of a wall of one end of a length of tubing, and an internal sleeve 36 provided with indentations 11 disposed around its surface. The sleeve 36 is also provided with an outwardly-facing shoulder 38 around its periphery. A connection between the sleeve and the tube may be made by (1) positioning a sealing ring 15 between the end face of the tube 9 and the end face of the shoulder 38; (2) applying an axial compressive force to the tube and sleeve, thereby urging the tube 9 and sleeve 36 together, thereby forming a seal between the tube 9 and the sleeve 36 by crushing the sealing ring 15; (3) applying a point force to the external face of the tube 9 at positions corresponding to the indentations 11, as illustrated by the arrows 37. This causes material from the tube wall 9 to be extruded into the indentations 11, as illustrated in Figure 10, thereby retaining the tube 9 and the sleeve 36 in their sealed relationship. Finally, the axial compressive force may be removed. By this means, an inline connection may be made by use of a face-seating sealing ring on the end of the tube, as described above. In this illustration the sleeve 36 may be a tubular element such as a tool connector.

Figure 11 illustrates a particularly preferred refinement of the end sealing face of a sleeve 36 of the invention. A magnified portion of the apparatus is also shown. This is analogous to that illustrated in Figure 9. In this preferred embodiment, the end sealing face of the shoulder 38 is undercut at an angle Φ relative to the transverse cross-section of the sleeve. The inventor has found that by undercutting the face in this way, a better seal may be formed, as the undercut prevents the sealing ring 15 from being extruded from the gap between the sleeve and the end of the tube 9. The inventors have found that an angle, Φ, of between 10 and 40°, and more preferable between 20 and 30° is particularly effective in this respect.

Figure 12 illustrates the corresponding refinement on the sleeve depicted in Figure 11, used when two tubes are to be joined. Again, a magnified portion of the region including the sealing rings 15 is also shown. In this case, one or both of the seal-abutment faces of the sleeve 40 are also undercut by an angle Φ relative to the transverse cross-section of the sleeve. In an analogous way to as described for the apparatus described in Figure 11, the inventor has found that by undercutting the face in this way, a better seal may be formed, as the undercut prevents the sealing ring 15 from being extruded from the gap between the sleeve and the end of the tube 9. The inventors have found that an angle, Φ, of between 10 and 40°, and more preferable between 20 and 30° is particularly effective in this respect.

Figures 13 and 14 illustrate a further example of the method and apparatus of the invention being used to form an inline connection. Again, the Figures illustrate a cross-section through one wall of a tube assembly to be joined. This example illustrates the joining of two tubes 9 A, 9B. In this example, a sleeve 40 is provided, having indentations 11 disposed about its outer surface. The sleeve 40 is provided with an outwardly-facing ridge 39, having abutment faces on each side. Sealing rings 15 may be located either side of the ridge 39, and the end face of each length of tube 9 A, 9B abutted against the outside faces of each sealing ring. An axial compressive force is then applied to the assembly, urging the tubes 9A

9B together and forming a seal between them by virtue of deformation of the sealing rings 15, sealing against the end faces of the tubes and the abutment faces of the ridge 39. In a method analogous to that described for Figures 9 and 10, dimple connections are again made between the tubes 9A and 9B by applying point forces as indicated by the arrows 37. A portion of the tube wall is forced into the indentations 11, thereby holding the elements in position, as illustrated in Figure 12. The axial compressive force may then be removed. It will be appreciated that the dimple connections may be made to each tube 9A, 9B either successively, or simultaneously.

In any embodiment of the invention, the inventor has found that a particularly effective seal is obtained if a particular design of sealing ring is employed. Figures 15 and 16 illustrate, in perspective and cross-sectional views respectively a preferred sealing ring 15 forming part of the invention. The sealing ring 17 is circular, and is so sized such that the two end faces 41 of the ring are approximately the same size as the end face of a tube 9 to which the device is to be fitted. In this preferred embodiment, each end face is provided with a number of concentric circular grooves 42 extending partway into the ring. These grooves allow the sealing ring to deform more easily when under compressive load, thereby improving the seal. Concentric grooves are preferred over a single spiral groove, as a spiral groove can provide a leakage path in the case of seal failure. By contrast, concentric grooves provide a multiple of seals - one between each groove. Typically between two and eight such grooves will be provided, e.g. four grooves, as illustrated. The sealing ring may be made of soft iron such as that sold under the Registered Trade Mark ARMCO®. Alternatively, the ring may be made of another relatively soft metal, such as aluminium or copper, or an alloy such as those sold under the Registered Trade Marks INCONEL® (alloys containing predominantly nickel and chromium) or MONEL® (alloys containing predominantly nickel and copper). In particularly preferred embodiments, however, the ring is manufactured from the same material from which the tube 9 is constructed. In this way, any unwanted electrolytic effects are avoided.

Figure 17 illustrates a further preferred arrangement for connecting an assembly to a tube 9. In this arrangement, the sleeve 36 is again provided with indentations 11 that will serve to receive the dimpled tube. A sealing ring 15 is placed between the end face of the tube 9 and a compressions ring 43. The compression ring 43 may also be provided with an undercut sealing face as described in relation to Figures 11 and 12. Once a compressive force has been applied to urge the sleeve 36 towards the end of the tube 9, thereby forming a seal by means of the sealing ring 15, against pre-load ring 44 and the downhole face of the compression ring 43 thereby holding it in position, a pre-load ring 44 may be tightened against the downhole face of the compression ring 43 thereby holding it in position, under compression, while the dimple connection is made (as shown in Figure 18). Once the connection is made, a lock nut 45 may be tightened against the pre-load ring 44 to further secure the assembly. In Figures 17 and 18, each element of the assembly is shown in a slightly spaced-apart configuration, for clarity. The downhole assembly connection is also omitted, for clarity. Figure 19 illustrates, in schematic form, an assembly jig and a method of forming a connection between a tube 9 and a tubular element, in this example a connector for a downhole tool assembly. The elements are shown partially schematically, and in a spaced-apart configuration, for clarity.

There is provided a gripper unit 46 configured to grip the outside of the tube 9, to resist an axial compressive force to be exerted on the assembly to aid sealing. The skilled addressee will be able to readily choose an appropriate arrangement for a gripper unit, but the inventor has found it particularly effective to use a collet having inwardly-facing teeth to grip the outer surface of the tube 9, said collet having a tapered outer surface, in combination with outer ring having a corresponding tapered surface that can be screwed onto a ring support causing the collet to grip the outer surface of the tube. Adjacent the gripper unit 46 is a dimple connector jig 47, known in the art, which can apply point pressure to the tube 9 via a number of dimple presses 48 to form a dimple connection between the tube 9 and the inner sleeve 20.

Adjacent the dimple connector jig 47 is a spacer unit 49, of generally cylindrical construction, and preferably furnished with a window arrangement 50 (comprising an aperture in the spacer unit 49) to allow visual inspection of the operation of a ram 27. The window arrangement 50 allows access to the connection, should a lock nut assembly, illustrated in Figs 17 and 18 be used. Finally, adjacent the spacer unit 49 is a ram 27 and ram actuator 30 that may be used to exert axial compression on the assembly, causing the sealing ring 15 to seal between the end faces of the tube 9 and inner sleeve 20. Whilst the seal abutment face of the inner sleeve 20 is illustrated with a flat transverse face, this may also be undercut, as discussed above.

All of the elements in Figure 19 are illustrated in a spaced-apart configuration, for clarity, and are shown as being unconnected, again for clarity. In operation, the individual units (gripper unit 46, dimple connector 47, spacer unit 49, and ram actuator 30) are preferably connectable, e.g. by screw threads, to allow the unit to be assembled (preferably in a vertical orientation) on the end of a length of coil tubing.

Figure 20 illustrates the assembly of Figure 19 after formation of the dimple connection.

In operation, the gripper unit grips the outside face of the tube 9, and the dimple connector 47, spacer unit 49 and ram assembly 27, 30 are assembled on the end of coil tube 9 with the inner sleeve 20 in place. The ram is actuated to compress the sealing ring 15 and form the seal. Any lock nuts (as illustrated in Fig 17 and 18) are tightened, and then pressure is applied to the tube 9 to form the dimple connections.

Claims

1. A method of connecting a tube to a tubular element, said method comprising the steps of:

abutting an end face of the tube to a first face of a sealing ring;

abutting an end face of the tubular element to a second, opposite, face of said sealing ring;

applying an axial compressive force to urge the tube towards the tubular element, thereby compressing said sealing ring to form a seal between the tube and the tubular element;

connecting said tube to said tubular element by means of a connector to maintain said compressive force sufficiently to maintain the seal so formed;

wherein said connector is attached to said tube by means of a dimple arrangement.

2. A method according to Claim 1 wherein said tubular element comprises a second tube.

3. A method according to Claim 1 wherein said tubular element comprises a downhole tool connector.

4. A method according to any preceding claim wherein said dimple arrangement is created by:

forming indentations on an outside surface of said tube;

locating said connector around the outside of the tube; and

attaching the connector to the tube by means of grub screws that engage with said indentations.

5. A method according to any of claims 1 to 3 wherein said dimple arrangement is created by:

providing a connector with indentations on its outside surface;

locating said connector within the bore of the tube; and applying point loads to the tube at points corresponding to said indentations, thereby causing the tube wall to engage with said indentations.

6. Apparatus for use in a method according to any of claims 1-4 comprising:

(a) a top sub-assembly having an aperture therethrough to allow it to be passed over a tube to be connected, a plurality of threaded holes passing through the wall of the top sub-assembly to allow grub screws to be inserted to engage with the outside of a tube within the top sub-assembly, and a thread at one end for connection to a bottom sub-assembly;

(b) a bottom sub-assembly comprising a thread at one end for connection to said top sub-assembly, a tool connector at the other end, and a cavity to accommodate a seal ring housing;

(c) a seal ring housing having an aperture therethrough to accommodate the end of a tube to be connected; and

a step within the bore of the housing to form an abutment face for a sealing ring.

7. Apparatus according to Claim 6 wherein said seal ring housing has a tapered portion on its external surface; said bottom sub-assembly cavity has a

correspondingly tapered configuration; and an Ό'-ring groove is provided on the external surface of said seal ring housing or the internal surface of said cavity to allow an Ό'-ring seal to be formed between them.

8. A method of connecting a tube to a tubular element substantially as described herein, with reference to and as illustrated by any appropriate combination of the accompanying drawings.

9. Apparatus for use in a method of connecting a tube to a tubular element substantially as described herein, with reference to and as illustrated by any appropriate combination of the accompanying drawings.