WO2024115397A1 - Process of anchoring a floating platform on a rocky seabed - Google Patents

Process of anchoring a floating platform on a rocky seabed Download PDF

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Publication number
WO2024115397A1
WO2024115397A1 PCT/EP2023/083187 EP2023083187W WO2024115397A1 WO 2024115397 A1 WO2024115397 A1 WO 2024115397A1 EP 2023083187 W EP2023083187 W EP 2023083187W WO 2024115397 A1 WO2024115397 A1 WO 2024115397A1
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WO
WIPO (PCT)
Prior art keywords
trench portion
line
anchor structure
median part
wall
Prior art date
Application number
PCT/EP2023/083187
Other languages
French (fr)
Inventor
Benoit CAILLET
Original Assignee
Totalenergies Onetech
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 Totalenergies Onetech filed Critical Totalenergies Onetech
Publication of WO2024115397A1 publication Critical patent/WO2024115397A1/en

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Classifications

    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D27/00—Foundations as substructures
    • E02D27/32—Foundations for special purposes
    • E02D27/52—Submerged foundations, i.e. submerged in open water
    • E02D27/525—Submerged foundations, i.e. submerged in open water using elements penetrating the underwater ground
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B21/00—Tying-up; Shifting, towing, or pushing equipment; Anchoring
    • B63B21/24—Anchors
    • B63B21/26—Anchors securing to bed
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B21/00—Tying-up; Shifting, towing, or pushing equipment; Anchoring
    • B63B21/24—Anchors
    • B63B21/30—Anchors rigid when in use
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D27/00—Foundations as substructures
    • E02D27/32—Foundations for special purposes
    • E02D27/52—Submerged foundations, i.e. submerged in open water
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B21/00—Tying-up; Shifting, towing, or pushing equipment; Anchoring
    • B63B21/24—Anchors
    • B63B21/26—Anchors securing to bed
    • B63B2021/267—Anchors securing to bed by penetration of anchor into the sea bed using water jets, e.g. by ground or sand fluidisation

Definitions

  • the present invention deals with a process of anchoring a floating platform on a rocky seabed, comprising connecting a mooring steel chain to an anchor structure and to the floating platform.
  • Drilled and grouted piles usually have a 3m diameter. Installing them requires digging a 20m deep hole, and filling the annulus between the pile and the rock with grout. They require investigating the seabed over a depth of more than 20m.
  • the solution of drilled and grouted piles is in fact very challenging for water depths where jack-ups cannot be jacked, e.g. for water depths over 60m.
  • drilling is subject to risks, such as weather and ocean conditions, and technical problems such as hole collapse, very hard rock, management of cuttings...
  • the number of drilling contractors is quite limited in the world.
  • Gravity based structures filled with sand and gravel represent an alternative. However, they lead to large structures occupying a surface of about 20m x 20m. They require thousands of tons of sand or gravel for ballasting. In the end, they are also quite expensive, and have a non-negligible environmental footprint because of their footprint and influence over the water column.
  • An aim of the invention is to provide an anchoring process adapted to a rocky seabed allowing reducing costs and environmental footprint.
  • the invention proposes a process of anchoring a floating platform on a rocky seabed, comprising the following steps:
  • the anchor structure comprising a median part located at a junction of the first trench portion and the second trench portion, and two lateral parts extending from the median part along the line respectively on either sides of the median part, the median part comprising more steel than the lateral parts per unit of length along the line,
  • the process comprises one or several of the following features, taken in isolation or any technically feasible combination:
  • the process comprises providing the first trench portion and the second trench portion includes digging the seabed along the line and along the transverse direction using a subsea trencher;
  • the process comprises injecting the grout includes using at least one grout line of the anchor structure, said grout line extending along the line, and/or using at least one stinger in order to inject at least part of the grout;
  • the median part comprises several steel plates approximately parallel to the transverse direction;
  • the median part comprises a first plurality of at least three plates parallel to each other, and a second plurality of at least three plates parallel to each, perpendicular to the plates of the first plurality, and connecting the plates of the of the first plurality one with the other;
  • the median part comprises a plate protruding transversely on which the mooring chain is attached;
  • each of the two lateral parts comprises a reinforcement cage fixed to the median part, the injected grout at least partly filling the reinforcement cage of the two lateral parts;
  • the anchor structure comprises a first wall extending along the line and approximately perpendicular to the transverse direction, the first wall forming part of the median part, and of the two lateral parts; and the two lateral parts respectively comprise a first sheet and a second sheet extending along the line and approximately perpendicular to the first wall, the first sheet and the third wall protruding transversely from the first wall opposite said transverse wall; - the first wall and the first sheet, and the first wall and the second sheet form “T” profiles;
  • the anchor structure comprises a second wall extending along the line and approximately perpendicular to the transverse direction, the second wall forming part of the median part and of the two lateral parts, the first sheet and the second sheet being fixed to the second wall;
  • the grout is also injected between the second wall and another transverse wall of the first trench portion opposite said transverse wall in the transverse direction;
  • the process comprises: connecting a second mooring steel chain to the median part; and, after curing of the injected grout, connecting the second mooring chain to a second floating platform, the second mooring chain having a portion in the second trench portion, on the other side of the portion of the mooring chain with respect to the anchor structure, the second floating platform being intended to apply a second traction force on the anchor structure transversely.
  • the invention also deals with an anchoring system adapted for anchoring a floating platform on a rocky seabed, the anchoring system comprising:
  • the anchor structure at least partly located in the first trench portion, the anchor structure comprising a median part located at a junction of the first trench portion and the second trench portion, and two lateral parts extending from the median part along the line respectively on either sides of the median part, the median part comprising more steel than the two lateral parts per unit of length along the line,
  • a mooring steel chain attached on the median part, on a side facing the second trench portion long the transverse direction, the mooring chain having a portion in the second trench portion and being intended to be connected to the floating platform, the floating platform being intended to apply a traction force on the anchor structure transversely from the first trench portion toward the second trench portion.
  • FIG. 1 is a schematic upper view of an anchoring system according to the invention
  • FIG. 2 is a schematic perspective view of the anchoring system shown in Figure 1 , a second mooring chain being not shown again,
  • FIG. 3 is a schematic perspective view of the anchor structure of the anchoring system shown in Figures 1 and 2,
  • FIG. 4 is a schematic perspective view of the median part of the anchor structure shown in Figure 3.
  • FIGS 5 and 6 are schematic side views showing successive phases of the construction of the anchoring system shown in Figures 1 and 2, in order to illustrate a process according to the invention.
  • the anchoring system 10 is adapted for anchoring a floating platform 12 (symbolized by a square in Figure 1 ) to a rocky seabed 14.
  • the anchoring system 10 is also adapted for anchoring a second floating platform 13 (symbolized by a square in Figure 1).
  • the anchoring system 10 is a mutual one, which allows using a seabed location for anchoring several floating platforms.
  • rocky seabed it is meant here that the seabed 14 comprises rocks 16, to which the anchoring system is fixed.
  • the strength of the anchoring system 10 depends on the strength of rock (from very weak to very strong) and the level of fracturation, from highly weathered/fractured (Rock Quality Designation: worse) to no weathered/fractured (Rock Quality Designation: excellent).
  • the platform 12 for example hosts a wind turbine (not shown).
  • the platform 12 and the second platform 13 float on or in a body of water 18 (see, ocean or lake) extending over the seabed 14.
  • the floating platforms 12, 13 may float at the surface of the body of water 18, or below the surface.
  • the anchoring system 10 comprises a first trench portion 20 located in the seabed 14 and extending along a line L, and a second trench portion 21 extending from the line L along a transverse direction T.
  • the anchoring system 10 comprises an anchor structure 22 located in the first trench portion, and grout 24 located at least between the anchor structure 22 and transverse wall 25 of the first trench portion 20.
  • the anchoring system 10 comprises a mooring steel chain 26 connected to the floating platform 12 and to the anchor structure 22.
  • the anchoring system 10 comprises a second mooring steel chain 28 connected to the second platform 13 and to the anchor structure 22.
  • the anchoring system 10 is advantageously designed to resist traction forces F, F2 applied by the mooring chain 26 and the second mooring chain 28 on the anchor structure 22, for example up to 10000kN each.
  • the anchoring system 10 is advantageously designed to have a lifespan of at least 25 years.
  • the line L is for example straight and horizontal.
  • the line L may be inclined in order to follow a seabed 14 with a gentle slope.
  • the traction forces F, F2 are for example parallel to the seabed 14 (case of a catenary mooring system). As a variant (not shown), the traction forces F, F2 may have a component perpendicular to the seabed 14.
  • the first trench portion 20 and the second trench portion 21 may be natural, from previous digging, or preferably from dedicated digging.
  • the first trench portion 20 for example has a U-shaped section perpendicularly to the line L.
  • the first trench portion 20 for example has a length L1 along the line L comprised between 5.0m and 40m, advantageously between 10m and 30m.
  • the first trench portion 20 for example has an average horizontal width L2 perpendicularly to the line L, said width being comprised between 0.3m and 2.5m, advantageously between 0.5m and 2.0m.
  • the first trench portion 20 for example has an average depth L3 comprised between 1 ,0m and 5.0m, advantageously between 1 ,0m and 2.5m.
  • the second trench portion 21 and the first trench portion 20 define an angle comprised between 75° and 105°.
  • the second trench portion 21 is perpendicular to the line L.
  • the second trench portion 21 has a U-shaped or V-shaped section perpendicularly to the transverse direction T.
  • the second trench portion 21 has a same average width L4 along the line L, and a same average depth L3 as the first trench portion 20.
  • the second trench portion 21 has a first part 30 located on one side along the transverse direction T with respect to the first trench portion 20, and a second part 32 located on the other side along the transverse direction T with respect to the first trench portion.
  • the first part 30 receives the mooring chain 26, and has a length L5 along the transverse direction T, for example comprised between 5.0m and 40m, advantageously between 10m and 30m.
  • the second part 32 receives the second mooring chain 28 and has a length L6.
  • the length L6 is shorter than the length L5.
  • the second part 32 may be just a consequence of the digging process and is then much shorter than the first part 30.
  • the length L6 is similar to the length L5.
  • the anchor structure 22 is entirely located in the first trench portion 20. In other words, the anchor structure 22 is below the seabed level.
  • the anchor structure 22 advantageously extends over more than 90% of the first trench portion 20 along the line L.
  • the anchor structure 22 is advantageously fully surrounded by the grout 24 around the line L.
  • the anchor structure 22 comprises a median part 34 located at a junction 36 of the first trench portion 20 and the second trench portion 21 , and two lateral parts 38, 40 extending from the median part along the line L respectively on either sides of the median part.
  • the anchor structure 22 comprises at least one grout line 42 ( Figure 1 ) extending along the line L.
  • the anchor structure 22 comprises a first wall 44 extending along the line L and approximately perpendicular to the transverse direction T, the first wall forming part of the median part 34, and of the lateral parts 38, 40.
  • the anchor structure 22 is symmetric with respect to a median plan P perpendicular to the line L.
  • the anchor structure 22 is for example made of steel.
  • the median part 34 comprises more steel than the lateral parts 38, 40 per unit of length along the line L.
  • the median part 34 advantageously comprises several steel plates 46 approximately parallel to the transverse direction T.
  • the median part 34 comprises a first plurality 46A of at least three plates parallel to each other, and a second plurality 46B of at least three plates parallel to each other, perpendicular to the plates of the first plurality 46A, and connecting the plates of the of the first plurality one with the other.
  • the median part 34 advantageously comprises a plate 48 (figures 2 and 3) protruding transversely on which the mooring chain 26 is attached.
  • the median part 34 forms a boxed area 50.
  • the lateral parts 38, 40 respectively comprise a first sheet 52 and a second sheet 54 extending along the line L and approximately perpendicular to the first wall 44, the first sheet and the second sheet protruding transversely from the first wall opposite the transverse wall 25 of the first trench portion 20.
  • first wall 44 and the first sheet 52, and the first wall 44 and the second sheet 54 form “T” profiles.
  • a second wall 56 of the anchor structure 22 extends along the line L and is approximately perpendicular to the transverse direction T, the second wall 56 forming part of the median part 34 and of the lateral parts 38, 40, the first sheet 52 and the second sheet 54 being fixed to the second wall 56.
  • each of the two lateral parts 38, 40 does not comprise walls or sheets, but is formed by a reinforcement cage fixed to the median part 34, the injected grout 24 at least partly filling the reinforcement cage.
  • the median part 34 and the two lateral parts 38, 40 do not comprise walls or sheets, but are formed by a reinforcement cage, the injected grout 24 at least partly filling said reinforcement cage.
  • the mooring chain 26 has a portion 58 in the second trench portion 21 , the floating platform 12 applying a traction force F on the anchor structure 22 transversely from the first trench portion 20 toward the second trench portion 21.
  • the mooring chain 26 is connected to the median part 34, advantageously at a certain depth L7 with respect to an upper part 60 of the anchor structure, for example to the plate 48.
  • the depth L7 is advantageously comprised between 40% and 75% of the depth L3, and is for example approximately half of the depth L3.
  • the second mooring chain 28 has a portion 62 in the second trench portion 21 , on the other side of the portion 58 of the mooring chain 26 with respect to the anchor structure 22, the second platform 13 applying a second traction force F2 on the anchor structure transversely.
  • the grout 24 aims at ensuring a sealing of the anchor structure 22 with the surrounding seabed 14, at least with the transverse wall 25.
  • the grout 24 is located between the first wall 44 of the anchor structure 22 and the transverse wall 25, and advantageously between the second wall 56 of the anchor structure and a transverse wall 64 of the first trench portion 20 opposite the transverse wall 25.
  • the grout 24 fully surrounds the anchor structure 22.
  • the grout 24 is for example a Portland grout and is adapted for curing underwater.
  • the grout 24 advantageously fills the first trench portion 20 up to seabed level over at least 90% of the anchor structure 22 along the line L.
  • the grout 24 is adapted to develop a shear friction against the first trench portion 20 rocky walls of as a minimum 100 kPa.
  • the seabed 14 is first surveyed for example by a remotely operated vehicle 66. Goal is to detect possible obstacles which could cause issues with the installation. One may also rely on previous knowledge of the seabed 14 such as bathymetry and seabed imagery.
  • first trench portion 20 and the second trench portion 21 are provided in the seabed 14.
  • first trench portion 20 and the second trench portion 21 are dug using a subsea trencher 68 commonly used for pipeline or cables burial.
  • the remotely operated vehicle 66 and the subsea trencher 68 are equipment known in themselves and available from the market.
  • the first trench portion 20 and/or the second trench portion 21 are existing one(s), and do not have to be dug.
  • the first trench portion 20 and is cleaned, advantageously using water jets (not shown) directed at the walls 25, 64 of the first trench portion 20.
  • the jets are for example produced by the remotely operated vehicle 66.
  • the anchor structure 22 is installed, for example pre-assembled and lowered, in the first trench portion 20.
  • the mooring chain 26, and in the example the second mooring chain 28, are attached to the median part 31 of the anchor structure 22.
  • grout is injected in the first trench portion 20 at least between the anchor structure 22 and the transverse wall 25, in the example via the grout line 42 from a source (not shown), in order to obtain the grout 24.
  • grout is injected using a stinger (not shown).
  • grouting is stopped when the first trench portion 20 is full of grout, or at least when the anchor structure 22 is surrounded by grout.
  • the mooring chain 26 After curing, the mooring chain 26 is connected to the floating platform 12, and is tensioned. In the example, the same is performed with the second mooring chain 28 and the second floating platform 13.
  • the floating platforms 12, 13 may exert the traction forces F, F2 on the anchor structure 22 within a reasonable angle with respect to the transverse direction T. Thanks to the above features, the anchoring process is adapted to the rocky seabed 14 and preferably catenary mooring solutions, and allows reducing costs and the environmental footprint.
  • the anchoring process advantageously allows anchoring several floating platforms.

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  • General Engineering & Computer Science (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Mining & Mineral Resources (AREA)
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  • Piles And Underground Anchors (AREA)

Abstract

Process of anchoring a floating platform on a rocky seabed (14), comprising: - providing a first trench portion (20) and a second trench portion (21) in the seabed, the first trench portion extending along a line (L), and the second trench portion extending in a transverse direction (T), - installing an anchor structure (22) in the first trench portion, the anchor structure comprising a median part (34), and two lateral parts (38, 40) on either sides of the median part, the median part comprising more steel than the lateral parts, - attaching a mooring steel chain (26) on the median part, - injecting grout (24) at least between the anchor structure and a transverse wall (25) of the first trench portion, - connecting the mooring chain to the floating platform, the mooring chain having a portion (58) in the second trench portion. Corresponding anchoring system.

Description

Process of anchoring a floating platform on a rocky seabed
The present invention deals with a process of anchoring a floating platform on a rocky seabed, comprising connecting a mooring steel chain to an anchor structure and to the floating platform.
It also deals with a corresponding anchoring system.
The growing industry of offshore wind and oil and gas projects pushes states or developers to consider more and more offshore areas. In some of them, soil conditions may represent a challenge to common industry practices for the installation of mooring points, such as drag anchors, driven piles or suction piles. Indeed, these technologies are not suited to a rocky seabed.
Drilled and grouted piles usually have a 3m diameter. Installing them requires digging a 20m deep hole, and filling the annulus between the pile and the rock with grout. They require investigating the seabed over a depth of more than 20m. The solution of drilled and grouted piles is in fact very challenging for water depths where jack-ups cannot be jacked, e.g. for water depths over 60m. There is also limited experience in drilling with a vessel using dynamic positioning and a heave compensated platform. Moreover, drilling is subject to risks, such as weather and ocean conditions, and technical problems such as hole collapse, very hard rock, management of cuttings... The number of drilling contractors is quite limited in the world.
This explains why using piles for anchoring purposes is expensive.
Gravity based structures filled with sand and gravel represent an alternative. However, they lead to large structures occupying a surface of about 20m x 20m. They require thousands of tons of sand or gravel for ballasting. In the end, they are also quite expensive, and have a non-negligible environmental footprint because of their footprint and influence over the water column.
An aim of the invention is to provide an anchoring process adapted to a rocky seabed allowing reducing costs and environmental footprint.
To this end, the invention proposes a process of anchoring a floating platform on a rocky seabed, comprising the following steps:
- providing a first trench portion and a second trench portion in the seabed, the first trench portion extending along a line, and the second trench portion extending from the line in a transverse direction,
- installing an anchor structure in the first trench portion, the anchor structure comprising a median part located at a junction of the first trench portion and the second trench portion, and two lateral parts extending from the median part along the line respectively on either sides of the median part, the median part comprising more steel than the lateral parts per unit of length along the line,
- attaching a mooring steel chain on the median part, on a side facing the second trench portion along the transverse direction,
- injecting grout in the first trench portion, at least between the anchor structure and a transverse wall of the first trench portion, and
- after curing of the injected grout, connecting the mooring chain to the floating platform, the mooring chain having a portion in the second trench portion, the floating platform being intended to apply a traction force on the anchor structure transversely from the first trench portion toward the second trench portion.
In other embodiments, the process comprises one or several of the following features, taken in isolation or any technically feasible combination:
- the process comprises providing the first trench portion and the second trench portion includes digging the seabed along the line and along the transverse direction using a subsea trencher;
- the line is straight;
- the process comprises injecting the grout includes using at least one grout line of the anchor structure, said grout line extending along the line, and/or using at least one stinger in order to inject at least part of the grout;
- the median part comprises several steel plates approximately parallel to the transverse direction;
- the median part comprises a first plurality of at least three plates parallel to each other, and a second plurality of at least three plates parallel to each, perpendicular to the plates of the first plurality, and connecting the plates of the of the first plurality one with the other;
- the median part forms a boxed area;
- the median part comprises a plate protruding transversely on which the mooring chain is attached;
- each of the two lateral parts comprises a reinforcement cage fixed to the median part, the injected grout at least partly filling the reinforcement cage of the two lateral parts;
- the anchor structure comprises a first wall extending along the line and approximately perpendicular to the transverse direction, the first wall forming part of the median part, and of the two lateral parts; and the two lateral parts respectively comprise a first sheet and a second sheet extending along the line and approximately perpendicular to the first wall, the first sheet and the third wall protruding transversely from the first wall opposite said transverse wall; - the first wall and the first sheet, and the first wall and the second sheet form “T” profiles;
- the anchor structure comprises a second wall extending along the line and approximately perpendicular to the transverse direction, the second wall forming part of the median part and of the two lateral parts, the first sheet and the second sheet being fixed to the second wall;
- the grout is also injected between the second wall and another transverse wall of the first trench portion opposite said transverse wall in the transverse direction; and
- the process comprises: connecting a second mooring steel chain to the median part; and, after curing of the injected grout, connecting the second mooring chain to a second floating platform, the second mooring chain having a portion in the second trench portion, on the other side of the portion of the mooring chain with respect to the anchor structure, the second floating platform being intended to apply a second traction force on the anchor structure transversely.
The invention also deals with an anchoring system adapted for anchoring a floating platform on a rocky seabed, the anchoring system comprising:
- at least a first trench portion and a second trench portion located in the seabed, the first trench portion extending along a line, and the second trench portion extending from the line in a transverse direction,
- an anchor structure at least partly located in the first trench portion, the anchor structure comprising a median part located at a junction of the first trench portion and the second trench portion, and two lateral parts extending from the median part along the line respectively on either sides of the median part, the median part comprising more steel than the two lateral parts per unit of length along the line,
- grout located in the first trench portion, at least between the anchor structure and a transverse wall of the first trench portion, and
- a mooring steel chain attached on the median part, on a side facing the second trench portion long the transverse direction, the mooring chain having a portion in the second trench portion and being intended to be connected to the floating platform, the floating platform being intended to apply a traction force on the anchor structure transversely from the first trench portion toward the second trench portion.
The invention and its advantages will be better understood upon reading the following description, given solely by way of example and with reference to the appended drawings, in which:
- Figure 1 is a schematic upper view of an anchoring system according to the invention, - Figure 2 is a schematic perspective view of the anchoring system shown in Figure 1 , a second mooring chain being not shown again,
- Figure 3 is a schematic perspective view of the anchor structure of the anchoring system shown in Figures 1 and 2,
- Figure 4 is a schematic perspective view of the median part of the anchor structure shown in Figure 3, and
- Figures 5 and 6 are schematic side views showing successive phases of the construction of the anchoring system shown in Figures 1 and 2, in order to illustrate a process according to the invention.
An anchoring system 10 according to the invention will now be described with reference to Figures 1 to 4.
The anchoring system 10 is adapted for anchoring a floating platform 12 (symbolized by a square in Figure 1 ) to a rocky seabed 14.
In the example, the anchoring system 10 is also adapted for anchoring a second floating platform 13 (symbolized by a square in Figure 1). In this case, the anchoring system 10 is a mutual one, which allows using a seabed location for anchoring several floating platforms.
By “rocky” seabed, it is meant here that the seabed 14 comprises rocks 16, to which the anchoring system is fixed. The strength of the anchoring system 10 depends on the strength of rock (from very weak to very strong) and the level of fracturation, from highly weathered/fractured (Rock Quality Designation: worse) to no weathered/fractured (Rock Quality Designation: excellent).
The platform 12 for example hosts a wind turbine (not shown). The platform 12 and the second platform 13 float on or in a body of water 18 (see, ocean or lake) extending over the seabed 14. The floating platforms 12, 13 may float at the surface of the body of water 18, or below the surface.
The anchoring system 10 comprises a first trench portion 20 located in the seabed 14 and extending along a line L, and a second trench portion 21 extending from the line L along a transverse direction T. The anchoring system 10 comprises an anchor structure 22 located in the first trench portion, and grout 24 located at least between the anchor structure 22 and transverse wall 25 of the first trench portion 20.
The anchoring system 10 comprises a mooring steel chain 26 connected to the floating platform 12 and to the anchor structure 22.
In the example, the anchoring system 10 comprises a second mooring steel chain 28 connected to the second platform 13 and to the anchor structure 22. The anchoring system 10 is advantageously designed to resist traction forces F, F2 applied by the mooring chain 26 and the second mooring chain 28 on the anchor structure 22, for example up to 10000kN each. The anchoring system 10 is advantageously designed to have a lifespan of at least 25 years.
The line L is for example straight and horizontal.
As a variant (not shown), the line L may be inclined in order to follow a seabed 14 with a gentle slope.
The traction forces F, F2 are for example parallel to the seabed 14 (case of a catenary mooring system). As a variant (not shown), the traction forces F, F2 may have a component perpendicular to the seabed 14.
The first trench portion 20 and the second trench portion 21 may be natural, from previous digging, or preferably from dedicated digging.
As symbolized in Figure 6, the first trench portion 20 for example has a U-shaped section perpendicularly to the line L.
The first trench portion 20 for example has a length L1 along the line L comprised between 5.0m and 40m, advantageously between 10m and 30m.
The first trench portion 20 for example has an average horizontal width L2 perpendicularly to the line L, said width being comprised between 0.3m and 2.5m, advantageously between 0.5m and 2.0m.
The first trench portion 20 for example has an average depth L3 comprised between 1 ,0m and 5.0m, advantageously between 1 ,0m and 2.5m.
For example, the second trench portion 21 and the first trench portion 20 define an angle comprised between 75° and 105°. In the example, the second trench portion 21 is perpendicular to the line L.
Advantageously, the second trench portion 21 has a U-shaped or V-shaped section perpendicularly to the transverse direction T.
For example, the second trench portion 21 has a same average width L4 along the line L, and a same average depth L3 as the first trench portion 20.
In the example, the second trench portion 21 has a first part 30 located on one side along the transverse direction T with respect to the first trench portion 20, and a second part 32 located on the other side along the transverse direction T with respect to the first trench portion.
For example, the first part 30 receives the mooring chain 26, and has a length L5 along the transverse direction T, for example comprised between 5.0m and 40m, advantageously between 10m and 30m. In the example, the second part 32 receives the second mooring chain 28 and has a length L6.
In Figure 1 , the length L6 is shorter than the length L5.
As a variant, if there is no second mooring chain, the second part 32 may be just a consequence of the digging process and is then much shorter than the first part 30.
As a preferred variant (not shown), the length L6 is similar to the length L5.
In the example, the anchor structure 22 is entirely located in the first trench portion 20. In other words, the anchor structure 22 is below the seabed level. The anchor structure 22 advantageously extends over more than 90% of the first trench portion 20 along the line L.
The anchor structure 22 is advantageously fully surrounded by the grout 24 around the line L.
As shown in Figures 1 to 3, the anchor structure 22 comprises a median part 34 located at a junction 36 of the first trench portion 20 and the second trench portion 21 , and two lateral parts 38, 40 extending from the median part along the line L respectively on either sides of the median part.
According to a particular embodiment, the anchor structure 22 comprises at least one grout line 42 (Figure 1 ) extending along the line L.
For example, the anchor structure 22 comprises a first wall 44 extending along the line L and approximately perpendicular to the transverse direction T, the first wall forming part of the median part 34, and of the lateral parts 38, 40.
For example, the anchor structure 22 is symmetric with respect to a median plan P perpendicular to the line L.
The anchor structure 22 is for example made of steel.
The median part 34 comprises more steel than the lateral parts 38, 40 per unit of length along the line L.
The median part 34 advantageously comprises several steel plates 46 approximately parallel to the transverse direction T.
For example, as shown in Figure 4, the median part 34 comprises a first plurality 46A of at least three plates parallel to each other, and a second plurality 46B of at least three plates parallel to each other, perpendicular to the plates of the first plurality 46A, and connecting the plates of the of the first plurality one with the other.
The median part 34 advantageously comprises a plate 48 (figures 2 and 3) protruding transversely on which the mooring chain 26 is attached.
For example, the median part 34 forms a boxed area 50. Advantageously, the lateral parts 38, 40 respectively comprise a first sheet 52 and a second sheet 54 extending along the line L and approximately perpendicular to the first wall 44, the first sheet and the second sheet protruding transversely from the first wall opposite the transverse wall 25 of the first trench portion 20.
For example, the first wall 44 and the first sheet 52, and the first wall 44 and the second sheet 54 form “T” profiles.
In a particular embodiment, a second wall 56 of the anchor structure 22 extends along the line L and is approximately perpendicular to the transverse direction T, the second wall 56 forming part of the median part 34 and of the lateral parts 38, 40, the first sheet 52 and the second sheet 54 being fixed to the second wall 56.
As a variant (not shown), each of the two lateral parts 38, 40 does not comprise walls or sheets, but is formed by a reinforcement cage fixed to the median part 34, the injected grout 24 at least partly filling the reinforcement cage.
As another variant (not shown), the median part 34 and the two lateral parts 38, 40 do not comprise walls or sheets, but are formed by a reinforcement cage, the injected grout 24 at least partly filling said reinforcement cage.
The mooring chain 26 has a portion 58 in the second trench portion 21 , the floating platform 12 applying a traction force F on the anchor structure 22 transversely from the first trench portion 20 toward the second trench portion 21. The mooring chain 26 is connected to the median part 34, advantageously at a certain depth L7 with respect to an upper part 60 of the anchor structure, for example to the plate 48.
The depth L7 is advantageously comprised between 40% and 75% of the depth L3, and is for example approximately half of the depth L3.
The second mooring chain 28 has a portion 62 in the second trench portion 21 , on the other side of the portion 58 of the mooring chain 26 with respect to the anchor structure 22, the second platform 13 applying a second traction force F2 on the anchor structure transversely.
The grout 24 aims at ensuring a sealing of the anchor structure 22 with the surrounding seabed 14, at least with the transverse wall 25. Advantageously, the grout 24 is located between the first wall 44 of the anchor structure 22 and the transverse wall 25, and advantageously between the second wall 56 of the anchor structure and a transverse wall 64 of the first trench portion 20 opposite the transverse wall 25. In the example, the grout 24 fully surrounds the anchor structure 22.
The grout 24 is for example a Portland grout and is adapted for curing underwater.
The grout 24 advantageously fills the first trench portion 20 up to seabed level over at least 90% of the anchor structure 22 along the line L. Advantageously, the grout 24 is adapted to develop a shear friction against the first trench portion 20 rocky walls of as a minimum 100 kPa.
A process of anchoring the floating platform 12 on the seabed 14, using the anchoring system 10, will now be described with reference to Figures 5 and 6.
Optionally, as shown in Figure 5, the seabed 14 is first surveyed for example by a remotely operated vehicle 66. Goal is to detect possible obstacles which could cause issues with the installation. One may also rely on previous knowledge of the seabed 14 such as bathymetry and seabed imagery.
Then the first trench portion 20 and the second trench portion 21 are provided in the seabed 14. For example, as shown in Figure 6, the first trench portion 20 and the second trench portion 21 are dug using a subsea trencher 68 commonly used for pipeline or cables burial.
The remotely operated vehicle 66 and the subsea trencher 68 are equipment known in themselves and available from the market.
As a variant, for example in case of a rough seabed 14 with some benches, the first trench portion 20 and/or the second trench portion 21 are existing one(s), and do not have to be dug.
Optionally, the first trench portion 20 and is cleaned, advantageously using water jets (not shown) directed at the walls 25, 64 of the first trench portion 20. The jets are for example produced by the remotely operated vehicle 66.
Then, the anchor structure 22 is installed, for example pre-assembled and lowered, in the first trench portion 20.
The mooring chain 26, and in the example the second mooring chain 28, are attached to the median part 31 of the anchor structure 22.
Afterwards, grout is injected in the first trench portion 20 at least between the anchor structure 22 and the transverse wall 25, in the example via the grout line 42 from a source (not shown), in order to obtain the grout 24.
As a variant (not shown), grout is injected using a stinger (not shown).
Advantageously, grouting is stopped when the first trench portion 20 is full of grout, or at least when the anchor structure 22 is surrounded by grout.
After curing, the mooring chain 26 is connected to the floating platform 12, and is tensioned. In the example, the same is performed with the second mooring chain 28 and the second floating platform 13.
The floating platforms 12, 13 may exert the traction forces F, F2 on the anchor structure 22 within a reasonable angle with respect to the transverse direction T. Thanks to the above features, the anchoring process is adapted to the rocky seabed 14 and preferably catenary mooring solutions, and allows reducing costs and the environmental footprint.
Design is fast. Limited soil investigation, for example over the top 3m of the seabed 14, is enough. All pieces of equipment are available in the market and easy to procure. The final assembly of the anchoring assembly 10 can be done locally. Installation is fast and requires only a dynamic positioning vessel. No pretension is needed.
The anchoring process advantageously allows anchoring several floating platforms.

Claims

1. A process of anchoring a floating platform (12) on a rocky seabed (14), comprising the following steps:
- providing a first trench portion (20) and a second trench portion (21 ) in the seabed (14), the first trench portion (20) extending along a line (L), and the second trench portion (21) extending from the line (L) in a transverse direction (T),
- installing an anchor structure (22) in the first trench portion (20), the anchor structure (22) comprising a median part (34) located at a junction (36) of the first trench portion (20) and the second trench portion (21), and two lateral parts (38, 40) extending from the median part (34) along the line (L) respectively on either sides of the median part (34), the median part (34) comprising more steel than the lateral parts (38, 40) per unit of length along the line (L),
- attaching a mooring steel chain (26) on the median part (34), on a side facing the second trench portion (21 ) along the transverse direction (T),
- injecting grout (24) in the first trench portion (20), at least between the anchor structure (22) and a transverse wall (25) of the first trench portion (20), and
- after curing of the injected grout (24), connecting the mooring chain (26) to the floating platform (12), the mooring chain having a portion (58) in the second trench portion (21), the floating platform (12) being intended to apply a traction force (F) on the anchor structure (22) transversely from the first trench portion (20) toward the second trench portion (21).
2. The process according to claim 1 , wherein providing the first trench portion (20) and the second trench portion (21) includes digging the seabed (14) along the line (L) and along the transverse direction using a subsea trencher (68).
3. The process according to claim 1 or 2, wherein the line (L) is straight.
4. The process according to any one of claims 1 to 3, wherein injecting the grout (24) includes using at least one grout line (42) of the anchor structure (22), said grout line (42) extending along the line (L), and/or using at least one stinger in order to inject at least part of the grout (24).
5. The process according to any one of claims 1 to 4, wherein the median part (34) comprises several steel plates (46) approximately parallel to the transverse direction (T).
6. The process according to claim 5, wherein the median part (34) comprises a first plurality (46A) of at least three plates parallel to each other, and a second plurality (46B) of at least three plates parallel to each, perpendicular to the plates of the first plurality (46A), and connecting the plates of the of the first plurality (46A) one with the other.
7. The process according to any one of claims 1 to 6, wherein the median part (34) forms a boxed area (50).
8. The process according to any one of claims 1 to 7, wherein the median part (34) comprises a plate (48) protruding transversely on which the mooring chain (26) is attached.
9. The process according to any one of claims 1 to 8, wherein each of the two lateral parts (38, 40) comprises a reinforcement cage fixed to the median part (34), the injected grout (24) at least partly filling the reinforcement cage of the two lateral parts (38, 40).
10. The process according to any one of claims 1 to 8, wherein:
- the anchor structure (22) comprises a first wall (44) extending along the line (L) and approximately perpendicular to the transverse direction (T), the first wall (44) forming part of the median part (34), and of the two lateral parts (38, 40), and
- the two lateral parts (38, 40) respectively comprise a first sheet (52) and a second sheet (54) extending along the line (L) and approximately perpendicular to the first wall (44), the first sheet (52) and the third wall (54) protruding transversely from the first wall (44) opposite said transverse wall (25).
11. The process according to claim 10, wherein the first wall (44) and the first sheet (52), and the first wall (44) and the second sheet (54) form “T” profiles.
12. The process according to claim 10 or 11 , wherein the anchor structure (22) comprises a second wall (56) extending along the line (L) and approximately perpendicular to the transverse direction (T), the second wall (56) forming part of the median part (34) and of the two lateral parts (38, 40), the first sheet (52) and the second sheet (54) being fixed to the second wall (56).
13. The process according to claim 12, wherein the grout (24) is also injected between the second wall (56) and another transverse wall (64) of the first trench portion (20) opposite said transverse wall (25) in the transverse direction (T).
14. The process according to any one of claims 1 to 13, further comprising:
- connecting a second mooring steel chain (28) to the median part (34), and
- after curing of the injected grout (24), connecting the second mooring chain (28) to a second floating platform (13), the second mooring chain having a portion (62) in the second trench portion (21 ), on the other side of the portion (58) of the mooring chain (26) with respect to the anchor structure (22), the second floating platform (13) being intended to apply a second traction force (F2) on the anchor structure (22) transversely.
15. An anchoring system (10) adapted for anchoring a floating platform (12) on a rocky seabed (14), the anchoring system (10) comprising:
- at least a first trench portion (20) and a second trench portion (21) located in the seabed (14), the first trench portion (20) extending along a line (L), and the second trench portion (21) extending from the line (L) in a transverse direction (T),
- an anchor structure (22) at least partly located in the first trench portion (20), the anchor structure (22) comprising a median part (34) located at a junction (36) of the first trench portion (20) and the second trench portion (21), and two lateral parts (38, 40) extending from the median part (34) along the line (L) respectively on either sides of the median part (34), the median part (34) comprising more steel than the two lateral parts (38, 40) per unit of length along the line (L),
- grout (24) located in the first trench portion (20), at least between the anchor structure (22) and a transverse wall (25) of the first trench portion (20), and
- a mooring steel chain (26) attached on the median part (34), on a side facing the second trench portion (21 ) along the transverse direction (T), the mooring chain having a portion (58) in the second trench portion (21) and being intended to be connected to the floating platform (12), the floating platform (12) being intended to apply a traction force (F) on the anchor structure (22) transversely from the first trench portion (20) toward the second trench portion (21 ).
PCT/EP2023/083187 2022-11-28 2023-11-27 Process of anchoring a floating platform on a rocky seabed WO2024115397A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP22306748 2022-11-28
EP22306748.9 2022-11-28

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090020065A1 (en) * 2007-07-16 2009-01-22 Petroleo Brasileiro S.A. - Petrobras Deep water high capacity anchoring system and method of operation thereof
US20140161538A1 (en) * 2012-12-12 2014-06-12 Dallas Joel Meggitt System and method for undersea micropile deployment
US10870965B2 (en) * 2018-08-30 2020-12-22 Exxonmobil Upstream Research Company Mat incorporated pile anchor reinforcement systems
WO2022018147A1 (en) * 2020-07-22 2022-01-27 Technip France Method for installing at least one mooring line of a floating installation in a body of water and associated floating installation

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090020065A1 (en) * 2007-07-16 2009-01-22 Petroleo Brasileiro S.A. - Petrobras Deep water high capacity anchoring system and method of operation thereof
US20140161538A1 (en) * 2012-12-12 2014-06-12 Dallas Joel Meggitt System and method for undersea micropile deployment
US10870965B2 (en) * 2018-08-30 2020-12-22 Exxonmobil Upstream Research Company Mat incorporated pile anchor reinforcement systems
WO2022018147A1 (en) * 2020-07-22 2022-01-27 Technip France Method for installing at least one mooring line of a floating installation in a body of water and associated floating installation

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