Riser system

Abstract

A riser system configured to be secured between a surface vessel and a subsea location comprises a primary conduit and an auxiliary conduit extending adjacent the primary conduit, wherein the primary and auxiliary conduits are connected together at an axial location along the riser system via a connecting portion. The auxiliary conduit comprises a composite material formed of at least a matrix and one or more reinforcing elements embedded within the matrix.

Claims

1. A riser system configured to be secured between a surface vessel and a subsea location, said system comprising: a continuous unitary primary conduit; and a continuous unitary auxiliary conduit extending adjacent the primary conduit and comprising a composite material formed of at least a matrix and one or more reinforcing elements embedded within the matrix, wherein the primary and auxiliary conduits are connected together at an axial location along the riser system via a connecting portion, said auxiliary conduit being pretensioned relative to the connecting portion.

2. The riser system according to claim 1, comprising or defining a drilling riser system.

3. The riser system according to claim 1, wherein the primary and auxiliary conduits are rigidly connected together at or via the connecting portion to prevent or restrict relative movement of the auxiliary and primary conduits in at least one plane or direction at the connecting portion.

4. The riser system according to claim 3, wherein rigidly connecting the primary and auxiliary conduits permits load transference between the primary and auxiliary conduits across the connecting portion.

5. The riser system according to claim 1, wherein the auxiliary conduit at least partially supports the weight of the primary conduit.

6. The riser system according to claim 1, wherein the auxiliary conduit is pretensioned relative to the connecting portion to establish pre-compression within the primary conduit.

7. The riser system according to claim 1, comprising a plurality of connecting portions permitting the auxiliary conduit to be connected relative to the primary conduit at multiple points along the length of the riser system.

8. The riser system according to claim 7, wherein the auxiliary conduit is pre-tensioned between two axially spaced connecting portions.

9. The riser system according to claim 1, comprising a plurality of continuous unitary auxiliary conduits circumferentially distributed about the primary conduit.

10. The riser system according to claim 9, wherein the plurality of auxiliary conduits are evenly circumferentially distributed about the primary conduit.

11. The riser system according to claim 1, wherein the primary conduit comprises a composite material formed of at least a matrix and one or more reinforcing elements embedded within the matrix.

12. The riser system according to claim 11, wherein the primary and auxiliary conduits comprise a similar composite material.

13. The riser system according to claim 1, wherein at least the auxiliary conduit comprises a variation along a length of the auxiliary conduit.

14. The riser system according to claim 13, wherein at least one axial portion of the auxiliary conduit varies relative to a different axial portion of the auxiliary conduit.

15. The riser system according to claim 13, wherein at least the auxiliary conduit comprises a variation in axial load carrying capacity or specification along the length of the auxiliary conduit.

16. The riser system according to claim 13, wherein an upper region of the auxiliary conduit is configured to accommodate greater axial load than a lower region of the auxiliary conduit.

17. The riser system according to claim 1, wherein at least the auxiliary conduit comprises a wall comprising the composite material, wherein the wall comprises or defines a local variation in construction to provide a local variation in a property of the auxiliary conduit.

18. A method for forming a riser system to be secured between a surface vessel and a subsea location, comprising: providing a continuous unitary primary conduit; extending a continuous unitary auxiliary conduit adjacent the primary conduit, wherein the auxiliary conduit comprises a composite material formed of at least a matrix and one or more reinforcing elements embedded within the matrix; connecting the primary and auxiliary conduits together at an axial location along the riser system via a connecting portion; and pre-tensioning the auxiliary conduit relative to the connecting portion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a diagrammatic illustration of a drilling riser system in accordance with an aspect of the present invention;

(3) FIG. 2 is an enlarged view of a portion of the drilling riser system of FIG. 1;

(4) FIG. 3 is a lateral cross-sectional view of the drilling riser system taken through line 3-3 in FIG. 2;

(5) FIG. 4A is an illustration of an individual joint of the drilling riser system shown in an unloaded configuration;

(6) FIG. 4B is an illustration of the individual joint of FIG. 4A exposed to axial tension;

(7) FIG. 4C is an illustration of the individual joint of FIG. 4A exposed to axial bending;

(8) FIG. 5A is an illustration of an individual joint of the drilling riser shown in a pre-stressed configuration;

(9) FIG. 5B is an illustration of the individual joint of FIG. 5A shown in use;

(10) FIG. 6 is an illustration of a drilling riser system in accordance with an alternative embodiment of the present invention;

(11) FIG. 7 is an enlarged longitudinal cross-sectional view in the region of a connection portion/interface assembly of a riser system in accordance with an embodiment of the present invention;

(12) FIG. 8 is an enlarged view of a portion of a connection portion/interface assembly of as riser system in accordance with an alternative embodiment of the present invention;

(13) FIG. 9 is an enlarged view of a portion of a connection portion/interface assembly of a riser system in accordance with a further alternative embodiment of the present invention;

(14) FIG. 10 is an enlarged view of a portion of a connection portion/interface assembly of a riser system in accordance with a still further alternative embodiment of the present invention;

(15) FIG. 11 is an enlarged view of a portion of a connection portion/interface assembly of a riser system in accordance with another alternative embodiment of the present invention;

(16) FIG. 12 is an enlarged view of a portion of a connection portion/interface assembly of a riser system in accordance with a further alternative embodiment of the present invention;

(17) FIG. 13 is an illustration of a riser system in accordance with another embodiment of the present invention;

(18) FIGS. 14 to 17 are enlarged views of a portion of a connection portion/interface assembly which may be suitable for use in the riser system of FIG. 13 in accordance various embodiments of the present invention;

(19) FIG. 18 provides an illustration of a method of installing an auxiliary conduit relative to a primary conduit; and

(20) FIG. 19 provides an illustration of an alternative method of installing an auxiliary conduit relative to a primary conduit.

DETAILED DESCRIPTION OF THE DRAWINGS

(21) A riser system, generally identified by reference numeral 10, in accordance with an embodiment of the present invention is illustrated in FIG. 1. The riser system may be for any appropriate use. However, for the purposes of the present example the riser system is a drilling riser system. The riser system 10 extends between a surface vessel 12, which in the present embodiment is a drilling ship, and a subsea wellhead 14 (which may include a BOP 15). The drilling riser system 10 comprises a central large bore primary conduit 16 and a plurality of smaller auxiliary conduits 18 which are circumferentially distributed around the primary conduit 16. The auxiliary conduits 18 are mechanically and rigidly secured to the primary conduit at or via a plurality of axially arranged connecting portions 20. In use, the primary conduit 16 accommodates drilling equipment and certain fluids, such as drilling mud and the like, whereas the auxiliary conduits 18 accommodate the communication of other fluids between the surface vessel 12 and the wellhead 14. Such other fluids may include well kill fluids, purge fluids, choke fluids, control fluids for operation of subsea or wellbore equipment, such as the BOP 15 and the like.

(22) Reference is now additionally made to FIGS. 2 and 3, wherein FIG. 2 is an enlarged view in the region 21 of FIG. 1, and FIG. 3 is a lateral cross-sectional view taken through line 3-3 of FIG. 2.

(23) The riser system 10 is formed from a plurality of individual riser joints 22 which are secured together in end-to-end relation via the connecting portions 20. Each joint 22 includes a discrete primary conduit section 16a and a plurality of discrete auxiliary conduit sections 18a. Opposite ends of each joint 22 include a respective flange component 20a, 20b to which the primary conduit section 16a and auxiliary conduit sections 18a are rigidly secured. As will be described below, such a rigid connection between the conduit sections 16a, 18a results in load transference therebetween. In some circumstances this may permit the auxiliary conduits 18 to support some of the weight of the primary conduit 16.

(24) With particular reference to FIG. 2, the flange components 20a, 20b of adjacent joints 22 are secured together, for example by bolts (not shown) to establish a rigid connection between the individual joints 22 at a connecting portion 20. The individual flange components 20a, 20b of each connecting portion 20 may establish both mechanical and fluid connection between the individual primary and auxiliary conduit sections 16a, 18a. Although flange-type connectors are illustrated, other types of connection may be possible to secure the individual joints 22 together, such as bayonet type fittings, stab-in type fittings, threaded fittings, clamped fitting or the like.

(25) Each adjacent auxiliary conduit section 18a is connected together at the connecting portion via respective interface assemblies 23, wherein in the present embodiment the interface assemblies 23 provide a rigid connection between respective pairs of adjacent auxiliary conduit sections 18a. Example embodiments of such interface assemblies 23 will be described later below. In the present embodiment such interface assemblies 23 are provided at the region of the connecting assembly 20. However, in other embodiments an interface assembly may be provided remotely from the connecting portion 20, such that connection of at least two discrete auxiliary conduits need not exist at a connecting portion 20.

(26) In the present invention at least one and in some embodiments all of the auxiliary conduits 18 comprise or are formed from a composite material of at least a matrix and one or more reinforcing elements embedded within the matrix. As will be described in detail below, composing the auxiliary conduits 18 of a composite material provides significant advantages over known arrangements, for example in arrangements in which metallic auxiliary lines are utilised.

(27) In the present embodiment the primary conduit 16 may be formed of a metallic material. However, in other embodiments the primary conduit 10 may be formed of a composite material. Also, in the present embodiment the connecting portions 20 may be formed of a metallic material. However, in other embodiments at least one of the connecting portions 20 may be formed of a composite material.

(28) The riser system 10 will be subject to various operational loads during use, which are illustrated with respect to FIGS. 4A to 4C. In FIG. 4A a single riser joint 22 is illustrated in an unloaded configuration. During use, the joint 22 may be subject to significant tension, as illustrated in FIG. 4B, which may be generated by the weight of the riser system 10 (in increasing water depths the weight of the system can be significant). As the primary and auxiliary conduit sections 16a, 18a are rigidly secured relative to the flange components 20a, 20b, such tensile forces will generate axial strain within these conduit sections 16a, 18a, as illustrated in an exaggerated manner in FIG. 4B.

(29) Also during use the joint 22 may be subject to bending, as illustrated in FIG. 4C. Due to the rigid connection of the primary and auxiliary conduit sections 16a, 18a via the flange components 20a, 20b, and because the auxiliary conduit sections 18a are located offset from the longitudinal bending axis, opposing auxiliary conduit sections 18a will be exposed to different levels of strain. That is, one auxiliary conduit may be subject to axial tension, as illustrated by arrows 25, whereas an opposing auxiliary conduit may be subject to axial compression as illustrated by arrows 27.

(30) The present invention may permit such strains during load transference between the primary and auxiliary conduits 16, 18 to be accommodated by forming the auxiliary conduit from a composite material. That is, the use of a composite material may permit increased levels of strain to be accommodated such that the auxiliary conduits may be suitably compliant during such periods of deformation, preventing or minimising failure, such as tensile failure, buckling or the like. More specifically, the composite material may exhibit a higher strain rate to specific stress than an equivalent metallic component. Accordingly, the composite material may permit the auxiliary conduits 18 to satisfactorily accommodate deformation, such as may be caused by tensile forces, compressive forces, bending forces, torsional forces and the like. The composite material of the auxiliary conduits 18 may be configured to withstand or permit axial and/or bending strains of up to 6%, up to 4%, up to 2% or up to 1%. Such maximum permitted strains for the composite material may be significantly larger than a maximum permitted strain for a conventional material such as steel, aluminium or the like. Accordingly, an auxiliary conduit 18 comprising such a composite material may provide a compliant conduit by virtue of the properties of the composite material alone. This may reduce or eliminate the requirement for additional measures to protect the auxiliary conduits from excessive strains.

(31) The composite material of the auxiliary conduits 18 may provide an inherent increase in elastic recovery properties. Accordingly, any deformation, such as buckling, while under load may only be temporary. This may assist in maintaining the auxiliary conduits in a non-deformed state when in a no-load condition, which may assist in handling, disassembly and re-use of the auxiliary conduits, for example.

(32) Increasing water depths will also expose the riser system 10 to increasing pressures, such as hydrostatic pressures, which will typically be manifested as hoop strain within the conduits 16, 18 of the riser system 10. The requirement to accommodate pressure originating loading, and axial loading such as tension and compression, may necessitate the use of very thick-walled conduits, which in turn may add significantly to the weight of the entire system. In some cases such design requirements may result in the operational capacity of the vessel 12 (FIG. 1) being exceeded.

(33) Further, differential strain applied to different auxiliary members 18 may place significant loading, particularly bending, on the connecting portions 20. Providing auxiliary conduits 18 composed of composite material may allow a larger strain rate to specific stress within the auxiliary conduits, permitting greater axial extension of said conduits and thus assisting to protect the connecting portions 20.

(34) Furthermore, forming the auxiliary conduits 18 from a composite material may assist to minimise the weight of the system, for example relative to all metal riser systems known in the art. This may permit thicker-walled conduit sections to be utilised without exceeding weight limits, such as may be dictated by the surface vessel 12.

(35) As described above and illustrated in the drawings, in the exemplary embodiment the primary and auxiliary conduit sections 16a, 18a of a riser joint 22 are rigidly secured between respective flange components 20a, 20b. In the present exemplary embodiment one or more of the auxiliary conduit sections 18a are connected to the respective flange components 20a, 20b (via appropriate interface assemblies 23 or components thereof) such that a pretension is applied within the auxiliary conduit section 18a. Such a pre-tension arrangement is illustrated with respect to FIGS. 5A and 5B.

(36) FIG. 5A illustrates a single pre-stressed riser joint 22 prior to installation within the riser system 10, wherein pre-tension within the auxiliary conduit sections 18a, illustrated by arrows 29, is established between the flange components 20a, 20b. Due to the rigid connection between the auxiliary conduit sections 18a and the primary conduit section 16a, this pre-tension establishes a degree of pre-compression within the primary conduit section 16a, as illustrated by arrows 31. When the pre-stressed riser joint 22 is installed within the riser system 10 as illustrated in FIG. 5B, the joint 22 will become exposed to global tensile loading due to the weight of the system 10 below said joint 22. This global tension will establish further tension and thus strain within the auxiliary conduit sections 18a, as illustrated by larger arrows 29a. However, forming the auxiliary conduits 18 from a composite material will permit such increased levels of strain to be accommodated. Further, as the primary conduit section 16a is initially pre-compressed, this section 16a may only be exposed to a significantly lower degree of tension, as illustrated by smaller arrows 31a, thus providing protection to the primary conduit section 16a.

(37) As suggested above, any additional axial extension deformation or strain affecting the auxiliary conduit sections 18a, for example due to the global weight of the assembled riser 10 or during dynamic loading, will result in further tension being applied within the auxiliary conduit section 18a. However, due to the composite construction of the auxiliary conduit sections 18a this eventuality is accepted due to the composite material exhibiting a higher strain rate to specific stress than, for example, an equivalent metallic component. It is understood that in conventional riser arrangements, such as where metallic auxiliary lines are utilised, pre-tensioning is intentionally avoided or minimised where additional tension is expected during use. For example, as metallic components are generally axially stiff, an initial level of pre-tension may minimise the available accommodation of axial extension deformation during dynamic conditions, as stress will increase significantly for very little increase in axial strain.

(38) The pre-tension within the auxiliary conduits 18a may effectively permit the auxiliary conduits 18 to share some of the axial loading within the riser system 10 with the primary conduit 16. That is, pre-tensioned auxiliary conduits 18 may function to support at least a portion of the weight of the primary conduit 16. Such an arrangement may permit the primary conduit 16 to be reduced in size, providing a number of benefits such as weight reduction, cost reduction and the like.

(39) Pre-tension within the auxiliary conduit sections 18a may be selected such that load sharing with the primary conduit is achieved at all times during use. As such, even in the event of dynamic loading the primary conduit 16 will always be structurally assisted in accommodating the applied loads.

(40) Providing a pre-tension within one or more of the auxiliary conduits 18 may also provide protection to the auxiliary conduit 18 during compression thereof. That is, an deformation which would normally result in compression will be initially absorbed by relaxation of the pretension and corresponding strain.

(41) Providing a pre-tension may also provide benefits during bending of the riser system, such as illustrated in FIG. 4C. For example, the composite material may permit a pretension to be achieved within the auxiliary conduits 18 which is of a sufficient magnitude that even under the bending condition as in FIG. 4C all auxiliary conduits 18 always remain in tension. This may prevent any state of compression from occurring.

(42) In the riser system 10 first illustrated in FIG. 1 the auxiliary conduits 18 are of uniform construction. However, in other embodiments the auxiliary conduits 18 may vary in construction, for example along their length. Such variation in the auxiliary conduits 18 may be intended to tailor the riser system more closely with operational conditions. For example, during use an upper region of a riser system will be exposed to greater weight than a lower region. The present invention may tailor a riser system to such conditions by, for example, varying the axial construction of one or more auxiliary conduits such that upper regions are capable of supporting greater axial tension and associated strains than lower regions. An exemplary embodiment of such variation is illustrated in FIG. 6, in which upper regions of an auxiliary conduit 18 include a thicker wall than lower regions.

(43) In other embodiments such variation may be achieved by a variation in the construction of the composite material.

(44) Further, other conditions may be accommodated. For example, it will be recognised that lower auxiliary conduit regions will be subject to larger local pressure forces due to increased water depths. As such, lower regions of an auxiliary conduit may be configured to resist larger hoop forces than upper regions.

(45) The primary conduit of a riser system may also include similar constructional variations to be more closely tailored to specific conditions.

(46) As noted above, each adjacent auxiliary conduit section 18a is connected relative to each other at the connecting portion via respective interface assemblies 23. There are a number of possible arrangements of such interface assemblies 23, some of which will be described below.

(47) One such exemplary interface assembly or arrangement 23 is shown in FIG. 7, which is a cross-sectional view of the riser system 10 in the region of a connecting portion 20. It should be noted that connection of each adjacent auxiliary conduit section 18a may be achieved using the same form of connection or interface assembly, or via different connection or interface assemblies. To demonstrate this possibility only an interface assembly 23 associated with a lower auxiliary conduit section 18a and corresponding connecting portion 20b are illustrated in any detail; the upper conduit section 18a and connecting portion 20a are simply shown in broken outline.

(48) In this embodiment the end region of the lower auxiliary conduit section 18a extends through flange component 20b. A wedge or conical profiled portion 24 is defined on the end of the auxiliary conduit section 18a which is received within a corresponding profile 26 formed within flange component 20b. As such, the flange component 20b and connecting portion 20 define integral parts of the interface assembly 23. In the illustrated embodiment the wedge profiled portion 24 is integrally formed with the end of the conduit 18a. In this way, the auxiliary conduit section 18a may be robustly secured at the connecting portion 20. Further, this arrangement can permit the auxiliary conduit section 18a to transmit a load, such as a tensile load, between respective flange components 20a, 20b of a riser joint 22.

(49) As the wedge portion 24 is to be captivated by the profile 26 formed in the lower connecting portion 20b, the lower conduit section 18a will be installed by being inserted through the connecting portion 20b from above. The opposite end of the auxiliary conduit 18a may be secured to a lower connecting portion 20 (not shown in FIG. 7) via an appropriate further interface assembly, examples of which will be described later. It should be understood that any further interface assembly might also need to be passed through the lower connector 20b shown in FIG. 7 and dimensional considerations in this regard may need to be taken into account.

(50) Although not illustrated, a sealing arrangement may be provided between the flange components 20a, 20b and/or the conduit sections 18a. Also, in some embodiments the composite material of the auxiliary conduit sections 18a may permit inherent compliance upon engagement together to provide appropriate sealing.

(51) In the embodiment shown in FIG. 7 the end one or both auxiliary conduits 18a extend through the respective flange components 20a, 20b and are captivated within an appropriate profile 26. However, in other embodiments the ends of at least one auxiliary conduit may be secured externally of the flange components. Such an embodiment is shown in FIG. 8, which is generally similar to the arrangement shown in FIG. 7 and as such like components share like reference numerals, incremented by 100. It may be the case that each flange component includes a different type of association or engagement with a respective auxiliary conduit section. Accordingly, only a single flange component 120b is illustrated in FIG. 8.

(52) As in the embodiment shown in FIG. 7, the interface assembly 123 of FIG. 8 also generally includes a profile 124 formed in the end of an auxiliary conduit section 118a, and a profile 126 formed in the associated flange component 120b. However, in the present interface assembly 123 an interface component 1 is provided which is interposed between the auxiliary conduit section 118a and flange component 120b. Specifically, the interface component 1 includes a first profiled portion 2 which captivates the profiled end 124 of the auxiliary conduit section 118, and a second profiled portion 3 which is engaged and captivated within the profile 128 in the flange component 120b.

(53) An alternative interface assembly 223 is shown in FIG. 9, reference to which is now made. The general arrangement shown in FIG. 9 is similar to that shown in FIG. 7 and as such like components share like reference numerals, incremented by 200. Thus, a connecting portion 220 is composed of a pair of flange components 220a, 220b which permit primary conduit sections 216a and auxiliary conduit sections 218a to be coupled together. Each flange component 220a, 220b comprises an interface component 30 which forms part of the interface assembly 223 (the upper auxiliary conduit section 118a is shown disconnected to illustrate the interface component 30). The interface component 30 comprises a quick connect profile 32 which may engage a corresponding profile within the end 34 of the auxiliary conduit section 218a. In this respect the corresponding profile within the auxiliary conduit section 218a may be integrally formed therewith, or alternatively may be provided on a separate component which itself is secured to the end 34 of said conduit section 218a. The end 34 may define an adaptor portion configured to permit connection of the auxiliary conduit sections 218a to conventional or existing connections. Furthermore, in the illustrated embodiment the interface component 30 is defined as a male component which is received within a female end 34 of an auxiliary conduit section 218a. However, in other embodiments the interface component may define a female socket configured to receive a male portion formed on the end 34 of the auxiliary conduit section 218a, for example in the form of a stab-in type connector.

(54) In the embodiment shown in FIG. 9, the connected flange components 220a, 220b of the connecting portion 220 may define an internal flow path configured to fluidly couple adjacent (upper and lower) auxiliary conduit sections 218a. Such an internal flow path may form part of the interface assembly 223.

(55) The embodiment shown in FIG. 9 provides a quick-type connection for the auxiliary conduit 218a. However, other types of connection may be possible, such as illustrated in the embodiment shown in FIG. 10. In this respect FIG. 10 provides an enlarged view in the region of an interface assembly 323, which includes, at least, a portion of a flange component 320a of a connecting portion 320. It should be noted that the arrangement shown in FIG. 10 is generally similar to that shown in FIG. 7 and as such like components share like reference numerals, incremented by 300.

(56) The interface assembly 323 includes an interface component 40 which is secured to the flange component 320a, for example by a threaded connection, interference fit, welding, integrally forming or the like. The end of an associated auxiliary conduit section 318a includes a profiled region 324. The assembly 323 further includes a collar 42 which defines a captive profile 44 at one end for captivating the end profile 324 of the auxiliary conduit section 318a, and a thread 46 at an opposite end for threadably engaging with the interface component 40. Accordingly, the collar 42 may be used to secure the conduit section 318a to the interface component 40. Furthermore, the threaded connection between the collar 42 and interface component 40 may permit a degree of tension, such as pre-tension, to be established within the auxiliary conduit section 318a.

(57) In an alternative embodiment the functionality of the interface component 40 and collar 42 shown in FIG. 10 may be provided by a single component. Such an arrangement is shown in FIG. 11, which is similar in many respects to the arrangement shown in FIG. 7 and as such like features share like reference numerals, incremented by 400. In this embodiment the interface assembly 423 comprises an interface component 50 which includes a captive profile region 52 which engages and captivates a profile 424 formed on the end of an auxiliary conduit section 418a. An opposite end of the interface component 50 comprises a thread portion 54 to permit a threaded connection with flange component 420a. Such a threaded connection may permit the interface component 50 to establish tension within the auxiliary conduit section 418a.

(58) A further alternative embodiment of an interface assembly 523 is illustrated in FIG. 12, reference to which is now made. The arrangement in FIG. 12 is generally similar to that shown in FIG. 7 and as such like components share like reference numerals, incremented by 500. Thus, a connecting portion 520 is composed of a pair of flange components 520a, 520b which permit primary conduit sections (not illustrated) and auxiliary conduit sections 518a to be coupled together. The end of each adjacent auxiliary conduit section 518a includes an integrally formed composite connecting profile 60 (the connecting profile could alternatively be a separate component) which permits the end regions 62 of the auxiliary conduit sections 518a to be connected to a respective flange component 520a, 520b. In the illustrated embodiment each connecting profile 60 comprises a number of holes 64 for permitting a bolted connection with an associated flange component 520a, 520b.

(59) It should be understood that a combination of interface assemblies may be utilised. For example, an interface assembly similar to that shown in FIG. 7 or 8 may be present at an upper connecting portion, and an interface assembly similar to that shown in FIGS. 10 and 11 may be present at a lower connecting portion, or vice versa.

(60) The embodiments described above provide a rigid connection between the primary and auxiliary conduits within a riser system. Such a rigid connection may provide advantages such as permitting the auxiliary conduits to load share with the primary conduit, to allow the auxiliary conduits to be pre-tensioned and the like. However, in other embodiments such a connection may be compliant. For example, while a general connection, or at least an association, may exist between primary and auxiliary conduits, this may permit relative movement of said conduits in one or more planes or directions, as will be demonstrated below, initially with reference to FIG. 13 which illustrates a portion of a riser system, generally identified by reference numeral 610.

(61) The riser system includes a primary conduit 616 and a plurality of auxiliary conduits 618 which run axially alongside the primary conduit. As illustrated by arrows 70 the auxiliary conduits 618 are permitted to move axially, or float, relative to the primary conduit 616.

(62) The riser system 610 is formed from a plurality of riser joints 622 which are secured together in end to end relation at a connecting portion 620. Each riser joint 622 includes a discrete primary conduit section 616a and a plurality of discrete auxiliary conduit sections 618a, wherein each conduit section 616a, 618a extends between opposing flange components 620a, 620b. Opposing flange components 620a, 620b of adjacent riser joints 622 are connected together to define respective connecting portions 620. A clamping arrangement 72 is provided intermediate individual flange components 620a, 620b of each riser joint 622 and functions to clamp or retain the auxiliary conduit sections 618a within proximity to the primary conduit section 616a.

(63) A form of connection or interface assembly 623 is provided between adjacent auxiliary conduit sections 618a generally in the region of the connecting portions, wherein the interface assemblies 623 permit relative axial movement of adjacent and connected auxiliary conduit sections 618a. Many different forms of such an interface assembly is possible within the scope of the present invention and some example embodiments are presented below.

(64) Such an example interface assembly 623 is illustrated in FIG. 14, wherein the assembly includes an interface component 74 comprising respective tubular spigot portions 76 located on opposing sides of a flange 78, creating a general double top-hat profile. In the present embodiment the flange 78 is clamped between opposing flange components 620a, 620b of the connecting portion 620. However, such a connection may not be required.

(65) Each tubular spigot portion 76 is received within the end of a respective auxiliary conduit section 618a with sealing being achieved via seals 80. The arrangement is such that a telescoping movement, illustrated by arrows 82, between the auxiliary conduit sections 618a and respective spigot portions 76 is permitted, providing a degree of relative axial movement between the adjacent conduit sections 618a.

(66) In the embodiment illustrated in FIG. 14 the interface component 76 represents a restriction in internal diameter relative to the auxiliary conduit sections 618a. However, in other embodiments such a restriction may be avoided or minimised, for example as illustrated in FIG. 15 which shows a slightly modified interface assembly, shown removed or isolated from a connecting portion (although it should be clear that any interface assembly may be located remotely from a connecting portion). In view of the significant similarities between the embodiments shown in FIGS. 14 and 15, like components share like reference numerals. As such, in FIG. 15 the interface assembly is also identified by reference numeral 623 and includes an interface component 74 having opposing tubular spigot portions 76 to be received in a sliding manner within the ends of respective auxiliary conduit sections 618a. However, in the present embodiment the ends of the auxiliary conduit sections 618a include enlarged diameter regions 84 which receive the respective spigot portions 76 to permit a more uniform internal bore 86 to be created.

(67) In other embodiments the use of a separate interface component, such as illustrated in FIGS. 14 and 15, may not be required. For example, it may be possible for the ends of adjacent auxiliary conduit sections to be directly engaged, for example in a telescoping manner. Such an interface assembly 723 is illustrated in FIG. 16, wherein the end of one auxiliary conduit section 718a (the upper conduit in this example) is inserted within the end of an adjacent auxiliary conduit section 718a (the lower conduit in this example) with sliding seals 88 provided therebetween.

(68) In a similar manner to that described above with reference to FIG. 15, arrangements may be made to permit a more uniform internal diameter to be retained. Such arrangements are disclosed in FIG. 17, where the end of one auxiliary conduit section 718a (the upper section in this example) includes a reduced outer diameter section 90, and the end of the other auxiliary conduit section 718a (the lower section in this example, includes an enlarged internal diameter region 92.

(69) In various embodiments described above, such as with reference to FIGS. 2 and 13, a riser joint 22 (622) generally includes a primary conduit section 16a (616a) and a number of auxiliary conduit sections 18a (618a) secured between opposing flange components 20a (620a), 20b (620b). FIGS. 18 and 19 provide illustrations of alternative embodiments for installing an auxiliary conduit section 18a (618a) relative to opposing flange components 20a (620a), 20b (620b).

(70) Referring initially to FIG. 18, an auxiliary conduit section 18a (618a) may be axially inserted through the upper (or lower in other embodiments) flange component 20b (620b).

(71) Alternatively, as shown in FIG. 19, an auxiliary conduit section 18a, (618a) may be longitudinally deformed to reduce its axial envelope length using a deforming apparatus 98. While in this deformed state the auxiliary conduit section 18a (618a) may be located between the flange components 20a (620a), 20b (620b) and subsequently relaxed to then be retained between said flange components. In such an arrangement the composite material of the auxiliary conduit section 18a (618a) may permit such longitudinal deformation or bending to be achieved by the apparatus 98 without causing damage or creating significant stress within the conduit, and also permit substantially complete elastic recovery when relaxed during insertion between the flange components.

(72) It should be understood that the embodiments described herein are merely exemplary and that various modifications may be made thereto. For example, the riser system is not limited for use as a drilling riser system. Furthermore, the principles of the invention need not only be applied to riser systems, and may be utilised within conduit systems which comprise multiple individual conduits running alongside each other.

(73) Furthermore, in the embodiments described above the auxiliary conduits are established by a number of discrete conduit sections joined together at the connecting portions. However, in other embodiments a continuous length of auxiliary conduit may be provided. In such an arrangement the continuous conduit may extend through a connecting portion, for example through a suitably dimensioned throughbore or the like.

(74) Many different embodiments of connection or interface between auxiliary conduit sections has been presented. However, any suitable combination of such embodiments may also be possible. For example, one end of an auxiliary conduit section may be associated with one type or form of connection or interface, whereas an opposite end may be associated with a different type or form of connection or interface.