WO2012065218A1

WO2012065218A1 - A segmented riser bundle

Info

Publication number: WO2012065218A1
Application number: PCT/AU2011/001477
Authority: WO
Inventors: Emmanuel René Jean-Pierre FONTAINE; Andrew Alan Kilmer; Hayden Marcollo
Original assignee: Amog Technologies Pty Ltd
Priority date: 2010-11-16
Filing date: 2011-11-15
Publication date: 2012-05-24

Abstract

A riser module (10) including an outer tubular (30) internally carrying two or more internal tubulars (20). The module (10) further includes a decouplable coupling and sealing arrangement at each end of the module wherein an end of the outer tubular (30a) is couplable to the other end of a like outer tubular (30b) of an adjacent module (10b) for serial connection of a plurality of modules to form a riser, and each of the two or more internal tubulars (20a) is able to cooperate with like internal tubulars (20b) of adjacent modules to define a respective sealed flow path through the coupled modules (10). In the preferred form the outer tubular (30) constitutes a load bearing structure and the coupling and sealing arrangement of each module (10a) is configured to permit axial movement between each of the two or more internal tubulars (20a) and respective cooperating internal tubulars (20b) in an adjacent module (10b).

Description

A segmented riser bundle

Field of the invention

The invention relates to risers for hydrocarbon production.

Background of the invention

'Hydrocarbon production' refers to the extraction of hydrocarbon, eg oil and gas, from naturally occurring deposits. These deposits typically occur deep within the earth and often also deep underwater.

A riser is a tubular structure for conveying the hydrocarbon from structure on the seabed to structure at or adjacent the sea surface, eg for conveying the hydrocarbon to a floating production storage and offloading (FPSO) vessel. A 'riser bundle' includes multiple flow paths for conveying hydrocarbon from multiple production wells.

Standard existing deepwater drilling risers feature a central marine riser, which can be of 13 3/8" nominal diameter, or 21" nominal diameter or other such diameters. These may have a drill string of about 5" which have a drill bit on the end and can rotate. The marine riser can have outer pipes which are known as kill and choke pressure lines and can be up to 6" diameter for the purposes of controlling well operations. These kill and choke lines do not have hydrocarbons in them. The kill and choke lines have to take into account the dynamic and static angles of the marine riser and for marine risers that contain flex joints (particularly deep water risers) these lines are sometimes wound in coils to accommodate the flexibility. These risers do not have multiple paths and do not normally produce hydrocarbons.

Risers are typically constructed in long horizontal lengths prior to installation in the upright position. Moving a typical riser is an expensive and time consuming operation. As such typical risers are considered 'semi-permanent': it would be unusual to relocate a typical riser. An easily relocatable riser system would be desirable in the context of early field testing so the riser could be relocated until a desirable location is found. A relocatable riser system would also be desirable in the context of oil fields having low recoverable total oil reserves, in which case the riser could be relocated from time to time to extract the most readily available remaining oil.

Relocatablility would also be advantageous in environments prone to hurricane/cyclonic conditions in that the riser could be moved to avoid adverse weather conditions.

US patent no. 4,332,509 describes a riser system in which sections carrying conduits are connected end to end to form a column and then flow lines for conveying hydrocarbons passed through the conduits of the column of assembled sections.

Figure 1 illustrates an existing segmented riser for a drilling rig. It includes a rotating drill pipe 101 operating inside a marine drilling riser pipe 103. During drilling operations, drilling fluids and mud is circulated down the centre of the rotating drill pipe to the rotating drill bit at the bottom and returned up the inside of the marine drilling riser pipe in the annulus between the marine drilling riser pipe 103 and the drill pipe 101. The drilling riser is installable from a surface host in segments with connectors 104 between the segments that are connected together at the surface host during the deployment process and disconnected at the surface host during the retrieval process. Kill and choke lines 102 are located on the external part of the system for the purposes of providing well control via pressurised control type fluids. The kill and choke lines have seals at the main connector locations to allow for pressure integrity.

It is not admitted that any of the information in this specification is common general knowledge, or that the person skilled in the art could be reasonably expected to have ascertained or understood it, regarded it as relevant or combined it in anyway at the priority date. Summary of the invention

One aspect of the invention provides a riser module including an outer tubular internally carrying two or. more internal tubulars; a decouplable coupling and sealing arrangement at each end of the module wherein an end of the outer tubular is couplable to the other end of a like outer tubular of an adjacent module for serial connection of a plurality of modules to form a riser, and each of the two or more internal tubulars is able to cooperate with like internal tubulars of adjacent modules to define a respective sealed flow path through the coupled modules;

Being decouplable permits retrieval and reuse of preferred forms of the module.

Preferably a further tubular internally carries the two or more tubulars.

Each of the two or more tubulars may be embraced by an insulating sleeve within the further tubular, preferably each of the two or more tubulars is respectively embraced by an insulating sleeve. The insulating sleeve(s) may be formed of wet insulation.

Optionally the coupling and sealing arrangement includes an outward radial flange about each end of the further tubular, one of the flanges being rigidly coupled to the flange at the other end of the like tubular when the module is so coupled.

Preferably the module includes an elongate load bearing structure and the coupling and sealing arrangement is configured, when so coupled, to permit axial movement between each of the two or more internal tubulars and their respective cooperating internal tubulars in an adjacent module. The load bearing structure is preferably external to the two or more tubulars. T,he further tubular may constitute the elongate load bearing structure. The coupling and sealing arrangement seals connected outer tubulars to separate the internal and external environments of the module while allowing axial movement of the internal tubulars..

In preferred forms of the invention, each of the two or more internal tubulars is fixed relative to the outer tubular at a single axial location, most preferably a common axial location, to permit differential expansion between the two or more internal tubulars and the outer tubular. It is preferred that the single axial location(s) be at or adjacent a top end of the module whereby one end of the two or more tubulars is free to move relative to the outer tubular. This gives the inner tubulars the appearance of being suspended within the outer tubular. At least one spacing element spaced from the single axial location(s) to laterally restrain the two or more tubulars relative to the load bearing structure may be provided.

The module may include structure to mount one or more umbilicals for control or subsea power. In use umbilicals may be reeled out and attached to the side of the riser as segments of the riser are installed.

Another aspect of the invention provides a riser including a plurality of the modules connected end to end. At least one, and preferably a plurality, of the modules may have one or more floats. The buoyancy of the floats may vary as a function of the depth. Another aspect of the invention provides the riser when used to produce hydrocarbon, each of the two or more tubulars conveying the hydrocarbon.

Another aspect of the invention provides a method of producing hydrocarbon, the method including coupling the modules end to end to form a riser and conveying the hydrocarbon through each of the two or more tubulars.

Brief description of the drawings

Figure 1 is a vertical cross section view of a prior art segmented riser for a drilling rig; Figures 2, 3 and 4 are horizontal cross section views of a module in accordance with an embodiment of the invention;

Figure 5 illustrates longitudinally adjacent end portions of like modules prior to connection; Figure 6 illustrates the end portions of two longitudinally adjacent modules when coupled together;

Figure 7 schematically illustrates a riser in accordance with an embodiment of the invention in situ; and

Figure 8 is a schematic view showing the interconnection of end portions of two longitudinally adjacent internal tubulars.

Detailed description of the embodiments

Figures 2 to 6 show details of a module 10 in accordance with an embodiment of the invention. Figure 7 illustrates a production system 80 incorporating the module 10.

Each module 10 includes four parallel internal tubulars 20 for conveying hydrocarbon from four respective sources of hydrocarbon on the sea floor. The internal tubulars 20 are arranged in a square array. An outer tubular 30, carries the array of tubulars 20.

The internal tubulars 20 have a nominal diameter of 6" and are formed of X-65 grade carbon alloy steel. The material grade may be varied to suit differing internal flow pressures. The outer tubular has a nominal diameter of 21 ".

The produced hydrocarbon is typically warmer than the surrounding seawater. It is preferable to insulate the produced hydrocarbon from the seawater as excess cooling would lead to the hydrocarbon thickening and the formation of waxes. The outer tubular 30 serves to insulate the internal tubulars 20, and in this embodiment each internal tubular 20 is encased in an insulating sleeve 22 within the outer tubular to provide further insulation.

As will be described, the outer tubular 30 when in situ may define a dry sealed internal volume so that the internal tubulars 20, or more specifically the insulating sleeves 22, are exposed to air rather than water. In this case the insulating sleeves 22 may be formed of dry insulating material in the form of glass syntactic polyurethane foam (GSPU). However, it is preferred that the interior of the outer tubular 30 be flooded, in which case the insulating sleeves 22 would be formed of wet insulating material. Figure 3 shows a spacer 40 carried within the outer tubular 30. The spacer 40 is a disc shaped member which spans the interior of the outer tubular 30. The spacer 40 includes a square array of circular holes complementary to the internal tubulars 20 and insulating sleeves 22. The spacer 40 thus serves to laterally position the internal tubulars 20 within the outer tubular 30. Typically each module would include a plurality of spacers 40 along its length.

In embodiments in which the outer tubular 30 is to be flooded, the spacer 40 may be provided with flow apertures 44 to permit longitudinal flow of water through the module. In this embodiment, the spacer 40 includes four apertures 44 equally spaced about the member 40. Each aperture 44 is centrally positioned within a void space between, and outward from, a pair of apertures 42.

Differences in temperature between the produced hydrocarbon and the surrounding seawater lead to differential expansion of the internal tubulars 20 relative to the outer tubular 30. The internal tubulars 20 are not axially connected to the spacer 40 so as to permit axial sliding movement there between to accommodate this differential thermal expansion. It is also possible that the produced hydrocarbon within each respective tubular 20 might be at differing temperatures. This sliding fit arrangement also accommodates the differential expansion between each respective internal tubular 20. When modules are connected together to form a riser, the internal tubulars connect to like tubulars in adjacent modules to form internal conduits extending through the connected outer tubulars. The accommodation of differential thermal expansion between the inner conduits is also important in the case of the riser system requiring quick disconnection and circulation or flushing of the inner conduits with water to empty the hydrocarbons. This flushing is likely to occur one pipe at a time and result in the inner pipes being of different lengths.

As shown in figure 5 a mounting disc 60 spans the outer tubular 30 towards an upper end of module 10. The mounting disc 60 includes a square array of circular holes to accommodate the internal tubulars 20 and the insulating sleeves 22. The disc 60 is rigidly mounted to the outer tubular 30 and to each of the internal tubulars 20. The mounting disc 60 serves to fix the internal tubulars 20 relative to the outer tubular 30 at a common single axial location. As such, in this embodiment, the internal tubulars 20 are fixed adjacent the upper end of the module 10 and free to expand downwardly when heated by the produced hydrocarbon. Thus by suspending the internal tubulars 20, the tubulars 20 are kept in tension which serves to prevent buckling.

Each end of the module 10 includes a coupling and sealing arrangement 70a, 70b.

As further shown in figure 5, the lower end of each module terminates in the coupling and sealing arrangement 70a. An end of the outer tubular 30a is couplable to the other end of a like outer tubular 30b of an adjacent module 10b for serial connection of a plurality of modules to form a riser. Each of the two or more internal tubulars 20a is able to cooperate with like internal tubulars 20b of adjacent modules 30b to define a respective sealed flow path through the coupled modules 30a, 30b. The coupling and sealing arrangement 70a includes an outwardly projecting radial flange 78 encircling the lower end of the outer tubular 30a. The flange 78 carries a circular array of bolting apertures. The upper end of the module 10b carries a coupling and sealing arrangement 70b which includes a radial flange 79 extending outwardly about an upper end of the outer tubular 30b. The flange 79 includes a circular array of bolting apertures complementary to the bolting apertures of the flange 78. During installation the flanges are brought into abutment and bolts 77a are passed through the bolting apertures to cooperate with nuts 77b. Once the nuts 77b are tightened onto the bolts 77a the vertically adjacent modules 10a, 10b are rigidly connected.

As shown in figure 8, the coupling and sealing arrangement 70a further includes a stab-in connector 72 at the lower end of each tubular 20a. Each stab-in connector includes an end portion of the tubular 20a which is stepped down to a diameter smaller than the remainder of the tubular 20a. Each smaller diameter portion is receivable with an end 76 of the corresponding tubular 20b in the vertically adjacent module 10b. The smaller diameter portion of each stab-in connector 72 carries a pair of elastomeric seals in the form of O-rings in outward facing circumferential grooves. In use the O-rings 74 on internal tubulars 20a engage the cylindrical interior of the upper end of 76 of the corresponding internal tubular 10b to form a piston seal.

The elastomeric seals could be formed of Polyphenylene Sulfide (PPS) materials or PEEK materials which trade under the names of Rylon or Arlon or Teflon - Avalon and are able to cope with exposure to oil, gas, condensate hydrocarbon service, typical well production pressures and temperatures, and are resistant to explosive decompression as well as being resistant to H₂S and amine corrosion inhibitors.

The outer tubular 30 constitutes a secondary sealing arrangement to protect the marine environment from leaking hydrocarbon if one or more of internal tubulars 20, or one or more connections between tubulars 20, were to fail. As such preferred embodiments of the invention are properly regarded as dual containment systems. Alternatively production could be achieved using the path in between the outer tubular 30 and the inner tubulars 20, e.g. this path might convey produced gaseous hydrocarbon. In these circumstances, only a single containment system would exist.

This piston seal arrangement permits relative axial movement between each internal tubular 20 and its corresponding internal tubular in the adjacent module which would normally be vertically positioned. As a consequence, axial load is not transmitted via the internal tubulars 20 to like internal tubulars in vertically adjacent modules. The axial load is carried by the outer tubular 30. As such the outer tubular 30 constitutes an elongate load bearing member external to the internal tubulars 20 and is the primary load bearing member.

The modules may be fitted with floats to at least partly counteract their weight whereby to reduce the tension at the top of the riser. Figure 4 illustrates a portion of module 10 encased in a float in the form of tubular sleeve 50.

Figure 7 illustrates a hydrocarbon production system 80 incorporating a riser 1 , which includes eight modules 10, a well centre 81 , production line 82, a riser base 82A, an FPSO 84, a transfer line 85, and a transport vessel 86. In addition to the production line 82, other flow lines (not shown) including injection lines and hydraulic control lines connect the well centre 81 and the riser base 82A. The hydrocarbon production is made through the production line while the injection line is used to inject chemicals into the oil/gas. The control lines carry fluids from an umbilical to the well centre.

The well centre 81 and the riser base 82A at the lower end of the riser 1 are mounted on the seabed 83A. The line 82 fluidly connects the well centre 81 to the riser base 82A and inturn the riser 1.

The FPSO 84 sits at the water surface 83B and includes a moon pool 84A and derrick 84B. The derrick 84B suspends the riser 1 through the moon pool 84A.

As illustrated, within riser 1 , the modules 10 are serially connected end to end by their sealing and coupling arrangements 70. In operation, hydrocarbon produced at the well centre 81 is transferred to the riser 1 by the production line 82. The production line 82 communicates with one of the four flow paths defined by the riser 1 for conveying the hydrocarbon to the FPSO. It will be appreciated that the riser system 80 may include three further well centres (not shown), each communicating with a respective one of the three other flow paths within the riser 1. The produced hydrocarbon received from the riser 1 is temporarily stored aboard the FPSO. Periodically the transport vessel 86 will connect with the FPSO 84 via the transfer line 85 to receive a batch of produced hydrocarbon from the FPSO 84.

Other production systems are possible. By way of example, the upper end of the riser might be supported by a submerged buoyancy can and communicated with the FPSO by flexible lines between the can and the FPSO, rather than being directly connected to the FPSO as in figure 7. Preferably, the flexible lines between the can and FPSO can be disconnected and the FPSO can weathervane.

The described embodiments offer several advantages over prior art arrangements. The modular construction allows for rapid installation, whilst the releasable sealing and coupling arrangement 70 permits rapid disassembly, eg to move to another oil field. Each module is desirably a convenient length to be pulled aboard an installation vessel. A length of about 20 metres is thought to be desirable.

Additionally, rather than complete disassembly of the riser 1 , a lower end of the riser may be decoupled at a point adjacent to the seabed to permit transport of a plurality of assembled modules, eg a near complete riser 1 , to a new location. In a preferred mode of operation, adjacent modules 10 are decoupled adjacent to the surface whereby the FPSO can be moved to avoid inclement weather and then repositioned and reconnected to the in place modules to continue production. In the system 80, floats to provide buoyancy are installed over most of the modules 10. Vortex-Induced vibration suppression is also installed over the segments that are expected to have high velocity currents. The suppression may be weather-vaning fairings. Optionally the fairings may be installed as the riser is installed.

In certain geographical locations of the world, such as tropical cyclone or hurricane regions disconnectability is particularly desirable. In these situations, like a deep water drilling riser, the lower part of the riser system could be designed to be disconnectable at its base under emergency situations such as a drift off scenario or an equipment failure condition. For this purpose, the lower part of the riser may contain a riser flushing and circulation system to enable the hydrocarbons to be flushed out of each of the inner pipes. The upper part of the riser may be tensioned just like a deep water drilling riser system.

It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Claims

1. A riser module including an outer tubular internally carrying two or more internal tubulars; a decouplable coupling and sealing arrangement at each end of the module wherein an end of the outer tubular is couplable to the other end of a like outer tubular of an adjacent module for serial connection of a plurality of modules to form a riser, and each of the two or more internal tubulars is able to cooperate with like internal tubulars of adjacent modules to define a respective sealed flow path through the coupled modules.

2. The module of claim 1 wherein the outer tubular constitutes a load bearing structure and the coupling and sealing arrangement of each module is configured to permit axial movement between each of the two or more internal tubulars and respective cooperating internal tubulars in an adjacent module.

3. The module of claim 1 or 2 wherein each of the two or more internal tubulars is embraced by an insulating sleeve within the outer tubular.

4. The module of claim 3 wherein each of the two or more tubulars is respectively embraced by an insulating sleeve.

5. The module of claim 3 wherein the insulating sleeve(s) is formed of wet insulation.

6. The module of claims 2 wherein the decouplable coupling and sealing arrangement includes an outward radial flange about each end of the outer tubular, the radial flange of one outer tubular being rigidly couplable to the flange at one end of an adjacent outer tubular.

7. The module of claim 2 wherein each of the two or more internal tubulars is fixed relative to the outer tubular at a single axial location to permit axial differential expansion between the internal tubulars and the outer tubular.

8. The module of claim 7 wherein the two or more internal tubulars are fixed relative to the load bearing structure at a common single axial location.

9. The module of claim 7 or 8 wherein the single axial location(s) is at or adjacent a top end of the module whereby the two or more internal tubulars are suspended within the outer tubular. 0. The module of claim 9,

10 or 11 further including at least one spacing element spaced from the single axial location(s) to laterally restrain the two or more tubulars relative to the load bearing structure.

11. A riser including the two or more adjacent modules of claim 2 connected end to end.

12. The riser of claim 11 wherein a plurality of the modules each carry one or more floats and the buoyancy of the floats varies as a function of the depth.

13. The riser of claim 11 when used to produce hydrocarbon, each of the two or more tubulars conveying the hydrocarbon.

14. A method of producing hydrocarbon, the method including coupling modules of claim 1 or 2 together end to end to form a riser, and conveying the hydrocarbon through each of the two or more internal tubulars.

15. The method of claim 14 further including the steps of decoupling the modules; moving the modules to a different location or orientation; and recoupling the modules.