Seabed anchoring device

Abstract

Device for anchoring in a seabed comprising a hollow cylinder comprisingan open upper base, an open lower base configured to be embedded in the seabed, a peripheral wall with an internal face and an external face, an internal stiffening structure attached to the internal face of the hollow cylinder and extending axially within the cylinder between the lower and upper bases of the cylinder, and an anchoring chain fastening means rigidly connected to the hollow cylinder.

Description

The present invention relates to a device for anchoring in a seabed, a floating structure secured to the seabed by means of said anchoring device, a system for placing the anchoring device in the seabed, and a method for anchoring the anchoring device using the placement system.

[0002] The floating structure is for example a platform floating on a body of water, which is intended for the production, recovery, treatment and / or storage of fluid, in particular hydrocarbons. Alternatively, the floating installation is a floating installation for producing renewable energy, in particular for producing wind or tidal power.

[0003] Installations of this type, comprising a surface assembly floating on a body of water, must generally be anchored in a robust manner to the bottom of the body of water. This prevents them from moving under the effect of the many external stresses to which they are subjected. These stresses include wind, waves, swell and / or sea currents.

[0004] The anchoring must be robust, even when the water depth is considerable. Anchoring is generally carried out by depositing anchoring lines at the bottom of the body of water, drawing the anchoring lines back up toward the surface assembly, then pulling the anchoring lines taut from the surface assembly.

[0005] Many anchoring systems exist; however, installing anchoring systems requires a lot of time to mobilize specialized ships.

[0006] The installation of the anchors also constitutes a significant part of the development risks associated with floating projects. Indeed, it is expensive and complex to carry out reconnaissance at sea, and often the geological and geotechnical risks cannot be completely identified or quantified. The installation phase therefore often comprises residual risks that can significantly increase the anchoring costs for a project.

[0007] It is therefore necessary for the offshore industry to have new anchoring device systems which make it possible to reduce both the production and usage costs of the anchorings, as well as the associated installation risks.

[0008] A solution of the present invention is a device 1 for anchoring in a seabed 8 comprising:

[0009] a hollow cylinder 2 comprising:

[0010] an open upper base 3,

[0011] an open lower base 4 configured to be embedded in the seabed,

[0012] a peripheral wall 5 with an internal face and an external face,

[0013] an internal stiffening structure 6 which is attached to the internal face of the hollow cylinder and extends axially within the cylinder between the lower and upper bases of the cylinder, and

[0014] an anchoring chain fastening means 9 which is rigidly connected to the hollow cylinder.

[0015] FIG. 1 is an example of an anchoring device according to the invention.

[0016] The term “seabed” is understood in the broad sense to include the bottom of all bodies of water, whether they are seas, oceans, lakes or rivers.

[0017] The stiffening structure makes it possible to increase the friction surface between the seabed and the anchoring device, thereby improving the anchoring and reducing the amount of space required for the anchoring device.

[0018] The device according to the invention may comprise one or more of the following features, considered alone or according to any technically possible combination:

[0019] the lower base of the cylinder communicates fluidically with the upper base of the cylinder via the internal volume of the cylinder;

[0020] the stiffening structure extends over at least 50% of the length of the cylinder, preferably over at least 70% of the length of the cylinder and more preferably over at least 90% of the length of the cylinder;

[0021] the stiffening structure has a cross-section in the shape of a cross, grid, star or spider's web;

[0022] the cylinder has a height of between 5 m and 25 m and a diameter of between 1 m and 5 m;

[0023] the cylinder and the stiffening structure comprise a selected material such as iron or aluminum, as well as any combination of at least one of these metals with another material such as chromium, nickel or titanium, for example;

[0024] the anchoring device weighs between 20 tonnes and 150 tonnes;

[0025] the anchoring chain fastening means is rigidly connected to the external face of the cylinder.

[0026] The present invention also relates to a floating structure secured to the seabed by means of at least one anchoring chain attached to at least one anchoring device according to the invention.

[0027] Advantageously, the anchoring chain comprises a first end attached to the floating structure and a second end attached to the anchoring chain fastening means of the anchoring device.

[0028] The floating structure preferably comprises a wind turbine.

[0029] The invention also relates to a system for placing an anchoring device according to the invention in a seabed, comprising a removable anchoring follower device 7 which comprises a bearing structure which is configured to engage with at least part of the internal stiffening structure of the anchoring device via the open upper base 3 of the cylinder 2, in order to allow the anchoring device to be pushed into the seabed 8 when the anchoring device 1 is placed in the seabed.

[0030] FIG. 2 is a schematic view of the anchoring follower device connected to the anchoring device.

[0031] The follower is simply placed on the anchoring device with a part that optionally penetrates the anchoring device in order to engage with at least part of the stiffening structure; however, clips or a clamping device could also be used to temporarily connect the two parts.

[0032] Depending on the circumstances, the system for placing an anchoring device comprises one or more of the following features:

[0033] the bearing structure of the anchoring follower device comprises an external cross-section which is smaller than the internal diameter of the cylinder;

[0034] the bearing structure is in the shape of a cross, parallelepiped, star or circle;

[0035] the bearing structure comprises a coating which makes it possible to reduce the stresses imposed during installation, for example paint, Teflon, etc.;

[0036] the removable anchoring follower device has a height of between 5 m and 20 m;

[0037] the anchoring follower device weighs between 20 tonnes and 150 tonnes, preferably less than 100 tonnes;

[0038] the system comprises a hammering device configured to hammer the removable anchoring follower device when its bearing structure engages with at least part of the internal stiffening structure of the anchoring device when the anchoring device is placed in the seabed.

[0039] Finally, the present invention relates to a method for anchoring an anchoring device, as defined above, in a seabed, by means of a placement system according to the invention, said method comprising the following steps:

[0040] a) submerging the anchoring device until it reaches the seabed,

[0041] b) submerging the anchoring follower device,

[0042] c) placing the anchoring follower device in such a way that the bearing structure of the anchoring follower device engages with at least part of the internal stiffening structure of the anchoring device,

[0043] d) hammering the anchoring device placed in step c) so as to embed the anchoring device at least partially in the seabed, and

[0044] e) disengaging the anchoring follower device from the anchoring device which is embedded at least partially in the seabed.

[0045] Preferably, the submersion step b) will be carried out by handling, with fastening means and the use of cranes or winches.

[0046] According to an advantageous embodiment, steps a) and b) are combined.

[0047] According to a further advantageous embodiment, step c) can be carried out before or after the submersion steps a) and b). Indeed, if the handling means are sufficient, the anchoring device and the follower device can be submerged simultaneously.

[0048] Preferably, the hammering can be carried out using a hammer or vibrating machine.

[0049] The method according to the invention can comprise a step of fastening an anchoring chain to the anchoring device. Preferably, the anchoring chain has a first end and a second end and the first end is attached to the fastening means of the anchoring device, the other end being configured to be attached to the floating structure.

[0050] This step of attaching the anchoring chain can be carried out before or after submersion of the anchoring device. If the anchoring chain is attached after submersion of the anchoring device, the first end of the anchoring chain will be attached to the fastening means of the anchoring device before or after the hammering step.

[0051] FIG. 3 to 6 show different geometries of the anchoring device and anchoring follower device according to the invention.

[0052] The left-hand side of FIG. 3 is a plan view of an anchoring device with a stiffening structure which has a cross-section in the shape of a cross and the right-hand side is the cross-section of the bearing structure of an anchoring follower device, in the shape of a cross. The cross-shaped stiffening structure makes it possible to increase the friction surface with respect to the seabed and thereby reduce the amount of space required for the anchoring device. The shape of the anchoring follower device, when compared with a cylindrical anchoring follower device with a diameter equal to the diameter of the anchoring device, allows for easier production, easier storage and requires less space.

[0053] The left-hand side of FIG. 4 is a plan view of an anchoring device with a stiffening structure which has a cross-section in the shape of a grid and the right-hand side is the cross-section of the bearing structure of an anchoring follower device in the form of a perforated square. In this instance, the bearing structure can be a tubular structure with a square or rectangular cross-section, which is optionally perforated. In the same way as before, the stiffening structure with a cross-section in the shape of a grid also makes it possible to reduce the space required for the anchoring device. The shape of the anchoring follower device, when compared with a cylindrical anchoring follower device with a diameter equal to the diameter of the anchoring device, allows for easier production. Moreover, perforating the structure of the anchoring follower device makes it possible to reduce the weight to be handled.

[0054] The left-hand side of FIG. 5 is a plan view of an anchoring device with a stiffening structure which has a cross-section in the shape of a “star” and the right-hand side is the cross-section of the bearing structure of an anchoring follower device which is also in the shape of a “star”, but without a central core. A star shape with a central core can also be envisaged for the cross-section of the bearing structure. The term “star” shaped is understood to be a star of which the branches correspond to radii of the same circle. In the same way as before, the stiffening structure with a cross-section in the shape of a star reduces the amount of space required for the anchoring device. The shape of the anchoring follower device, when compared with a cylindrical anchoring follower device with a diameter equal to the diameter of the anchoring device, allows for a better distribution of the forces exerted during the hammering, making the solution less susceptible to wear.

[0055] The left-hand side of FIG. 6 is a plan view of an anchoring device with a stiffening structure which has a cross-section comprising spokes or spoke portions, and circles or circle portions (2 alternatives are shown), and the right-hand side is the cross-section of the bearing structure of a circle-shaped anchoring follower device with a diameter smaller than the diameter of the cylinder of the anchoring device. In this case, the bearing structure can be a tubular structure with a circular cross-section which is optionally perforated (the two alternatives are shown). In the same way as before, the stiffening structure with a cross-section in the shape of a star reduces the amount of space required for the anchoring device. The shape of the anchoring follower device, when compared with a cylindrical anchoring follower device with a diameter equal to the diameter of the anchoring device, allows for a better distribution of the forces exerted during hammering, making the solution less susceptible to wear.

[0056] Regardless of the shape selected, the fact that the bearing structure of the anchoring follower device comprises an external cross-section which is smaller than the internal diameter of the cylinder reduces friction at the interface between the anchoring device and the follower device when the follower device is placed on the anchoring device. As a result, the hammering energy will be reduced, as well as the pulling force required to remove the follower.

[0057] In a general manner, the solution according to the invention has numerous advantages.

[0058] Firstly, the solution according to the invention has an advantage in terms of the carbon footprint. Indeed, the carbon footprint depends heavily on the quantities of steel used and on the transport. However, the proposed solution can be more compact because the force to weight ratio is significant, between 10 and 20. The dimensions of the anchoring device and of the follower device are effectively reduced and the amount of steel used is reduced by a factor of at least 1.5, preferably by at least 2.

[0059] Another advantage is that the risk related to the nature of the terrain is easily managed by adapting the depth of insertion of the foot of the chain according to the nature of the terrain encountered.

[0060] It suffices to provide a sufficiently long mooring chain and a sufficiently long follower in order to adapt the penetration depth according to the nature of the terrain. When the terrain is highly stratified, it is in fact easy to identify the different layers by measuring the penetration speeds and the number of hammer blows. It is not necessary to have a specific design for each location; it is sufficient to adapt the penetration depth of the chain in accordance with the nature of the terrain encountered. This advantage makes it possible to limit the need for investigation at each anchor location.

[0061] Moreover, the hammering has a significant environmental impact on marine mammals, since the noise can reach 220 dB. Anything which can limit the hammering energy allows noise pollution to be reduced. As explained above, the solution according to the invention makes it possible to reduce friction at the interface between the anchoring device and the follower device when the follower device is placed on the anchoring device. Therefore, the hammering energy is reduced, as well as the pulling force required to remove the follower. Adding a coating to the bearing structure of the follower device further reduces the energy required to hammer and to retrieve the follower device.

Claims

1. A device for anchoring in a seabed comprisinga hollow cylinder comprising:an open upper base,an open lower base configured to be embedded in the seabed,a peripheral wall with an internal face and an external face,an internal stiffening structure attached to the internal face of the hollow cylinder and extending axially within the cylinder between the lower and upper bases of said cylinder, the stiffening structure extending over at least 50% of the length of the cylinder, at least part of the stiffening structure being capable of engaging with a bearing structure of an anchoring follower device, andan anchoring chain fastening means rigidly connected to the hollow cylinder.

2. The device according to claim 1, characterized wherein the lower base of the cylinder communicates fluidically with the upper base of the cylinder via the internal volume of the cylinder.

3. The device according to claim 1, wherein the stiffening structure extends over at least 70% of the length of the cylinder, and preferably over at least 90% of the length of the cylinder.

4. The device according to claim 1, wherein the stiffening structure has a cross-section in the shape of a cross, grid, star or spider's web.

5. The device according to claim 1, wherein the cylinder has a height of between 5 m and 25 m and a diameter of between 1 m and 5 m.

6. The device according to claim 1, wherein the cylinder and the stiffening structure comprise a selected material such as iron or aluminum, as well as any combination of at least one of these metals with another material.

7. The device according to claim 1, wherein the anchoring chain fastening means is rigidly connected to the external face of the cylinder.

8. A floating structure secured to the seabed by means of at least one anchoring chain attached to at least one device defined in claim 1.

9. The floating structure according to claim 8, wherein the anchoring chain comprises a first end attached to the floating structure and a second end attached to the anchoring chain fastening means of said anchoring device.

10. The floating structure according to claim 8, wherein the floating device it comprises a wind turbine.

11. A system for placing an anchoring device in a seabed, comprising a removable anchoring follower device and an anchoring device, the anchoring device comprising the device recited in according to claim 1, the anchoring follower device comprising a bearing structure configured to engage with at least part of the internal stiffening structure of the anchoring device via the open upper base of said cylinder, in order to allow the anchoring device to be pushed into the seabed when the anchoring device is placed in the seabed.

12. The system according to claim 11, wherein the bearing structure of the anchoring follower device comprises an external cross-section that is smaller than the internal diameter of the cylinder.

13. The system according to claim 11, wherein the bearing structure is in the shape of a cross, parallelepiped, star or circle.

14. The system according to claim 11, wherein the bearing structure comprises a coating which makes it possible to reduce the stresses imposed during installation.

15. The system according to claim 11, wherein the removable anchoring follower device has a height of between 5 m and 20 m.

16. The system according to claim 11, wherein it comprises a hammering device configured to hammer the removable anchoring follower device when its bearing structure engages with at least part of the internal stiffening structure of the anchoring device when the anchoring device is placed in the seabed.

17. A method for anchoring the device recited in claim 1, in a seabed, by means of a placement system for placing an anchoring device in a seabed, comprising a removable anchoring follower device and an anchoring device, the anchoring device comprising the device, the anchoring follower device comprising a bearing structure configured to engage with at least part of the internal stiffening structure of the anchoring device via the open upper base of said cylinder, in order to allow the anchoring device to be pushed into the seabed when the anchoring device is placed in the seabed, said method comprising the following steps:a) submerging the anchoring device until it reaches the seabed,b) submerging the anchoring follower device,c) placing the anchoring follower device in such a way that the bearing structure of the anchoring follower device engages with at least part of the internal stiffening structure of the anchoring device,d) hammering the anchoring device placed in step c) so as to embed the anchoring device at least partially in the seabed, ande) disengaging the anchoring follower device from the anchoring device which is embedded at least partially in the seabed.

18. The anchoring method according to claim 17, wherein steps a) and b) are combined.

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