WO2016092311A1

WO2016092311A1 - Composite component deployment configurations

Info

Publication number: WO2016092311A1
Application number: PCT/GB2015/053783
Authority: WO
Inventors: Stephen Hatton
Original assignee: Magma Global Limited
Priority date: 2014-12-10
Filing date: 2015-12-10
Publication date: 2016-06-16
Also published as: GB2533123A; GB201421957D0

Abstract

A riser system and associated method of deployment, the riser system comprising a riser (10) to be secured between a floating body (20) and a subsea location (70), the riser comprises a composite material formed of at least a matrix and one or more reinforcing elements embedded within the matrix; the riser system being arranged such that, in use, the riser comprises or defines: a lower portion (75) extending from the subsea location; an upper portion extending from the floating body (85); and a bend (80) or elbow between the lower and upper portions. Optionally, the riser system further comprises one or more buoyancy elements (50), wherein one or more or each of the buoyancy elements are attached to or arranged to form or support the bend or elbow, wherein at least one or each of the buoyancy elements are optionally variable buoyancy elements having selectively variable or changeable buoyancy and are optionally selectively switchable or reconfigurable between at least a non-buoyant or less buoyant state and a buoyant or more buoyant state by inflating and/or deflating one or more or each of the buoyancy elements.

Description

COMPOSITE COMPONENT DEPLOYMENT CONFIGURATIONS

FIELD OF THE INVENTION

The present invention relates to various deployment configurations for subsea composite components, such as risers.

BACKGROUND

Risers are commonly used in applications, such as oil and gas related operations, to transport fluids such as oil, gas and injections fluids between a sea bed and a surface vessel.

One known riser configuration is a single line offset riser (SLOR), which comprises a substantially vertical steel pipe, one end of which is anchored at a sea bed location, e.g. by using a weighted structure or driven pile, and is provided with buoyancy near the surface in order to keep the vertical steel pipe in tension. The end of tiie vertical steel pipe located toward the surface is connected to the surface vessel by a compliant flexible pipe.

Another riser configuration is a compliant vertical access riser (CVAR), in which the riser extends initially vertically from the seabed, forms a gentle *S-bend" and then terminates at the surface platform or vessel again in near vertical orientation. This configuration is able to absorb substantial vertical motion at the platform or vessel yet usee very little additional pipe.

SUMMARY OF INVENTION

Aspects of the present invention are defined by the independent claims. Preferred but optional features are defined by the dependent claims.

An aspect of the present invention may relate to a riser system, which may comprise a riser to be secured between a floating body and a subsea location. The riser may comprise a composite material formed of at least a matrix and one or more reinforcing elements embedded within the matrix.

In use, the riser may comprise or define a lower portion extending from the subsea location. The riser may comprise or define an upper portion extending from the: floating body, in use. The riser may comprise or define a bend or elbow between the lower and upper portions.

The lower portion may be configured to be substantially vertical, in use. The upper portion may be or comprise a substantially non-vertical portion. The upper portion may be configured to at least partially or wholly extend obliquely Or substantially perpendicularly relative to the iower portion and/or in a horizontal or lateral direction. The bend or elbow may be curved. The riser may take the form of an inverted catenary. The upper and/or Iower portions may be substantially linear, in use.

The bend or elbow may be pre-formed. The composite material at the bend or elbow may be arranged or configured to form the elbow or bend and/or permit, facilitate or promote bending, e.g. bending in a predetermined manner. The composite material in the bend or elbow may be arranged or configured differently to the composite material in at least part or all of the upper and/or Iower portions. For example, the composite material at the bend or elbow may comprise an orientation or orientation profile, length, and/or density of reinforcing elements, and/or a layup, that is different to that of the upper and/or Iower portions and/or forms, permits, facilitates or promotes a bend or elbow or bending in a predetermined manner.

The Iower and/or upper portion may be arranged to be in tension. The riser system may be arranged such that the Iower portion is under greater tension than the upper portion.

The bend or elbow and/or at least part of the upper portion may be provided towards or near but under a surface of a body of water, e.g. upon which the floating body floats.

The riser system may comprise one or more weights and/or buoyancy elements attached to the riser. In particular, one or more or each of the buoyancy elements may be attached or attachable to or arranged to at least partially form or support the bend or elbow. The buoyancy elements may be collapsible. The buoyancy elements may comprise air lift bags or rigid buoyancy cans or a combination, which may flooded and dewatered to provide variable buoyancy. Solid foam buoyancy may also be used One or more or each of the buoyancy elements may be connected to the riser by one or more tethers, e.g. chains or designed to be clamped around the riser two half shells. The riser may comprise, be fitted with or configured to receive one or more collars or other supporting members. The one or more tethers may connect between the buoyancy element and the collar or other supporting member.

The buoyancy elements may be arranged to provide a total upthrust at least sufficient to keep the lower section of the riser in tension and resist the current drag loads.

At least one or each of the buoyancy elements may be variable buoyancy elements, e.g. the buoyancy elements may comprise selectively variable or changeable buoyancy. At least one or each of the buoyancy elements may be selectively switchable or reconfigurable between at least a non-buoyant or less buoyant state and a buoyant or more buoyant state. The upthrust provided by the buoyancy elements may be adjusted by injecting air. At least one or each of the buoyancy elements may be selectively switchable or reconfigurable between the non-buoyant or less buoyant state and the buoyant or more buoyant state by injecting air into one or more or each of the respective buoyancy elements, e.g. using a remotely operated vehicle (ROV).

The buoyancy elements may be provided or arranged to be provided below the surface of the body of water, e.g. towards or on a surface side or end of the riser but under the surface of the body of water, in use.

The riser may comprise a light weight riser or pipe, which may be near neutrally buoyant, e.g. by virtue of its low self weight, the addition of lightweight coating or a combination of both.

The riser or riser system may be configured to have a buoyancy below a threshold buoyancy in at least a non-buoyant or less buoyant configuration. The non- buoyant or less buoyant configuration may be a negatively buoyant (e.g. sinking) configuration, e.g. in water such as sea water or brine or fresh water. The non-buoyant or less buoyant configuration may comprise a configuration in which at least one or all of the buoyancy elements are in the non-buoyant or less buoyant (e.g. deflated or less inflated) state and/or the riser is at least partially or wholly filled with water, such as sea water, brine or fresh water.

The riser or riser system may be configured to have a buoyancy equal to or above a threshold buoyancy in at least a buoyant or more buoyant configuration. The buoyant or more buoyant configuration may be a positively buoyant (e.g. floatable) configuration, e.g. in water such as sea water or brine or fresh water. The buoyant or more buoyant configuration may comprise a configuration in which at least one or all of the buoyancy elements are in the buoyant or more buoyant (e.g. inflated) state and/or the riser is at least partially or wholly filled with gas, such as air, natural gas, gaseous hydrocarbons, and/or the like,

The riser may be attached or attachable to a foundation at the base to anchor the riser. The foundation may be or comprise a ballast weight, driven pile, suction pile or directly connected to a Xmas tree or other item of subsea equipment. The riser system may comprise or be connected or connectable to a subsea system such as a lower riser package, a blow-out preventer (BOP), connector, a valve system, other device for connecting to a well-head, and/or the like. The subsea system or lower riser package may be attached to or provided on, at or proximate a subsea end of. the riser or an end of the riser or riser system that is toward the seabed and/or away from the floating body, in use. At least some of the weight or ballast may be provided by the subsea system or lower riser package.

The riser system may be adapted such that the total weight of the riser system, e.g. the riser, the subsea system or lower riser package and the one or each of the weights and/or the buoyancy elements may be greater than the buoyancy of the riser system in the non-buoyant or less buoyant configuration. The buoyancy of the riser system in the buoyant or more buoyant configuration may be greater than the total weight of the riser system.

In the riser system of the present invention, the riser and/or the lower riser package may naturally and straightforwardly lift away from the wellhead, at least when in the buoyant or more buoyant configuration. This may be due to at least one of the configuration, compliance and/or buoyancy arrangements described above. This may provide a quick, safe and/or stable emergency disconnect.

The riser system may be deployed or deployable or configured or arranged to be deployed down current or downstream of the floating object, i.e. the floating object may be up-current or upstream of at least part or all of the riser system (e.g. the lower riser package or subsea system and/or the subsea location) in use. The bend or elbow may bend or be configured to bend in an up-current direction as it transitions toward the surface, in use. The upper section may extend or be configured to extend at least partially or wholly parallel with the current or tide direction, in use. In the above, downstream or down current and upstream or up current are used in with reference to flow of fluid in a body of water in which the riser system is submerged and/or on which the floating body floats, e.g. upstream or downstream in relation to tides or currents.

The riser or riser system may be deployed or deployable from an overboard chute of the floating object, e.g. to manage the loads and strains in the riser pipe to acceptable installation levels and prevent damage to the pipe and/or coatings. The riser or riser system may be deployed or deployable in an 'over the side' deployment from the floating object.

The floating body may comprise at least one of a vessel, a Floating Production Storage and Offloading (FPSO) vessel, a floating platform, a Tension Leg Platform (TLP), a SPAR platform and a semi-submersible platform. However, any floating body as would be selected or understood in the art to possibly be associated with a riser may be utilised with the riser system. The floating body may be a surface, or near surface, floating body..

The subsea location may be a seabed location.

The riser may be secured to a fluid port at the subsea location. The riser may be secured to a fluid port of a subsea wellhead arrangement or a fluid port of a subsea manifold.

The matrix may comprise a polymer material. The matrix may comprise a thermoplastic material and/or a thermoset material. The matrix may comprise at least one of a polyaryl ether ketone, a polyaryi ketone, a polyether ketone (PEK), a poiyether ether ketone (PEEK), a polycarbonate, a polymeric resin and an epoxy resin.

The reinforcing elements may comprise at least one of fibres, strands, filaments and nanotubes. The reinforcing elements may comprise at least one of polymeric elements, aramid elements, non-polymeric elements, carbon elements, glass elements and basalt elements.

The riser system may comprise one or more fibre optic strain sensors.

The riser system may be configured for use in intervention and/or downline applications. The riser system may be configured for short term installation, e.g. less than six months, e.g. three months or less, which may be under one month, e.g. one week or less.

The riser may be configured to bend at a predetermined axial position or over a predetermined axial portion, e.g. at the bend or elbow. For example, the riser may be configured to have a reduced bending stiffness at a predetermined axial position, e.g. at the bend or elbow.

The riser may be configured to bend in a predetermined plane, which may comprise or be located at the bend or elbow. For example, the riser may be configured to have a reduced stiffness in a predetermined plane.

The riser may be configured to withstand a predetermined degree of bending, for example, bending at a predetermined axial position or over a predetermined axial portion, such as at the elbow or bend, and/or in a predetermined plane.

Such a riser may therefore be optimised to facilitate and withstand bending in localised regions, such as the bend or elbow. The other regions of the riser, such as the lower or upper portions, may only be designed to withstand reduced or zero bending stresses.

The riser may comprise a pipe having a pipe wail comprising the composite materiai, wherein the pipe wall may comprise or define a local variation in construction to provide a local variation in a property of the pipe, e.g. at the bend or elbow. The local variation in construction may comprise :at least one of a circumferential variation, a radial variation and/or an axial variation in the riser material and/or the pipe geometry.

The local variation in construction may comprise a local variation in the composite material.

The local variation in construction may comprise a variation in the matrix material. The local variation in construction may comprise a variation in a material property of the matrix material such as the strength, stiffness, Young's modulus, density, thermal expansion coefficient, thermal conductivity, or the like.

The local variation in construction may comprise a variation in the reinforcing elements. The local variation in construction may comprise a variation in a material property of the reinforcing elements such as the strength, stiffness, Young's modulus, density, distribution, configuration, orientation, pre-stress, thermal expansion coefficient, thermal conductivity or the like. The local variation in construction may comprise a variation in an alignment angle of the reinforcing elements within the composite material, In such an arrangement the alignment angle of the reinforcing elements may be defined relative to the longitudinal axis of the pipe. For example, an element provided at a 0 degree alignment angle will run entirely longitudinally of the pipe, and an element provided at a 90 degree alignment angle will run entirely circumferentiaily of the pipe, with elements at intermediate alignment angles running both circumferentiaily and longitudinally of the pipe, for example in a spiral or helical pattern.

The local variation in the alignment angle may include elements having an alignment angle of between, for example, 0 and 90 degrees, between 0 and 45 degrees or between 0 and 20 degrees.

At least one portion of the pipe wall, which may be associated with the elbow or bend, may comprise a local variation in reinforcing element pre-stress. In this arrangement the reinforcing element pre-stress may be considered to be a pre-stress, such as a tensile pre-stress and/or compressive pre-stress applied to a reinforcing element during manufacture of the pipe, and which pre-stress may be at least partially or residually retained within the manufactured pipe. A local variation in reinforcing element pre-stress may permit a desired characteristic of the pipe to be achieved, such as the bend or elbow. This may assist to position or manipulate the pipe, for example during installation, retrieval, coiling or the like. Further, this local variation in reinforcing element pre-stress may assist to shift a neutral position of strain within the pipe wall, which- may assist to provide more level strain distribution when the pipe is in use, and/or for example is stored, such as in a coiled or bent configuration.

An aspect of the present invention may relate to a method of forming a riser of a riser system according to one of the above aspects, the method comprising:

forming a fluid conduit from a composite material formed of at least a thermoplastic matrix and one or more reinforcing elements embedded within the matrix; and

forming the fluid conduit so as to provide a lower section configured to be substantially linear in use, an upper section angled obliquely to the lower section and an elbow or bend between the first and second portions.

An aspect of the present invention may relate to a method of using, installing or deploying a riser system according to at least one of the above aspects.

The method may comprise providing the riser system in the non-buoyant or less-buoyant configuration.

The method may comprise deploying the riser system from a floating object so that a lower portion extends substantially vertically and/or an upper portion extends obliquely to the lower portion and/or a bend or elbow is provided between the lower portion and the upper portion.

The method may comprise connecting the riser to a subsea structure.

The method may comprise reconfiguring the riser system into the buoyant or more-buoyant configuration.

The method may comprise flowing material in the riser.

An aspect of the present invention may relate to a riser system and/or may comprise a riser to be secured between a floating body and a subsea location. The riser may comprise a composite material formed of at least a matrix and one or more reinforcing elements embedded within the matrix.

The riser may comprise a lower end section. At least part of the iower end section may be located or locatable at the subsea location. The lower end section may be located or locatable on the seabed, in use. The Iower end section may be configured to extend substantially horizontally, e.g. along the seabed or sea floor, in use. The Iower end section may be connected or connectable to a subsea apparatus or system, such as a wellhead or tree arrangement.

The riser may comprise or define a Iower portion, which may extend from the subsea location. The Iower portion may be configured to be substantially vertical, in use. The iower portion may be or comprise a freestanding vertical section. The Iower ! end section may be connected or connectable to, integral with or in communication with the lower portion.

The lower end section may be connected to the lower portion via a bend or elbow, which may be or comprise a preformed or predetermined bend or elbow. For example, the bend or elbow may be pre-shaped into a bend or the materials or construction of the riser at the bend or elbow may be configured to form a bend in use. The bend or elbow may be connected or connectable to, integral with or in communication with the low portion and/or the lower end section.

The composite material at the bend or elbow may be arranged or configured to define, facilitate or promote the bend or elbow or to bend in a predetermined manner. The composite material at the bend or elbow may be arranged or configured differently to the composite material in at least part or all of the upper and/or lower portions. For example, the composite material at the bend or elbow may comprise an orientation, length, and/or density of reinforcing elements, and/or a layup, that is different to that of the lower end part and/or the lower portion. The elbow or bend may comprise a local variation in construction, which may comprise one or more features relating to the local variation in construction described above in relation to another aspect.

The lower portion may be connected to an upper portion. The upper portion may be or comprise a non-linear portion. The upper portion may comprise at least one, e.g. two or more points of inflexion. The upper portion may comprise at least one part that is untensioned and/or in compression, in use. At least an upper part of the upper portion may be under tension, in use. At least a lower or intermediate part of the upper portion may be under compression, in use. The upper portion may comprise one or a plurality of transitions between parts under tension and parts under compression.

The riser may comprise only a single pipe and/or substantially only a single type of pipe, such as a composite pipe. For example, the lower end part, the lower portion and/or the upper portion of the riser may comprise a single pipe or substantially a single type of type, such as a composite pipe.

The riser system may comprise one or more weights and/or buoyancy elements attached to the riser. In particular, one or more or each of the buoyancy elements may be attached at or proximate a transition between the lower portion and the upper portion.

The buoyancy elements may comprise air lift modules, such as open-ended buoyancy units. One or more or each of the buoyancy elements may be connected to the riser by one or more tethers, e.g. chains or clamped around the riser pipe in half shells. The riser may comprise, be fitted with or configured to receive one or more collars or other supporting members. The one or more tethers may connect between the buoyancy element and the collar or other supporting member.

At least one of the buoyancy elements may comprise a can, such as an air can. At least one of the buoyancy elements may be rigid. At least one of the buoyancy elements may be collapsible. At least one or each of the buoyancy elements may be formed from aramid or carbon fibre, e.g. aramid or carbon fibres in a matrix, such as a polymeric or resin matrix. In this way, weight and efficiency may be significantly improved, drag loading minimised and thereby riser response improved.

A plurality of the buoyancy elements may be configured to be located or distributed around the circumference of the riser. The buoyancy elements may comprise segmented buoyancy elements. The buoyancy elements may be configured to be assembled or arranged together in order to encircle or extend around the circumference of the riser. The buoyancy elements may be fixable or lockabie in position around the riser, e.g. by using one or more bands that are fitted or fittabie around the buoyancy elements, and/or by locking the buoyancy elements together and/or the like.

The riser may comprise one or more, e.g. one or more pairs of, limiters. The one or more limiters may be configured to engage at least one or more of the buoyancy elements. The one or more limiters may be configured to limit or prevent movement of the one or more buoyancy elements longitudinally along the riser, e.g. past the limiter. The at least one limiter may comprise a reaction surface, flange, collar, thickened or radially projecting wall section of the riser and/or one or more attachment mechanisms such as threaded or interference fit portions to which a collar or flange may be attached or attachable. The buoyancy elements may be provided or providable between the limiters of at least one of the pairs of limiters.

The lower portion may be under tension, in use. The tension in the lower portion may be at least partially provided by the buoyancy elements. The buoyancy may be configured to keep the lower portion substantially vertical. The buoyancy may be configured to support the lower portion. The lower portion may be or comprise a freestanding vertical section, which may be supported by the buoyancy.

The riser may be anchored at the subsea location, e.g. using a pile, anchor, weighted anchor, and/or the like. The weights and/or anchoring may be provided at, proximate or adjacent the bend or elbow. The upper portion may be provided at or near a surface, e.g. upon which the floating body floats.

The riser may be or comprise a compliant vertical riser (CVAR) riser or riser system. The riser system may take the arrangement of or be configured or operable as a single line offset riser (SLOR).

The floating body may comprise at least one of a vessel, a Floating Production Storage and Offloading (FPSO) vessel, a floating platform, a Tension Leg Platform (TLP), a SPAR platform and a semi-submersible platform. However, any floating body as would be selected or understood in the art to possibly be associate with a riser may be utilised with the riser system.

The floating body may be a surface or near surface floating body.

The subsea location may be a seabed location.

The matrix may comprise a polymer material. The matrix may comprise a thermoplastic material and/or a thermoset material. The matrix may comprise at least one of a polyaryl ether ketone, a polyaryl ketone, a polyether ketone (PEK), a polyether ether ketone (PEEK), a polycarbonate, a polymeric resin and an epoxy resin.

The riser system may comprise one or more fibre optic strain sensors.

An aspect of the present invention may relate to a method of forming a riser of a riser system according to the above aspect, the method comprising:

forming the fluid conduit so as to provide a lower end section connected to a lower portion via an bend or elbow such that the resulting riser has a pre-formed bend or elbow.

The lower portion may be substantially linear in use. The method may comprise attaching one or more buoyancy elements to an upper or top part of the lower portion of the riser. The method may comprise forming an upper portion of the riser, which may extend from the lower portion. The upper portion may be configured to adopt at least one, e.g. two or more points of inflexion and/or transition between one or more less tensioned or compressed and more tensioned regions, in use.

The method may comprise forming or providing a pre-formed bend or elbow in the composite riser at a subsea, e.g. seabed, location. The method may comprise anchoring the bend or elbow at the subsea or seabed location.

The method may comprise applying one or more buoyancy elements to an upper or top section of a lower portion of the composite riser, which may extend from the bend or elbow, e.g. in order to arrange the lower portion in a vertical and/or freestanding configuration and/or put the lower portion under tension.

The method may comprise flowing material in the riser.

According to an aspect of the present invention is a buoyancy system for attaching to a riser, the buoyancy system comprising a plurality of rigid hollow elements.

A plurality of the buoyancy elements may be configured to be located or distributed around the circumference of the riser. The buoyancy elements may comprise segmented buoyancy elements. The buoyancy elements may be configured to be assembled or arranged together in order to encircle or extend around the circumference of the riser. The buoyancy elements may be fixabie or lockable in position around the riser, e.g. by using one or more bands that are fitted or fittable around the buoyancy elements, and/or by locking the buoyancy elements together and/or the like.

The buoyancy system may be comprised in or usable with the riser systems of any of the above aspects and/or in the methods of any of the above aspects.

It should be understood that the individual features and/or combinations of features defined above in accordance with any aspect of the present invention or below in relation to any specific embodiment of the invention may be utilised, either severably and individually, alone or in combination with any other defined feature, in any other aspect or embodiment of the invention. Furthermore, the present invention is intended to cover apparatus configured to perform any feature described herein in relation to a method and/or a method of using or producing, deploying, using or manufacturing any apparatus feature described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of non-limiting example only with reference to the accompanying drawings of which:

Figure 1 is a schematic view of a riser system in an uninstalled configuration;

Figure 2 is a flowchart illustrating a method of installing the riser of Figure 1;

Figure 3 is a schematic view of the riser system of Figure 1 in a connected or operational configuration;

Figure 4 is a schematic view of the riser system of Figure 1 in an emergency disconnected configuration;

Figure 5 is a schematic showing another riser system;

Figure 6 is an exploded schematic of a buoyancy arrangement for use with the riser system of Figure 5;

Figure 7 shows a limiter for locating the buoyancy of Figure 6 in place on a riser; and

Figure 8 shows an arrangement for providing additional buoyancy of the type shown in Figure 6..

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 shows a riser system 5 comprising a composite riser 10 being deployed using an overboard chute 15 from a vessel 20 floating on the surface 25 of the sea 30. One end 35 of the riser 10 is retained on the vessel whilst a lower riser package 40 is attached to another end 45 of the riser 10.

The riser 10 is provided with a plurality of buoyancy elements 50, which in a deployment configuration of the riser system, are in the form of deflated open ended buoyancy units. Each buoyancy element 50 is fixed to a predetermined portion 55 of the riser 10 by a chain 60 extending between the buoyancy element 50 and a collar 65 that is affixed to the pipe 10 at the predetermined portion 55. The buoyancies of the riser 10 and the buoyancy elements 50 are selected with regard to the weight of the lower riser package 40, such that, when the buoyancy elements 50 are deflated and the riser 10 is filled with sea water, the riser system 5 has a negative buoyancy, i.e. it sinks. This may require extra weight to be added to the lower riser package 40 if required in order to obtain the correct buoyancy characteristics.

The deployment of the riser 10 is described in relation to Figure 2. In step 105, the riser 10 with the buoyancy elements 50 deflated is deployed downstream or down current 67 of the vessel 20 using the overboard chute 15. The lower riser package 40 acts as ballast, sinking towards the seabed 70 and pulling the riser 10 down with it.

Once the lower riser package 40 is located at the required position on the seabed 70, it can be connected and suitably fixed in position, e.g. using a remotely operated vehicle (ROV) in step 110. Thereafter, the buoyancy elements 50 are inflated to the required inflation in step 115, e.g. using the ROV. The buoyancy provided by the buoyancy elements 50 is selected such that the riser system 10 has positive buoyancy (i.e. it applies a surface-ward or up-thrust) when the buoyancy elements 50 are inflated. The buoyancy can be selected by use of appropriate numbers, sizes and/or inflation amounts of the buoyancy elements 50. For example, the buoyancy elements 50 could be configured to provide a total up-thrust of over 10Te, such as around 15 Te, when inflated. However, it will be appreciated that the amount of up-thrust required may differ depending on the application, the length of riser 10 and so on. The buoyancy elements 50 act to support a lower portion 75 of the riser 10 between the buoyancy elements 50 and the lower riser package 40 in a freestanding vertical or upright configuration.

Since the riser 10 is a composite riser, which is generally light weight relative to a corresponding steel riser, the operation of providing the required buoyancy may be made simpler and/or requires provision of less buoyancy elements.

As shown in Figure 3, once the buoyancy elements 50 have been inflated with the lower riser package 40 fixed at the subsea or seabed location 70, the riser system 5 is configured such that the buoyancy elements 50 are located toward or proximate but below the surface 25 of the sea 30. Sufficient additional riser 10 is deployed from the vessel 20 using the overboard chute 15 to allow the riser 10 to form an elbow 80 or bend under the action of the downstream current 67 and the buoyancy elements 50. The elbow 80 or bend is the part 55 of the riser 10 to which the buoyancy elements 50 are fixed and defines a directly curving transition between the substantially vertical arrangement of the lower portion 75 of the riser and an obliquely extending upper portion 85 of the riser 10 that extends between the elbow 80 and the vessel 20. It wilt be appreciated that the whole riser 10, i.e. the upper portion 85, the elbow 80 or bend and the lower portion 75 are all generally under tension, although the lower portion 75 may be under greater tension than the upper portion 85. Hie riser 10 effectively forms an inverted catenary, with the obliquely / horizontally extending upper portion of the riser 10 extending from the vessel 20 and being located near the surface 25, with the vertically extending lower portion 75 being connected to the subsea or sea bed location 70 via the lower riser package 40. In this way, the riser system 5 forms a free standing compliant riser.

However, since the buoyancy elements 50 largely support and tension the lower portion 75 of the riser 10 and the obliquely or horizontally extending upper portion 85 of the riser 1Q is coupled to the vessel 20, the tension and/or bending at the overboard chute 15 and on the deck of the vessel 20 may be advantageously reduced or minimised.

As described above, the elbow 80 or bend in the riser 10 can be provided by suitable provision of buoyancy elements 50 (e.g. using buoyancy elements 50 having different buoyancy in order to control the curve angle of the elbow 80 or bend, for example), along with the amount of riser 10 deployed and/or the use of the current or tide 67, i.e. the vessel 20 is positioned up-current of the lower riser package 40.

However, optionally, the properties and/or construction of the composite riser 10 can be selected in order to at least partially form or facilitate the elbow 80 or bend. For example, the properties may comprise the layup of the composite materials, the relative orientation of fibres, the average fibre length, the fibre or matrix density and so on, which can be suitably selected in order to provide, or promote formation of, the bend 80 or elbow at the required or predetermined position 55. it will be appreciated that this may comprise providing different properties or construction of the riser 10 for the bend 80 or elbow to that for at least part or all of the upper 75 and/or lower 80 riser portions.

In this example, the riser 10 is formed from a composite material comprising carbon fibre reinforcing elements (not shown) embedded within a matrix of potyether ether ketone (PEEK). The composite material of the riser 10 comprises a plurality of axially oriented carbon fibre reinforcing elements. As a result of this composite structure, the particular riser 10 shown in Figures 1 and 3 may permit large axial or bending strains, for example, axial or bending strains of up to 2% or more. This compares with typical maximum permissible axial or bending strains of a steel riser which may be in the region of approximately 0.1 %. Thus, the composite riser 10 offers significantly more compliance by virtue of its material properties alone compared with a conventional steel riser. Accordingly, the material properties of the riser' 10 compensate for the heave motion of the floating body relative to the fixed lower riser package 40, thus allowing attachment of the riser 10 between the vessel 20 and the lower riser package 40 without the need for any active heave compensation mechanisms such as hydraulic rams or the like. Furthermore, the arrangement comprising the bend or elbow 80 and the upper portion 85 provides additional give or compensation for heave motions of the vessel 20, at least relative to a riser system that is substantially vertical.

This arrangement results in surplus riser 10 being located at or near the surface

25, which has traditionally been considered unfavourable. However, for short term or temporary applications such as well intervention, this is less of a problem. Furthermore, the above configuration allows for a particularly beneficial emergency disconnect operation, as shown in Figure 4.

in this case, when it is necessary to disconnect the riser 10 quickly, e.g. in an emergency situation, the riser configuration and buoyancy arrangement described above acts to automatically pull the riser 10 and the lower riser package 40 away from the subsea location 70 as soon as the lower riser package 40 is disconnected. Particularly, since the riser system 5 has positive buoyancy in use with the buoyancy elements 50 inflated, the buoyancy elements 50 located below the surface 25 rise towards the surface 25, pulling the lower portion 75 of the riser 10 and the lower riser package 40 away from the sea bed 70. The naturally higher flexibility and compliance afforded by the composite riser 10 relative to correspondingly rated steel risers and the riser spatial arrangement described above provides the necessary compliance for the riser 10 to automatically lift a suitable distance away from the seabed 70 during the emergency release, particularly when the properties/construction of the riser 10 at the elbow 80 or bend are suitably selected.

Another riser configuration is shown in Figure 5. This shows a riser system 205 comprising a riser 210 that is substantially entirely formed from a composite material (except for any connectors or other components, for example, that may be mounted on the riser 210). In this way, a single pipe or pipe type is used throughout the riser 210, The riser 210 is configured as, or similar to, a single line offset riser (SLOR) but without the extensive vertical steel pipe section used in traditional SLOR systems.

in particular, the riser 210 comprises a lower end section 215 that extends generally horizontally along a sea bed 220, e.g. from a tree arrangement or wellhead 225, to an anchoring location 230. The riser 210 can be anchored at the anchoring location 230 by any suitable anchoring means known in the art, such as piling, weighted anchors, seabed engaging anchors and/or the like. The riser 210 is preformed with an elbow 235 or bend which substantially transitions through an angle between 60° and 120° and is located at the anchor location 230, e.g. on or near the sea bed 220.

From the bend or elbow 235, the riser extends generally vertically to form a tensioned freestanding vertical section 240 that is supported by a buoyancy system 245 at the top of the vertical section 240. The buoyancy system 245 comprises one or more open ended buoyancy units suitably attached to the riser, e.g. by using a collar and chain arrangement as described above or alternatively, the buoyancy units can be designed so to be clamped around the riser, e.g. by being provided in two half shells.

A particularly beneficial buoyancy arrangement is shown in Figures 6 to 8. Figure 6 shows a segmented buoyancy system 305 comprising a pair or rigid containers 310a, 310b in the form of two hollow half shells. Each container 310a, 310b is shaped so as to define a recess 315a, 315b. The containers 310a, 310b are configured such that the recessed surface of each container 310a, 310b face together such that the recesses 315a, 315b together define a through passage 320 into which the riser 210 is received in use. in this way, the containers 310a, 310b can be fitted around the riser 210 in use, so that the pair of containers 310a, 310b together encircle the riser 210. Each container 310a, 310b is rigid and may be formed from carbon fibres embedded in a resin matrix. The containers 310a, 310b are fixab!e together in position around the riser 210, e.g. by fixing one or more bands 325 around the containers 310a, 310b, although other mechanisms for locking the containers 310a, 310b in position would be apparent to one skilled in the art.

The riser 210 comprises a pair of thickened pipe sections 330a, 330b, the containers 310a, 310b being located between the thickened pipe sections 330a, 330b. The thickened pipe sections 330a, 330b are configured to have an outer diameter that is larger than the diameter of the passage 320. In this way, motion of the buoyancy system 305 along the riser 210 can be limited by the thickened sections 330a, 330b.

One of the thickened sections 330a is shown in detail in Figure 7. The other thickened section 330b is essentially the mirror image of the thickened section 330a. it wiil be appreciated that the buoyancy system 305 can engage the thickened sections 330a, 330b of the riser 210 directly or the thickened sections 330a, 330b can be used to mount a collar and/or flange 335 and the buoyancy system 305 engages or is fixed to the collar or flange 335. The buoyancy may. be increased by providing muitipie buoyancy systems 305 along the riser 210, as shown in Figure 8.

Although the buoyancy system 305 is shown as being formed from pairs of half shells, it will be appreciated that other arrangements or numbers of buoyancy elements or containers 310a, 310b could be used for each set. Similarly, although the buoyancy elements or containers 310a, 310b are shown as being connected together using bands 325, it will be appreciated that other arrangements for fixing the buoyancy elements or containers 310a, 310b together could be used. For example, the buoyancy elements or containers 310a, 310b could be hinged together at one side edge and lockable together at an opposite side edge.

From the buoyancy system 245, the riser 210 is configured to curve through two points of inflexion 250a, 250b to a vessel 255. In this way, from the portion of the riser 210 at the buoyancy system 245, the riser 210 goes through a less tenstoned, untensioned or compressed portion 260 before extending into a tensioned portion 265 as it approaches the vessel 255. In this way, the riser system 205 effectively comprises a compliant vertical access riser (C VAR) that is operable in a similar manner to a SLOR.

The provision of the buoyancy system 245 at the top of the vertical section 240 allows the an entirely composite freestanding vertical section 240 of the riser 210 to be used, in contrast to traditional SLOR systems that use a steel piped vertical section. Furthermore, due to the pre-formed elbow 235 or bend section and the above buoyancy system 245, composite pipe can be used for substantially the whole riser 210, minimising connections and strains that may otherwise result from steel pipe to composite pipe interfaces.

As in the embodiments described above in relation to Figures 1 to 4, the riser

210 in this example comprises a composite material formed of a matrix of polyether ether ketone (PEEK) and carbon fibre reinforcing elements (not shown) embedded within the PEEK matrix. The composite material of the riser 210 comprises a plurality of axially oriented carbon fibre reinforcing elements.

The preformed elbow 235 or bend can be formed by suitable shaping, forming or moulding of the riser pipe during production. Furthermore, the elbow 235 can be pre-formed or the riser pipe made suitable for bending at the predetermined location by forming the elbow 235 or bend portion of the riser pipe 210 with an appropriate composite material construction, e.g. using an appropriate layup, fibre orientation ratio or profile, average fibre iength, fibre density, matric material and/or the like, similar to the manner described above in relation to the embodiment of Figures 1 and 3.

One skilled in the art will understand that various other riser arrangements and spatial configurations are possible without departing from the scope of the present invention.

For example, although the specific examples or riser 10, 210 described above are formed from carbon fibre embedded In a PEEK matrix, it will be appreciated that other materials could be used to form the composite pipe. For example, the matrix may comprise other polymeric materials, such as a thermoplastic material and/or a thermoset material. Specific examples of possible matrix materials include at least one of a polyaryl ether ketone, a polyaryl ketone, a polyether ketone (PEK), a polyether ether ketone (PEEK), a polycarbonate, a polymeric resin and an epoxy resin. Similarly, the reinforcing elements could comprise at least one of fibres, strands, filaments and nanotubes, which may comprise at least one of polymeric elements, aramid elements, non-polymeric elements, carbon elements, glass elements and basalt elements.

In addition, although open ended buoyancy units are described above with reference to the buoyancy elements or system 50, 245, it will be appreciated that other buoyancy types could be used, such as enclosed buoyancy units, and/or the like.

Although in the above examples the buoyancy elements or system 50, 245 is inflated using an ROV, it will be appreciated that other inflation mechanisms such as inflation lines could be provided and/or divers used to inflate the buoyancy 50, 245.

As such, the above specific examples are given for illustration only and the scope of the invention is limited only by the claims.

Claims

1. A riser system comprising a riser to be secured between a floating body and a subsea iocation, the riser comprising a composite material formed of at least a matrix and one or more reinforcing elements embedded within the matrix;

the riser system being arranged such that, in use, the riser comprises or defines:

a lower portion extending from the subsea Iocation;

an upper portion extending from the floating body; and

a bend or elbow between the lower and upper portions.

2. The riser system of claim 1, comprising one or more buoyancy elements, wherein one or more or each of the buoyancy elements are attached to or arranged to form or support the bend or elbow.

3. The riser system of claim 2, wherein at least one or each of the buoyancy elements are variable buoyancy elements having selectively variable or changeable buoyancy.

4. The riser system of claim 3, wherein at least one or each of the buoyancy elements are selectively switchable or reconfigurable between at least a non-buoyant or less buoyant state and a buoyant or more buoyant state by inflating and/or deflating one or more or each of the buoyancy elements.

5. The riser according to claim 3 or claim 4, wherein the riser or riser system is configured to have a negatively buoyant configuration in at least a non-buoyant or less buoyant configuration.

6; The riser according to any preceding claim, wherein the riser or riser system may be configured to have positive buoyancy in at least a buoyant or more buoyant configuration.

7. The riser of claim 5 or claim 6, wherein buoyant or more buoyant configuration is a configuration in which the buoyancy elements are inflated and/or the non-buoyant or less buoyant configuration is a configuration in which the buoyancy elements are deflated or less inflated than when in the buoyant or more buoyant configuration.

8. The riser system according to any preceding claim, wherein the lower portion is configured to be substantially vertical, in use and the upper portion is configured to at least partially extend obliquely or substantially perpendicularly relative to the lower portion and/or in a horizontal or lateral direction.

9. The riser according to any preceding claim, wherein the bend or elbow and/or at least part of the upper portion is/are provided towards or near but under a surface of a body of water upon which the floating body floats.

10. The riser system according to any preceding claim, wherein the riser takes the form of an inverted catenary.

11. The riser according to any preceding claim, wherein the bend or elbow is preformed.

12. The riser according to claim 11, wherein the composite material at the bend or elbow is arranged or configured to form the elbow or bend and/or permit, facilitate or promote bending in a predetermined manner.

13. A method of forming a riser of a riser system according to any preceding claim, the method comprising:

14. A method of using, installing or deploying a riser system according to any of claims 1 to 12, the method comprising: deploying the riser system from a floating object so that a lower portion extends substantially vertically and/or an upper portion extends obliquely to the lower portion and/or a bend or elbow is provided between the lower portion and the upper portion; connecting the riser to a subsea structure.

15. The method according to claim 14, wherein the riser system is deployed when in a non-buoyant or less-buoyant configuration and the method comprises reconfiguring the riser system into the buoyant or more-buoyant configuration after the riser is connected to the subsea structure.

16. A riser system comprising a riser to be secured between a floating body and a subsea location and one or more buoyancy elements, the riser comprising a composite material formed of at least a matrix and one or more reinforcing elements embedded within the matrix; wherein

the riser comprises:

a lower end section located or locatable on the seabed, in use; and a lower portion that extends from the subsea location, wherein the lower portion is connected to the lower end section via a preformed or predetermined bend or elbow, wherein

at least one of the buoyancy elements is configured to support the lower portion.

17. The riser system of claim 16, wherein the buoyancy elements are configured to support the lower portion so as to be substantially vertical, in use.

18. The riser according to claim 17, wherein the lower portion comprises a freestanding vertical section supported by the buoyancy.

19. The riser according to any of claims 16 to 18, wherein the riser comprises only a single pipe and/or substantially only a single type of pipe.

20. The riser system of any of claims 16 to 19, wherein the bend or elbow comprises a preformed or predetermined bend or elbow.

21. The riser of claim 20, wherein the bend or elbow is pre-shaped into a bend or the materials or construction of the riser at the bend or elbow are configured to form a bend in use.

22. The riser of any of claims 16 to 21, wherein the lower portion is connected to a non-linear upper portion.

23. The riser of claim 22, wherein the upper portion comprises two or more points of inflexion.

24. The riser of claim 23, wherein the upper portion may comprise at least one part that is untensioned and/or in compression, in use and at least one other part that is under tension, in use.

25. The riser according to any of claims 16 to 24, wherein the riser is or comprises a compliant vertical riser (CVAR) riser or riser system.

26. The riser according to any of claims 16 to 25, wherein the riser system is configured to take the arrangement of or be configured or operable as a single line offset riser (SLOR).

27. The riser system according to any of claim 16 to 26, wherein the buoyancy elements comprise rigid buoyancy elements.

28. The riser system according to any of claims 16 to 27, wherein a plurality of the buoyancy elements that are configured to be located or distributed and/or connectable together around the circumference of the riser.

29. The riser system according to claim 28, wherein the riser is provided with one or more limiters for limiting the movement of the buoyancy along the riser.

30. The riser system according to claim 29, wherein the limiters comprise at least one of. a reaction surface, flange, collar, thickened or radially extending wall section of the riser and/or attachment mechanisms such as threaded or interference fit portions to which a collar or flange are attached or attachable.

31 A method of forming a riser of a riser system according to any of claims 16 to 30, the method comprising:

32. The method of claim 31, comprising providing one or more buoyancy elements on an upper or top part of the lower portion of the riser.

33. A method of using, installing or deploying a riser system according to any of claims 16 to 30, the method comprising forming or providing a pre-formed bend or elbow in the composite riser at a subsea location.

34. The method of claim 33 comprising anchoring the bend or elbow at the subsea or seabed location.

35. The method of claim 33 or 34, comprising applying one or more buoyancy elements to an upper or top section of a lower portion of the composite riser in order to arrange the lower portion in a vertical and/or freestanding configuration and/or put the lower portion under tension.

36. A buoyancy system for attaching to a riser, the buoyancy system comprising a plurality of rigid hollow elements, the hollow elements being iocatable or fixable together around the riser in order to define a channel for receiving the riser therein.

37. A riser system substantially as shown in the Figures and described herein in relation to the drawings.

38. A buoyancy system as as shown in the Figures and described herein in relation to the drawings.