EP2860314B1 - Gravity foundation - Google Patents

Description

The invention relates to a method for gravity foundation of an offshore facility by lowering and an offshore facility and a barge as a floating body for performing the method.

Various methods for gravity foundation of structures under water have been known since ancient times in the art and have been constantly evolving. Gravity foundations are either built directly on the seabed towards the water surface with the help of a cofferdam or floating, for example by means of a caisson or caisson, with the help of overpressure, from the water surface towards the seabed or built on land, transported to location, and on the Lowered seabed.

As a method for lowering today various technologies are used: By building a foundation body within a caisson, by discharging stacked ring boxes or by means of controlled ballasting prefabricated structures

The lighthouse "Roter Sand" was founded by means of a caisson as the first offshore structure and completed in 1885.

In 1994, the founding structure of the Troll A platform was completed. The construction consists of a 36m high, built in a dock base dome, which was completed floating in a Norwegian fjord by means of a slipforming process to 3 total of 343 meters long basic columns. The structure was completely re-floated for transport and then towed to location and lowered there controlled by Ballastung.

The platform Hanze F2A was built in 2000 as a box-shaped steel construction on land, pulled to location in the Hanze field and founded by controlled lowering by ballasting in the North Sea.

In 2002, the buoyant foundation structure NAM F3 with tanks and columns was pulled to location in the North Sea, and the foundation structure was lowered in a controlled manner using ballast tanks.

A disadvantage of the known method for installation by gravity foundations by lowering by ballasting is that these methods are complex and involve great risks for stability during lowering. There are constructive compartments, buoyancy, pipes, valves, pumps and other associated temporary facilities on accompanying vessels necessary. The process itself must be carried out taking into account a very short and therefore complicated sequential hydrostatic stability to be determined.

From the DE 10 2008 017 785 A1 are a foundation for an offshore structure and a method for creating a foundation of an offshore structure known. The foundation is held laterally by means of a crane construction on a barge and lowered laterally next to the barge. The arrangement of foundation and barge is not very stable and susceptible to external forces, such as by waves.

It is therefore an object of the invention to provide a method of the type mentioned above, which allows the easier establishment of an offshore construction facility and to provide an arrangement of barge and offshore facility for carrying out the method.

The object is achieved in its first aspect by an initially mentioned method with the features of claim 1.

The offshore facility is kept in a dock. Conveniently, it is placed on a floor of the dock and is kept there. A barge is connected to at least one lowering means with the offshore facility. The offshore facility comprises a foundation body on which the offshore facility, after gravity formation, stands with its full weight and in contact with the seabed.

Preferably, otherwise, no component of the offshore facility has contact with the seabed after the foundation of gravity. Under a barge here is very generally a load-bearing ship or a suitably shaped float to understand. The arrangement of offshore facility and barge becomes buoyant. The arrangement is floated and spent from the dock on location. In the arrangement of the foundation body sea bottom side of the barge is arranged. The offshore facility can be operated by means of the at least one Absenkmittels be pulled up to the barge, and the foundation body is preferably kept sea bottom side of their hull.

At location, the offshore facility is stably lowered to a preferably pre-prepared area of seabed and established by gravity.

Preferably, the offshore facility is kept substantially ready in the dock. It is conveniently not buoyant by itself. Floating is only the arrangement of barge and offshore facility. The barge is used during the transfer the offshore facility as a means of transport and floats for the offshore facility.

The inventive method makes use of the idea of having an offshore facility with its foundation structure in a dock. The offshore facility is essentially already fully assembled. For example, it may already have a foundation structure with a foundation body and the essentially complete platform arrangement in the dock. It is connected without further structural changes by means of a lowering system installed on a barge with the barge and lowered stable to location. To lower only the lowering system is necessary. In addition, temporary facilities such as constructive compartments, buoys, pipes, valves, pumps are not needed for stable lowering. On location, the offshore facility is lowered with the help of at least one lowering device to the seabed, without causing the structural arrangement of the individual components of the offshore facility to each other must be changed.

In a preferred embodiment of the method according to the invention, the offshore device is kept ready in a flooded dock and moved up the barge in the dock to the offshore facility and then let water out of the dock and the barge connected to the offshore facility by the lowering device.

The development according to the invention makes use of the use of conventional docks, wherein the offshore device can first be mounted in a dry dock, as far as until the offshore device can be moved to establish a gravitational force. The dock can then be flooded so that the barge can enter the flooded dock by opening dock doors and then connecting to the offshore facility and then to the offshore facility via the lowering means.

Conveniently, after the barge has approached the offshore facility, the dock gates are closed again, the dock with the barge and the offshore facility drained, so that the barge sinks with the sinking water level in the dock. Conveniently, the offshore facility has a widened foundation body. In addition to the foundation body dock blocks are provided in a development of the invention, which have a dockbodenabseitige, flat bearing surface. Also, the foundation body of the offshore device on a dock floor side, flat bearing surface.

The bearing surfaces of the docking blocks and the foundation body are advantageously aligned with each other, so that the sinking barge, which also has a flat flat underwater surface conveniently rests stable on the dock blocks and the foundation body. Alternatively, the dock is not completely emptied, but the water level lowered so far that the barge rests with a part of its hull on the foundation body and otherwise still floats in the water.

The barge, which is lowered onto the foundation body and the dock blocks, is conveniently connected via the lowering means to the foundation body of the offshore installation in the dry dock. Preferably, an offshore side portion of the barge hull is provided with a fender to cushion the impact of the at least one offshore support with the barge on relative horizontal movement.

Preferably, the offshore facility itself is not buoyant. Floating is the arrangement of barge and associated with the barge offshore facility. Advantageously, the offshore device can be lowered to location by the action of gravity. It is not necessary to provide the offshore facility with ballast to allow for lowering. The weight force is greater than the largest buoyancy force acting during the entire lowering process.

In another variant of the method according to the invention, an already independently floatable offshore facility is kept ready. The offshore device is filled during lowering with ballast, especially seawater, so that the weight is greater than the respective buoyant force at any time and at any subsidence.

As a lowering means in a particularly preferred embodiment of the invention stranded joint systems are used, along the barge two rows of Litzenhebern are provided along the foundation body and two rows of fasteners for strands are provided, each one Litzenheber corresponds to one of the fasteners and through each of the strand jacks a strand is guided, one end of which is firmly and stably connected under tensile loads on the fastening device with the foundation body. The strands have a minimum length when the barge rests on the support surface of the foundation body. The strands are firmly locked with the strand lifters. Subsequently, the dock is flooded again. The barge and the offshore platform are dimensioned so that the buoyancy of the Barge is sufficient to lift the barge and the offshore platform firmly connected to it via the stranded-wire systems.

The lowering means may also be a crane or a crane-like device.

Preferably, individual ballast cells of the barge can be filled with seawater to counterbalance the offshore platform so that the barge and offshore platform arrangement is substantially horizontal in the water.

In a further development of the method, the barge is moved with connected and raised offshore platform floating from the dock and placed on location. There is conveniently prepared an area of the seabed. The offshore platform is moved exactly horizontally across the area by means of the barge and the offshore platform is then lowered by means of the stranded lifter system so that a seabed side of the foundation body rests on the area. The offshore facility is gravitational. After the foundation of gravity, a region of the seabed surrounding the foundation body and previously excavated may be backfilled. It is conceivable that the seabed is additionally covered after being backfilled with layers which prevent solid outgrowth.

In principle, other developments of the method are also conceivable. Depending on local conditions, the seabed in particular need not necessarily be prepared. It is also conceivable that the foundation body is lowered to a base frame, which was previously embedded in the seabed.

The process in reverse order of the above-mentioned process steps can also be carried out for the dismantling of an offshore facility. In this case, the barge is moved over the foundation body of the offshore device, with the at least one lowering device connected to the foundation body and the foundation body is preferably freed during lifting or temporally directly before the lifting of ballast and the offshore device is raised.

In the second aspect, the object is achieved by an arrangement of an offshore facility and a barge with the features of claim 6. The arrangement of offshore facility and barge is suitable for carrying out one of the said methods.

The inventive offshore device comprises a foundation body and at least one support between the foundation body and a structure, in particular a platform arrangement. The at least one support is preferably arranged eccentrically with respect to the foundation body, and a center of gravity of the offshore device is preferably horizontal, laterally spaced the at least one support between the foundation body and the support, and the barge and offshore equipment are connectable to each other by lowering means , An offshore facility can be understood to mean oil production platforms, lighthouses, wind turbine foundations, and so on.

Conveniently, the offshore facility in the dock is already substantially fully assembled. The offshore facility, towed out of the dock and founded, is essentially already operational. For their complete completion are no floating cranes o.Ä. necessary.

Preferably, the foundation body of the offshore facility is along the vertical extent of the arrangement sea bottom side of the barge and the structure meeresbodenabseitig the barge. A length of the at least one support is dimensioned such that the construction of the offshore facility fully lowered to location is arranged during and immediately after lowering meeresbodenabseitig the barge, so does not collide with the barge.

The offshore facility is designed eccentrically according to the invention. It is eccentric with respect to a virtual vertical axis guided by the center of gravity of the offshore platform. The at least one pillar, preferably each of the pillars, preferably the one pillar, lies completely outside the virtual vertical axis. The axis thus does not cut the support.

The offshore device is advantageously formed in a cross section through the at least one support and the foundation body is substantially L-shaped.

The offshore device is preferably dimensionally stable in its outer overall shape.

According to the invention, the offshore device is designed such that its center of gravity is arranged outside an imaginary outer shell of the offshore platform, next to the at least one support and between the foundation body and the platform arrangement such that the barge, when the barge with the offshore platform is firmly connected by lowering means and the offshore facility is raised, the center of gravity of the entire arrangement of barge and offshore facility is conveniently located within the outer vertical boundaries of the barge.

In a preferred embodiment of the invention, the lowering means comprise a stranded-wire jack system, wherein stranded jacks are provided on the barge and fastening means running on one outer wall and one strand each is guided through one of the strand jacks and with one end on the fastening device even under pressure. and tensile loads is firmly connected. The stranded-wire system makes it possible to lower and, if necessary, raise the offshore equipment again.

In addition to the lowering, preferably the Litzenhebersystem, no further temporary facilities such as structural Kompartiments, buoyancy, pipes, valves, pumps are necessary to lower the offshore facility stable.

In a further embodiment of the invention, the offshore facility itself is buoyant. For stable lowering tanks are provided in the offshore facility, which constantly increase the weight during the lowering process, thus allowing a stable lowering.

The offshore facility alone is preferably not buoyant. It is therefore reasonably settable by gravity without further ballasting. The arrangement of offshore facility and barge is of course buoyant.

Fig. 1

eine in einen Dock fahrende Barge mit einer Offshore-Plattform,

Fig. 2

ein geschlossenes und trockengelegtes Dock mit der Barge und mit der über ein Lizenzhebersystem verbundenen Offshore-Plattform,

Fig. 3

das geflutete Dock mit der angehobenen Offshore-Plattform, die aus dem gefluteten Dock mittels einer Barge gefahren wird,

Fig. 4

die Barge mit angehobener Offshore-Plattform während der Verbringung auf Lokation,

Fig. 5

die oberhalb eines vorbereiteten Bereichs des Meeresbodens positionierte Offshore-Plattform,

Fig. 6

das Absenken der Offshore-Plattform auf den vorbereiteten Bereich des Meeresbodens,

Fig. 7

die auf den Meeresboden abgesenkte Offshore-Plattform und sich entfernende Barge,

Fig. 8

eine schematische seitliche Ansicht einer erfindungsgemäßen Offshore-Plattform.

The invention will be described with reference to an embodiment in eight figures, in which:

Fig. 1

a docking barge with an offshore platform,

Fig. 2

a closed and dry dock with the barge and the offshore platform connected via a license lifter system;

Fig. 3

the flooded dock with the raised offshore platform being driven out of the flooded dock by means of a barge,

Fig. 4

the barge with raised offshore platform during shipment to location,

Fig. 5

the offshore platform positioned above a prepared area of the seabed,

Fig. 6

lowering the offshore platform to the prepared area of the seabed,

Fig. 7

the offshore platform lowered to the seabed and barge moving away,

Fig. 8

a schematic side view of an offshore platform according to the invention.

The FIGS. 1 to 7 show a method according to the invention by an offshore platform 1 of the invention by means of a barge 2 from a dock 3 spent on location and founded there by means of gravity foundation.

Fig. 1 shows partially in a sectional view and in a perspective view of the flooded dock 3 with the mounted offshore platform 1, which has a foundation body 4, a monopile 5 and a platform assembly 6. At a dock gate 7 facing the end of the foundation body 4 Dockblocks 8 are provided which have a height above a Dockbodens, which corresponds to a height of the foundation body 4 above the Dockbodens. Level, Dockbodenabseitige support surfaces 8a of Dockblocks 8 and a dockbodenabseitige support surface 4a of the foundation body 4 are aligned with each other and form a non-contiguous flat support surface for the barge 2 from.

Fig. 1 shows the barge 2 entering the flooded dock 3 from the sea through the dock gate 7 (not shown). The barge 2 has tanks that can be filled, for example, with seawater to create counterweights for the further process.

Fig. 2 shows the dock 3 with the dock dock closed 7 and in the drained state. The seawater is pumped out of the dock 3. The barge 2 is moved exactly above the Dockblocks 8 and the foundation body 4 before draining the dock 3. During the draining of the dock, the sea water level in the dock 3 gradually lowers, and the barge 2 sits on the bearing surfaces 8a of the dock blocks 8 and Support surface 4a of the foundation body 4 with its shallow underwater side. The barge 2 rests on the dock blocks 8 and the foundation body 4 stable.

At one of the offshore platform 1 facing end of the barge 2 stranded jacks 20 are provided. On the foundation body 4 of the offshore platform 1 fastening devices 21 are arranged for strands 22. On the fastening devices 21 one end of a strand 22 is attached, the other end is guided by an associated strand jacks 20. In Fig. 2 For example, the strands 22 between strand lifters 20 and fasteners 21 are shortened to a minimum length such that the offshore platform 1 is fixedly and relatively immovably connected to the barge 2.

Fig. 3 shows the dock 3 in Fig. 2 in the flooded state. However, the barge 2 and the offshore platform 1 are firmly connected to each other by means of the Litzenhebersysteme 20, 21, 22. During lifting by flooding of the dock 3, the tanks of the barge 2 are loaded sequentially, so that the barge 2 is substantially horizontal in the water even after raising the offshore platform 1.

Due to the flooding of the dock 3, the barge 2 experiences a sufficiently large lift that lifts the barge 2 including the associated offshore platform 1 from the dock floor. The dock 3 is flooded so far that the offshore platform 1 is positioned with a lower base side above the sea-top bearing surfaces 8a of the dock blocks 8, so that the barge 2 with the raised offshore platform 1 on the dock blocks 8 and moved out of the dock 3 on the sea is spent.

Fig. 4 shows the offshore platform 1 raised with the barge 2 shortly before the location. At the location, an area 40 of the seabed is prepared, so that the offshore platform 1 lowered there stands stable on the area 40 and the monopile 5 receives a vertical orientation.

Fig. 5 shows the barge 2 with the raised offshore platform 1 directly on location. The foundation body 4 of the offshore platform 1 is arranged directly above the area 40.

Fig. 6 Figure 3 shows the lowering operation of the offshore platform 1. The strand jacks 20 are released and the offshore platform 1 is lowered slowly and carefully onto the pre-prepared area 40 of the seabed by extending the strands 22. The monopile 5 is guided along the barge 2 by means of a guide, not shown.

The Fig. 7 shows the lowered to the area 40 offshore platform 1. A excavated the base body 4 excavated seabed area is backfilled, so that the foundation body 4 is secured against scouring or scouring. The strands 22 are released from the foundation body 4 and then lifted with the strand lift 20, and the barge 2 can be moved with strands 22 and strand lifters 20 to another offshore platform.

Fig. 8 shows the offshore platform 1 of FIGS. 1 to 7 in a detailed side view. In contrast to Fig. 7 the foundation body 4 of the offshore platform 1 is completely buried in the refilled seabed. The monopile 5 is not arranged symmetrically or centrically on the foundation body 4, but provided clearly on an outer edge of the foundation body 4 from an axis of symmetry. The foundation body 4 has a substantially cuboidal shape. At the grundkörperabseitigen end of the monopile 5, a platform assembly 6 is provided with three decks: one the foundation body 4 farthest weather deck 80 with other structures, a arranged between the weather deck 80 and the foundation body 4 basement deck 81 and a grundkörperseitig the basement decks 81 sludge deck 82nd wherein the mud deck 82 has a height above the sea level 83 which is still located above the maximum wave height. In the region of the sea level 83, 5 landing devices 85 for trusting supply boats are provided on the monopile.

Before lowering the offshore platform 1, the area 40 of the seabed is pre-prepared for location. For this, the area 40 is excavated and the bottom of the excavation is filled with a gravel layer 86. On the gravel layer, a foundation layer 87 is applied, on which the lowered foundation body 4 rests. The area of the excavation surrounding the foundation body 4 is backfilled with sand 88 so far that the foundation body 4 is completely covered with sand 88. On the sea level side, two further layers (not shown) may preferably be applied to the backfilled sand 88 to prevent scumming. On the foundation body 4, the fastening devices 21 are not shown, which make it possible to secure the lowered of the Barge 2 strands 22 on the foundation body 4 fixed position. The fastening devices 21 are dimensioned such that the offshore platform 1 with foundation body 4, monopile 5 and platform assembly 6 can be lifted by means of the strand jacks 20 of the barge 2.

LIST OF REFERENCE NUMBERS

1

Offshore platform

2

Barge

3

dock

4

foundation body

4a

bearing surface

5

monopile

6

platform assembly

7

Dock Gate

8th

Dockblocks

8a

support surfaces

20

strandjack

21

fasteners

22

strands

40

Area of the seabed

80

weather deck

81

cellar deck

82

mud deck

83

Height above sea level

85

landing facilities

86

gravel layer

87

foundation layer

88

sand

Claims (10)

1. A method for the gravity foundation of an offshore device (1) with a foundation body (4), by
   the offshore device (1) being kept ready in a dock (3) and
   a barge (2) being connected to the offshore device (1) by lowering means (20, 21, 22) and
   the foundation block (4) being arranged on the side of the barge (2) towards the seabed, and
   an arrangement comprising the barge (2) and the offshore device (1) becoming buoyant and
   the arrangement comprising the barge (2) and the offshore device (1) being moved out of the dock (3) to the site and
   the offshore device (1) being lowered onto a region of the seabed (40) at the site in a stable manner and
   the lowered offshore device (1) standing on the foundation block (4), characterized in that the barge (2) is moved vertically above a portion of the foundation block (4) of the offshore device (1) and is lowered onto the foundation block (4).
2. A method according to Claim 1, characterized in that the offshore device (1) is lowered in a stable manner onto the seabed only with the aid of the lowering means (20, 21, 22).
3. A method according to Claim 1 or 2, characterized in that the offshore device (1) is kept ready in the dock (3) flooded with water and the barge (2) in the dock (3) is brought up to the offshore device (1), and then the water is let out of the dock (3) and the barge (2) is connected to the offshore device (1) by at least one lowering device (20, 21, 22).
4. A method according to Claim 1, 2 or 3, characterized in that the barge (2) is connected to the offshore device (1) by means of at least one strand jack system (20, 21, 22) by which the offshore device (1) is lowered onto the region (40) of the seabed at the site.
5. A method according to any one of Claims 1 to 4, characterized in that dock blocks (8) are arranged adjacent to the foundation block (4), and the barge (2) is lowered and is set on flat support faces (8a) of the dock blocks (8) and at the same time on a flat support face (4a) of the foundation block (4).
6. An arrangement with an offshore device (1) and a barge (2) for carrying out a method according to any one of Claims 1 to 5,
   wherein the offshore device (1) comprises a foundation block (4) and at least one support (5) between the foundation block (4) and a platform arrangement (6) and
   at least one lowering device (20, 21, 22) and
   wherein the barge (2) and the offshore device (1) are connected to each other by means of the at least one lowering device (20, 21, 22) and the foundation block (4) is arranged on the side of the barge (2) towards the seabed,
   characterized in that the at least one support (5) is arranged eccentrically opposite the foundation block (4) and a centre of gravity of the offshore device (1) is arranged between the foundation block (4) and the platform arrangement (6) laterally distanced from the at least one support (5).
7. An arrangement according to Claim 6, characterized in that a common centre of gravity of the barge (2) and the offshore device (1) is arranged inside the outer vertical boundaries of the barge (2).
8. An arrangement according to Claim 6 or 7, characterized in that the at least one lifting device (20, 21, 22) each comprises one fastening apparatus (21) on the foundation block (4) each for one strand (22) and one strand jack (20) arranged on the barge (2).
9. An arrangement according to any one of Claims 6 to 8, characterized in that the at least one support is designed in the form of a monopile (5).
10. An arrangement according to any one of Claims 6 to 9, characterized in that the offshore device (1) is not buoyant on its own.

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