WO2009139636A1 - Assembly of flexible riser systems - Google Patents

Assembly of flexible riser systems Download PDF

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Publication number
WO2009139636A1
WO2009139636A1 PCT/NO2009/000155 NO2009000155W WO2009139636A1 WO 2009139636 A1 WO2009139636 A1 WO 2009139636A1 NO 2009000155 W NO2009000155 W NO 2009000155W WO 2009139636 A1 WO2009139636 A1 WO 2009139636A1
Authority
WO
WIPO (PCT)
Prior art keywords
chain
riser
seabed
risers
anchor
Prior art date
Application number
PCT/NO2009/000155
Other languages
French (fr)
Inventor
Loseth Svein
Original Assignee
Statoilhydro Asa
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Statoilhydro Asa filed Critical Statoilhydro Asa
Publication of WO2009139636A1 publication Critical patent/WO2009139636A1/en
Priority to DKPA201070078A priority Critical patent/DK201070078A/en

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Classifications

    • EFIXED CONSTRUCTIONS
    • E21EARTH OR ROCK DRILLING; MINING
    • E21BEARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B17/00Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
    • E21B17/01Risers
    • E21B17/015Non-vertical risers, e.g. articulated or catenary-type

Definitions

  • the present invention relates to flexible risers, cables and the like, and in particular to assembly of flexible riser, cables and the like from a sub-sea position to a position at the surface of the sea.
  • risers For transfer of fluids, such as oil and gas from a seabed level to a level at or near the sea surface, risers are used. If fluids are to be transferred between a level at sea bottom and a floating installation or another installation having a variable position, risers are used in the form of flexible pipes. There are many solutions available how one or more flexible pipes can be arranged from a sea bottom to position at the surface so that the installation can be made conveniently, the length of the flexible risers not being of an excessive length and the load on the risers is limited and the operating lifetime for the risers are as long as possible.
  • API RP 17B The American Petroleum Institute has published a recommended practice for assembling risers, API RP 17B, where the most common forms of assembling, such as lazy wave and steep wave, are described.
  • the tension/tensile anchoring ensures that the flexible pipe is not bended more than what minimum bending radius allows.
  • each riser comprises an upper part extending as a chain line downward and away from a position at the sea surface, an intermediate part with a length interval with buoyancy devices arranged on or attached to the riser, in order to provide a positive buoyancy in said length interval, and the intermediate part assuming a concave form directed towards the seabed, and a lower part extending as a chain line further down and away from the position at the sea surface to a seabed and fastening device arranged on each riser in a position between the seabed and said length interval.
  • the device is characterized in that it further comprises: a chain arranged from each fastening device to the seabed, wherein the upper part of the chain is fastened to the fastening device, and a lower part of the chain is fastened to a fastening point provided at the seabed, the weight of the chain is adapted such that a number of chain links in normal operation will be lifted from the seabed and a number of chain links will rest at the seabed, where said number will vary according to varying load(s).
  • a chain means a chain.
  • a chain can also mean a wire with weight elements or a rope with weight elements, where the weight elements are equivalent to chain links which in a varying number can be lifted up from or laid down at the seabed.
  • fastening point is meant any fastening point, for instance an anchor, deadman or a pole.
  • the position at the sea surface is a point of introduction or a point of attachment/area just below on or above the sea surface, for instance a turret in a FPSO (Floating Production Storage and Offloading) or a connection area or connection point on a floating platform.
  • Each chain is preferably arranged so that it during normal operation will assume a chain line form from the fastening device to the seabed, wherein said chain line form is laying below, but mainly parallel to, the lower part of the riser.
  • it is preferably the resultant force from the chains which is parallel to the lower part of the riser.
  • the invention is illustrated by a figure, figure 1, illustrating a device according to the present invention of a flexible riser.
  • figure 1 illustrates an embodiment with flexible riser 1 provided from a seabed 2 to a position 3 on or near a sea surface, comprising at least one intermediate length interval 4 with buoyancy devices 5 provided on or to the riser, so that the riser achieves a positive buoyancy in said length interval and adapts a concave form above the seabed in said length interval.
  • Further fastening device 6 is illustrated provided on the riser in a position between the seabed and said length interval, a chain 7 provided from the fastening device to the seabed, where an upper part/end of sea chain is fastened to the fastening device, an anchor 8 is provided on the seabed and a lower part/end of the chain is fastened to the anchor, the weight of the chain is adapted so that varying number of chain links will be lifted from the seabed and a varying number of chain links will lay on the seabed in accordance with varying loads on the riser.
  • the lower part of the riser from a turning point between the seabed and the length interval with buoyancy devices, is adapting a chain line form which extends downward and further away from the position on or near the sea surface.
  • the upper part of the chain is adapting a chain line form which extends downwards and further away from the position on or near the sea surface.
  • the lower part of the riser and the chain are preferably arranged such that the angel between the riser and the chain always will be small, preferably in the area of 0 to 30°.
  • the fastening device is preferably clamp(s), alternatively other fastening devices can be utilized. Normally, the anchor does not absorb any load since the chain is functioning as an anchoring during normal operating conditions.
  • the size and the holding power for the anchor can thus be reduced compared with similar devices for risers. Further chock loads of the lower part of the risers is avoided since provision of a varying number of chain links at the seabed gives a varying weight of the chain and thus varying force from the chain upon the fastening device.
  • the weight of the chain is preferably adapted such that the entire chain is tensioned from the seabed only at extreme loads, while at maximum weight of the risers, one or more of the chain links are lifted from the seabed.
  • the extend of the buoyancy devices on the riser may be reduced compared with known devices with tension anchoring because the chain is not tensioned by the buoyancy from the intermediate part of the riser.
  • Important functions for the chain arrangement are also to limit or prevent movement of the riser from a vertical plane in the lengthwise direction of the riser, and limit so called “walking" out of the plane of the part of the riser situated at the seabed.
  • the arrangment of the lower part of the riser and the chain are favourably such that the resultant force from the chain effecting the riser and the tension of the riser downwards toward the seabed, by positioning of the fastening device, meet or principally meet the length interval where the buoyancy devices are arranged on or fastened to the riser.
  • the inclination of the riser at the fastening device is thus favourably such that a tangent of the inclination of the riser at the fastening device, in an extension in an upward direction, meets the length interval with buoyancy devices or below said length interval, while an extension of the direction of the chain in the upper part of the chain meets said length interval or above said length interval.
  • the part of the riser which always will remain at the seabed that is, the part that lies on the seabed even if all of the anchor chain links are lifted from the seabed and the chain is kept tensioned, may optionally be fastened to the seabed.
  • Different embodiments of the invention are possible when several risers are to be provided.
  • Preferably several risers are provided parallel or mainly parallel having one anchor provided between each riser, so that each anchor between two risers has fastened two chains to itself, one to each neighbouring riser.
  • N risers are provided parallel
  • N+l anchors are provided, wherein one anchor is provided between each riser and one anchor is provided outermost at each outside of the mainly parallel risers
  • 2N chains are provided, wherein each anchor between two risers is having two chains fastened to itself, one for each neighbouring riser, and each of the outermost risers has fastened to itself a chain to the respective anchor at the outside of the mainly parallel risers.
  • the risers are preferably arranged close to each other at the upper end at the sea surface, which is meant to be covered by the term mainly parallel.
  • each chain can be connected in the lower end to a separate anchor. It is considered more advantageous to have two chains provided to each anchor located between risers since this will limit the number of anchors.
  • inventions are for instance to provide several risers in the form of fan from for instance a floating production vessel, or variants with both risers arranged in the form of a fan and mainly parallel arranged risers.
  • risers but also hoses, umbilicals and cables can be provided according to the invention.
  • one or more flexible riser, umbilicals, hoses and cables can be bundled and provided according to the invention.
  • assembling of flexible risers according to the invention is also meant bundles of risers or other cable or hose formed bodies, individually or bundled with assembly according to the attached patent claims.

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  • Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Mining & Mineral Resources (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Environmental & Geological Engineering (AREA)
  • Fluid Mechanics (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geochemistry & Mineralogy (AREA)
  • Earth Drilling (AREA)
  • Supports For Pipes And Cables (AREA)

Abstract

Assembly of flexible risers, wherein each riser comprises an upper part extending as a chain line downward and away from position at a sea surface, an intermediate part with a length interval having buoyancy devices provided on or to the riser such that the riser within said length interval obtains positive buoyancy and the intermediate part assume a concave form directed towards the seabed, and the lower part extending as a chain line further downwards and away from the position at the sea surface to a seabed and fastening device provided on each riser in a position between the seabed and said length interval, characterized in that the assembly further comprises: a chain provided from each of the fastening devices to the seabed, wherein the upper end of the chain is fastened to the fastening device and a lower end of the chain is fastened to a fastening point provided at the seabed, wherein the weight of the chain adapted such that a number of chain links will be lifted from the seabed and a number of chain links will lay on the seabed at normal operation, said number varies according to varying loads.

Description

Title:
Assembly of flexible riser systems
Field of the invention
The present invention relates to flexible risers, cables and the like, and in particular to assembly of flexible riser, cables and the like from a sub-sea position to a position at the surface of the sea.
Background of the invention and prior art
For transfer of fluids, such as oil and gas from a seabed level to a level at or near the sea surface, risers are used. If fluids are to be transferred between a level at sea bottom and a floating installation or another installation having a variable position, risers are used in the form of flexible pipes. There are many solutions available how one or more flexible pipes can be arranged from a sea bottom to position at the surface so that the installation can be made conveniently, the length of the flexible risers not being of an excessive length and the load on the risers is limited and the operating lifetime for the risers are as long as possible. The American Petroleum Institute has published a recommended practice for assembling risers, API RP 17B, where the most common forms of assembling, such as lazy wave and steep wave, are described.
In the patent application US 2007/0081862 Al is described assembly of a riser wherein a connecting device is firmly attached from a connecting point on the riser to an anchor device, the connecting device being arranged mainly to limit an upward movement of the connection point. Thus movement of the riser is limited or eliminated where the riser reaches the seabed. In addition, fatigue of the riser, particularly where the riser reaches the seabed, is considerably limited.
In the patent application NO 306826 is described an assembly of a riser, wherein one or more weight elements are introduced to enclose the riser at the lower part of the riser. In one embodiment there is disclosed that at least one of the weight elements is attached to a chain at the convex side of the lower part of the riser and with buoyancy device connected to the chain in order to provide the lower part of the riser with an essential horizontal force. In the patent publication NO 300233, is disclosed an assembly of a riser, where said riser is known under the name "pliant wave". For the assembly pliant wave it is necessary to utilize a tight anchoring, that is a tension/tensile anchoring of the lower part of the riser to a stationary point at the seabed. In order to maintain the tension/tensile strength of the anchoring, is necessary to use an extensive arrangement of buoyancy devices in the upper part of the riser, as well as utilization of a large anchor.
The tension/tensile anchoring ensures that the flexible pipe is not bended more than what minimum bending radius allows. There is need in the art for means of flexible risers, with advantageous properties compared with said prior art.
Summary of the invention
The above mentioned need is met by the present invention providing means of flexible risers, wherein each riser comprises an upper part extending as a chain line downward and away from a position at the sea surface, an intermediate part with a length interval with buoyancy devices arranged on or attached to the riser, in order to provide a positive buoyancy in said length interval, and the intermediate part assuming a concave form directed towards the seabed, and a lower part extending as a chain line further down and away from the position at the sea surface to a seabed and fastening device arranged on each riser in a position between the seabed and said length interval.
The device is characterized in that it further comprises: a chain arranged from each fastening device to the seabed, wherein the upper part of the chain is fastened to the fastening device, and a lower part of the chain is fastened to a fastening point provided at the seabed, the weight of the chain is adapted such that a number of chain links in normal operation will be lifted from the seabed and a number of chain links will rest at the seabed, where said number will vary according to varying load(s).
Preferably the term a chain means a chain. However, a chain can also mean a wire with weight elements or a rope with weight elements, where the weight elements are equivalent to chain links which in a varying number can be lifted up from or laid down at the seabed. With the term fastening point is meant any fastening point, for instance an anchor, deadman or a pole.
The position at the sea surface is a point of introduction or a point of attachment/area just below on or above the sea surface, for instance a turret in a FPSO (Floating Production Storage and Offloading) or a connection area or connection point on a floating platform. Each chain is preferably arranged so that it during normal operation will assume a chain line form from the fastening device to the seabed, wherein said chain line form is laying below, but mainly parallel to, the lower part of the riser. However, by arranging more than one chain from a fastening device, it is preferably the resultant force from the chains which is parallel to the lower part of the riser. Thus both the lower part of the risers, laying below a turning point below the length interval with buoyancy devices, and the chains assume a chain line form, where the lower part thereof extends further away from the position at the sea surface.
Figures
The invention is illustrated by a figure, figure 1, illustrating a device according to the present invention of a flexible riser.
Detailed description Reference is made to figure 1 which illustrates an embodiment with flexible riser 1 provided from a seabed 2 to a position 3 on or near a sea surface, comprising at least one intermediate length interval 4 with buoyancy devices 5 provided on or to the riser, so that the riser achieves a positive buoyancy in said length interval and adapts a concave form above the seabed in said length interval. Further fastening device 6 is illustrated provided on the riser in a position between the seabed and said length interval, a chain 7 provided from the fastening device to the seabed, where an upper part/end of sea chain is fastened to the fastening device, an anchor 8 is provided on the seabed and a lower part/end of the chain is fastened to the anchor, the weight of the chain is adapted so that varying number of chain links will be lifted from the seabed and a varying number of chain links will lay on the seabed in accordance with varying loads on the riser. As shown in figure 1, the lower part of the riser, from a turning point between the seabed and the length interval with buoyancy devices, is adapting a chain line form which extends downward and further away from the position on or near the sea surface. Similarly, the upper part of the chain is adapting a chain line form which extends downwards and further away from the position on or near the sea surface. The lower part of the riser and the chain are preferably arranged such that the angel between the riser and the chain always will be small, preferably in the area of 0 to 30°. The fastening device is preferably clamp(s), alternatively other fastening devices can be utilized. Normally, the anchor does not absorb any load since the chain is functioning as an anchoring during normal operating conditions. The size and the holding power for the anchor can thus be reduced compared with similar devices for risers. Further chock loads of the lower part of the risers is avoided since provision of a varying number of chain links at the seabed gives a varying weight of the chain and thus varying force from the chain upon the fastening device. The weight of the chain is preferably adapted such that the entire chain is tensioned from the seabed only at extreme loads, while at maximum weight of the risers, one or more of the chain links are lifted from the seabed. Furthermore, the extend of the buoyancy devices on the riser may be reduced compared with known devices with tension anchoring because the chain is not tensioned by the buoyancy from the intermediate part of the riser.
Important functions for the chain arrangement are also to limit or prevent movement of the riser from a vertical plane in the lengthwise direction of the riser, and limit so called "walking" out of the plane of the part of the riser situated at the seabed.
The arrangment of the lower part of the riser and the chain are favourably such that the resultant force from the chain effecting the riser and the tension of the riser downwards toward the seabed, by positioning of the fastening device, meet or principally meet the length interval where the buoyancy devices are arranged on or fastened to the riser. The inclination of the riser at the fastening device is thus favourably such that a tangent of the inclination of the riser at the fastening device, in an extension in an upward direction, meets the length interval with buoyancy devices or below said length interval, while an extension of the direction of the chain in the upper part of the chain meets said length interval or above said length interval. Such arrangement is preferred due to prevailing forces, and results in that the extent of buoyancy devices and the weight of the chain and the size of the anchor all can be limited. The part of the riser which always will remain at the seabed, that is, the part that lies on the seabed even if all of the anchor chain links are lifted from the seabed and the chain is kept tensioned, may optionally be fastened to the seabed. Different embodiments of the invention are possible when several risers are to be provided. Preferably several risers are provided parallel or mainly parallel having one anchor provided between each riser, so that each anchor between two risers has fastened two chains to itself, one to each neighbouring riser. In a preferred embodiment N risers are provided parallel, N+l anchors are provided, wherein one anchor is provided between each riser and one anchor is provided outermost at each outside of the mainly parallel risers, and 2N chains are provided, wherein each anchor between two risers is having two chains fastened to itself, one for each neighbouring riser, and each of the outermost risers has fastened to itself a chain to the respective anchor at the outside of the mainly parallel risers. The risers are preferably arranged close to each other at the upper end at the sea surface, which is meant to be covered by the term mainly parallel. Alternatively each chain can be connected in the lower end to a separate anchor. It is considered more advantageous to have two chains provided to each anchor located between risers since this will limit the number of anchors.
Other embodiments of the invention are for instance to provide several risers in the form of fan from for instance a floating production vessel, or variants with both risers arranged in the form of a fan and mainly parallel arranged risers.
Not only risers but also hoses, umbilicals and cables can be provided according to the invention. Furthermore, one or more flexible riser, umbilicals, hoses and cables can be bundled and provided according to the invention. With assembling of flexible risers according to the invention is also meant bundles of risers or other cable or hose formed bodies, individually or bundled with assembly according to the attached patent claims.

Claims

C l a i m s
1. Assembly of flexible risers, cables and/or the like (hereinafter called risers), wherein each riser comprises an upper part extending as a chain line downward and away from a position at the sea surface, an intermediate part with a length interval with buoyancy devices provided on or attached to the riser, so that the riser in said length interval obtains a positive buoyancy and the intermediate part assume a concave form directed towards the seabed, and lower part extending as a chain line further downwards and away from the position at the sea surface to the seabed and a fastening device provided on each riser in a position between the seabed and said length interval, characterized in that the assembly further comprises: a chain provided from each fastening device to the seabed, the upper end of the chain is fastened to the fastening device and a lower end of the chain is fastened to a fastening point arranged at the seabed, wherein the weight of the chain is adapted such that, at normal operation, a number of chain links will be lifted from the seabed and a number of chain links will lay at the seabed, said number varies according to varying loads.
2. Assembly according to claim 1, characterized in that each chain is arranged such that it assumes a chain line form from the fastening device to the seabed at normal operation, said chain line form is provided below, but mainly parallel to, the lower part of the riser.
3. Assembly according to claim 1, characterized in that the fastening device is a clamp.
4. Assembly according to claim 1, characterized in that the fastening point is an anchor which normally does not absorb any load since a number of chain links always will rest on the seabed during normal operation.
5. Assembly according to claim 1, characterized in that an extension of the direction of the upper part of the chain and an extension of the direction of the riser in the position at the fastening device mainly meet the length interval having buoyancy devices so that the resultant force from tension in the riser at the fastening device and tension from the chain mainly meet said length interval.
6. Assembly according to claim 1, characterized in that several risers are arranged parallel or mainly parallel, with an anchor provided between each riser, so that each anchor situated between two risers has two chains fastened, one to each neighbouring riser.
7. Assembly according to claim 1, characterized in that N riser are provided mainly parallel, N+ 1 anchors are provided, each anchor is provided between each riser and one anchor is provided outermost on each outside of the mainly parallel risers, and
2N chains are provided, each anchor between two risers has two chains fastened, one to each neighbouring riser, and each of the outermost risers has fastened a chain to the respective anchor at the outside of the mainly parallel risers
PCT/NO2009/000155 2008-04-29 2009-04-24 Assembly of flexible riser systems WO2009139636A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
DKPA201070078A DK201070078A (en) 2008-04-29 2010-03-01 Installation of flexible riser systems

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NO20082053A NO20082053L (en) 2008-04-29 2008-04-29 Arrangement of flexible risers
NO20082053 2008-04-29

Publications (1)

Publication Number Publication Date
WO2009139636A1 true WO2009139636A1 (en) 2009-11-19

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DK (1) DK201070078A (en)
NO (1) NO20082053L (en)
WO (1) WO2009139636A1 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2011150363A1 (en) * 2010-05-28 2011-12-01 Weatherford/Lamb, Inc. Deepwater completion installation and intervention system
WO2012143671A2 (en) 2011-04-18 2012-10-26 Magma Global Limited Subsea conduit system
CN107109907A (en) * 2014-12-22 2017-08-29 通用电气石油和天然气英国有限公司 Lift device assembly and the method for forming lifting device assembly

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4906137A (en) * 1988-02-24 1990-03-06 Coflexip Apparatus for transferring fluid between subsea floor and the surface
US5098323A (en) * 1989-07-14 1992-03-24 Single Buoy Moorings, Inc. Device for positioning of a buoy body
GB2311503A (en) * 1996-03-28 1997-10-01 Alcatel Kabel Norge As Anchoring a cable or riser pipe
WO1999066169A2 (en) * 1998-06-12 1999-12-23 Den Norske Stats Oljeselskap A.S Device related to risers
US6146052A (en) * 1997-04-29 2000-11-14 Kvaerner Oilfield Products A.S Dynamic control cable for use between a floating structure and a connection point on the seabed
US20020023580A1 (en) * 2000-02-08 2002-02-28 Brovig Rds Limited Mooring and flowline system
US20070081862A1 (en) * 2005-10-07 2007-04-12 Heerema Marine Contractors Nederland B.V. Pipeline assembly comprising an anchoring device and method for installing a pipeline assembly comprising an anchoring device

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4906137A (en) * 1988-02-24 1990-03-06 Coflexip Apparatus for transferring fluid between subsea floor and the surface
US5098323A (en) * 1989-07-14 1992-03-24 Single Buoy Moorings, Inc. Device for positioning of a buoy body
GB2311503A (en) * 1996-03-28 1997-10-01 Alcatel Kabel Norge As Anchoring a cable or riser pipe
US6146052A (en) * 1997-04-29 2000-11-14 Kvaerner Oilfield Products A.S Dynamic control cable for use between a floating structure and a connection point on the seabed
WO1999066169A2 (en) * 1998-06-12 1999-12-23 Den Norske Stats Oljeselskap A.S Device related to risers
US20020023580A1 (en) * 2000-02-08 2002-02-28 Brovig Rds Limited Mooring and flowline system
US20070081862A1 (en) * 2005-10-07 2007-04-12 Heerema Marine Contractors Nederland B.V. Pipeline assembly comprising an anchoring device and method for installing a pipeline assembly comprising an anchoring device

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2011150363A1 (en) * 2010-05-28 2011-12-01 Weatherford/Lamb, Inc. Deepwater completion installation and intervention system
US9068398B2 (en) 2010-05-28 2015-06-30 Weatherford/Lamb, Inc. Deepwater completion installation and intervention system
WO2012143671A2 (en) 2011-04-18 2012-10-26 Magma Global Limited Subsea conduit system
US9534452B2 (en) 2011-04-18 2017-01-03 Magma Global Limited Subsea conduit system
CN107109907A (en) * 2014-12-22 2017-08-29 通用电气石油和天然气英国有限公司 Lift device assembly and the method for forming lifting device assembly
CN107109907B (en) * 2014-12-22 2020-02-04 通用电气石油和天然气英国有限公司 Riser assembly and method of forming a riser assembly

Also Published As

Publication number Publication date
DK201070078A (en) 2010-03-01
NO20082053L (en) 2009-10-30

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