Gravity-Based Structure (GBS)

Abstract

The present invention is applicable to hydroelectric power plants and can be used to assemble production, transportation, transshipment and warehousing complexes for various applications in coastal and offshore locations. The GBS has rectangular top and bottom slabs 2, 4 and outer and inner vertical walls for separating it into compartments. The GBS has a central portion 1 and protruding portions 3. The central portion 1 of the GBS is shaped as a rectangular prism with said top slab 2. The GBS protruding portions 3 extend along both sides of the central portion 1 all around its periphery and have vertical outer walls 5. The protruding portions 3 and the central portion 1 share a bottom slab 4 and the protruding portion 3 is of lower height than the central portion 1. The central portion 1 has inner vertical longitudinal and transverse walls 5 forming compartments 6, 7 and the protruding portion 3 has inner vertical walls 5 perpendicular to its outer walls and forming compartments 15 from its short ends and forming ballast compartments 8 on both sides. Vertical longitudinal and lateral walls forming additional compartments 20 are located between the intermediate horizontal slab 13 and the bottom slab 4. The new GBS design is suitable for transportation through shallow water depths and adapted for arctic conditions and ice impacts.

Description

[Technical field]

[0001] The present invention is applicable to hydroelectric power plants and can be used to assemble production, transportation, transshipment and warehousing complexes for a variety of applications at onshore and offshore locations. [Background technology]

[0002] A gravity-based structure (GBS) is a platform that is fixed to the seabed with the help of its own weight. Gravity-based structures are used in near-shore and offshore waters, including icy conditions, where the water depth is sufficient to support very large structures whose required height exceeds the water level once the GBS is installed on the seabed. GBS are made of reinforced concrete and can be used as foundations for raw hydrocarbon production, storage, processing and transshipment equipment. Gravity-based structures can feature internal compartments to allow for their buoyancy during transportation to their installation site. GBS are designed to be floatable and have a ballasting system to allow for long-distance transportation and installation for operation at the intended offshore location without the use of costly lifting and transportation equipment.

[0003] There is a gravity-based structure for offshore LNG production, storage and offloading structure (KR20180051852A, publication date: 17 May 2018). The GBS is fabricated from steel and is installed on a sub-foundation prepared on the seabed near the shore with the help of solid ballast load. Once the GBS is installed on the seabed, the LNG processing equipment is installed on top of it. The GBS comprises an outer steel caisson in the form of a box with its lower face resting on a foundation prepared on the seabed near the shore, an inner steel caisson in the form of a box with an LNG storage space installed inside the outer caisson with the smallest possible gaps, a top deck installed on the outer steel caisson, walls made of waterproof insulating plates installed on the inner surface of the inner steel caisson and on the inner surface of the top deck to isolate the liquefied gas, liquefaction equipment and unloading equipment arranged on the top deck, and solid ballast filling the space between the outer and inner caisson to ensure the stability of the structure on the seabed due to gravity.

[0004] This design features the following drawbacks: 1. The GBS steel body is more susceptible to corrosion, which makes it less durable. 2. The GBS steel body needs to be significantly thicker to withstand the impact of ice, which means greater steel strength. 3. Solid ballast makes ballasting / deballasting operations of GBS more difficult. 4. The GBS is not protected against external influences such as ice impact or emergency ship impact. 5. The rectangular prism shaped GBS has a large draft when transported to the installation site, which makes transportation through shallow water areas impossible.

[0005] An offshore natural gas processing facility on a gravity-based structure (GBS) ( WO 2021 / 106151 A1 , publication date June 3, 2021 ) is known, which comprises a rectangular prism-shaped GBS having a bottom slab and a top slab, an intermediate slab with an internal vertical wall and on which one or more LNG tanks are arranged in a compartment, as well as a ballast compartment extending along the entire GBS, and an upper module mounted on and supported by the top slab.

[0006] Such GBS are characterized by the following drawbacks: - The rectangular prism-shaped GBS has a large draft when transported to the installation site, which makes transportation through shallow water areas impossible; - A long ballasting section runs along the entire length of the GBS without any lateral partitions, making GBS ballasting operations difficult; - the impossibility of using membrane tanks, which feature the lowest steel strength, in a row of LNG tanks in the same compartment; - The GBS is not protected against external influences such as ice impact or emergency ship impact.

[0007] The closest solution proposed is the Gravity Based Structure (GBS), a prismatic box-shaped concrete structure including top and bottom slabs, outer walls, inner longitudinal and transverse walls for separating the compartments, and an intermediate support slab for the tanks (Design and Construction on Gravity Based Structure and Modularized LNG Tanks for the Adriatic LNG Terminal. Lisa B. Waters et al. ExxonMobil Development Company. 2007. http: / / www.ivt.ntnu.no / ept / fag / tep4215 / innhold / LNG%20Conferences / 2007 / fscommand / PS6_7_Waters_s.pdf(file PS6_7_Waters_s).

[0008] Disadvantages of this GBS are also the fact that the prismatic shaped GBS has a large draft during transportation to the installation site making transportation through shallow water depths impossible, as well as the fact that the GBS is not protected from ice impact; to provide impact protection for emergency berthing the berthing arrangement would need to be moved away from the GBS outer wall in a truss structure. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] KR20180051852A [Patent Document 2] WO2021 / 106151A1 [Non-patent literature]

[0010] [Non-Patent Document 1] Design and Construction on Gravity Based Structure and Modularized LNG Tanks for the Adriatic LNG Terminal.Lisa B.Waters et al.ExxonMobil Development Company.2007.http: / / www.ivt.ntnu.no / ept / fag / tep4215 / innhold / LNG%20Conferences / 2007 / fscommand / PS6_7_Waters_s.pdf(file PS6_7_Waters_s) Summary of the Invention [Problem to be solved by the invention]

[0011] The technical problem solved by the invention is the following: Considering the growing share of production and infrastructure facilities in undeveloped areas, including coastal and offshore areas in the Arctic, there is an urgent need to develop new designs of gravity-based structures suitable for transportation at shallow water depths and adapted to operate underwater in ice conditions in the Arctic. [Means for solving the problem]

[0012] The proposed solution to the above problem is a Gravity Grounded Structure (GBS) having a rectangular bottom slab and a rectangular top slab and outer and inner vertical walls forming compartments, further according to the invention, the GBS has a central portion and a protruding portion, the central portion being a rectangular prism with said top slab, the protruding portion extending along both sides of the central portion all around its periphery and having outer and inner vertical walls forming ballast compartments on either side of the protruding portion, the protruding portion and the central portion sharing said bottom slab, the protruding portion being of lower height than the central portion.

[0013] A preferred design is characterized in that the GBS central portion has inner vertical longitudinal and lateral walls which form a compartment, and the inner vertical walls of the protruding portions are perpendicular to their outer walls and also form a compartment.

[0014] One more preferred design also features an internal intermediate horizontal slab of the GBS with vertical longitudinal and lateral walls that form an additional compartment between the intermediate horizontal slab and the bottom slab.

[0015] The technical results achieved by the proposed technical solution are as follows:

[0016] The GBS overhang not only adds buoyancy to the GBS and the entire structure, but also reduces its draft during transportation to the installation site.

[0017] The additional ballast sections at the periphery of the GBS within the overhanging portions aid in balancing the GBS, ie, allowing the GBS to settle to an even draft without roll and draft adjustment.

[0018] The increased width of the GBS base adds stability to the overall structure during its transportation and allows for upper structures of greater height and weight to be placed on the GBS.

[0019] The GBS projection also protects the centre section from ice impact and emergency ship impact.

[0020] The overhanging portion may also serve as a base for a pier. [Brief description of the drawings]

[0021] [Figure 1] FIG. 13 is a top view showing the integrated production complex on the GBS site. [Diagram 2] FIG. 2 is a cross-sectional view AA of FIG. [Diagram 3] FIG. 2 is a BB longitudinal cross-sectional view of FIG. [Figure 4] FIG. 2 is a CC longitudinal sectional view of FIG. [Diagram 5] FIG. 1 is a diagram of the layout of the GBS main compartment. [Figure 6] FIG. 3 is a diagram of the vertical wall arrangement in section DD with respect to FIG. 2. [Figure 7] FIG. 3 is a view of the vertical wall arrangement at section EE with respect to FIG. 2. [Figure 8] FIG. 13 is a diagram of the placement of the upper supports on the GBS top slab. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The GBS is assembled on a dedicated industrial site, where the upper part designed for production, transportation, transshipment or storage, as may be applicable depending on the intended use, is installed on the structure and then towed on the water surface to the installation site. The GBS is installed on a specific sub-foundation on the seabed. Gabions or other similar devices may be placed on the bottom around the GBS to prevent abrasive action on the foundations under the GBS and on the bottom of the water body. The GBS is installed near a dedicated quay and connected to the shore by flyovers and bridges, allowing the laying of access to the shore without the use of underwater pipelines and / or long overwater flyovers, allowing easy access to the production complex and quick evacuation of staff. The flyovers and bridges to reach the shore are installed after the GBS is installed at the operating site. Being located near the shore line, the GBS is integrated with the onshore facilities, including the hydrocarbon fields that are the source of feed materials for the production complex. Before the GBS is installed, the quay may be used to deliver cargo, for example for the development of hydrocarbon fields and the construction of onshore facilities.

[0023] The GBS is a three-dimensional structure made from reinforced concrete, which serves as a repository for extracted and processed feed materials, as well as for auxiliary substances and materials. It lies under the upper side of the production complex and is designed to be installed, with the help of its own weight, on the seabed 25 of a body of water. The central part 1 of the GBS is shaped as a rectangular prism and has a top slab 2 (Figure 1).

[0024] On either side of the central part 1 along the entire perimeter, GBS protruding parts 3 with vertical outer walls are arranged. The GBS central part 1 and the protruding parts 3 share the same bottom slab 4, and the height of the protruding parts 3 is lower than the height of the GBS central part 1 (Figures 2 to 4).

[0025] The GBS central portion 1 is separated into compartments by vertical longitudinal and lateral walls 5 (Figures 5-7). Some compartments, e.g. compartment 6, are used to store extracted and processed feedstock, while other compartments, e.g. compartment 7, are used to store ballast water. The GBS protruding portions 3 are separated into compartments by vertical walls 5 perpendicular to their outer walls, and compartment 8, located along the long side of the GBS, is also included in the ballast system.

[0026] The GBS top slab 2 has a reinforced concrete stool 9 on which the upper modules 10 are installed.

[0027] The GBS is able to remain afloat during water transportation to the site of the integrated production complex and is able to withstand ice impacts in icy waters. The change of state of the GBS from floating to stationary at the site of installation on the foundation 11 is ensured by the ballast compartments 7, 8 and 20, which are filled with water.

[0028] The GBS outer dimensions may vary depending on the purpose of the production complex, for example for an LNG plant, and the GBS dimensions (including the overhanging parts 3) may be as follows: length 324 m, width 154 m, height 30.2 m. In this case the length of the GBS central part 1 is 300 m, width 108 m and height 30.2 m. The overhanging parts 3 on both sides of the GBS have a width of 22 m and at the short end walls of the GBS it is 12 m. The height of the overhanging parts 3 is 13.75 m.

[0029] The main general arrangement solution of the GBS structure is defined by the scientific and technological parameters as well as the internal and external loads affecting the GBS structure, taking into account their maximum possible negative combinations.

[0030] The GBS central part 1 is of rectangular prism shape and includes the main support structure, i.e. the vertical longitudinal and transverse walls 5 and the horizontal slabs (top slab 2, bottom slab 4 and intermediate support slab 13 below the main tank 12 for storage of hydrocarbons and / or the respective processed products). The support structure ensures the necessary spatial rigidity of the frame of the GBS, including during transportation of the monolithic production complex and while it is floating until installation. The reinforced concrete walls also realize the division of the GBS into compartments according to their functional purpose. Some of the transverse walls 5, instead of being solid, may have a rectangular opening in their central part. In this case, they essentially fulfill the purpose of rigidity ribs.

[0031] The reinforced concrete wall also functions as a bearing structure transferring loads from the upper side 10 to the supporting slab 13 and foundation 11, so that the upper support 9 is located above the intersection of the vertical longitudinal and transverse walls 5 of the GBS.

[0032] The top slab 2 of the GBS is sloped from the central longitudinal line to the edges for drainage of atmospheric precipitation and process runoff. The structure of the top slab 2 is designed to withstand explosion loads in case of emergency situations. When cryogenic liquids are involved in the scientific and technological process, steel with enhanced cryogenic resistance characteristics is used as reinforcement to protect the top slab 2 from the runoff of the cryogenic medium.

[0033] A horizontal support slab 13 is provided between the top slab 2 and the bottom slab 4 to distribute the loads from the storage tanks 12 of liquid hydrocarbons and / or the respective processed products. Longitudinal and transverse walls 14 below this slab 13 transfer the loads to the bottom slab 4 and ensure the spatial rigidity of the structure.

[0034] Reinforced concrete, based on normal density concrete modified with tensioned reinforcement, is the main material of the central part 1 of the GBS.

[0035] The projections 3 are arranged along the periphery of the GBS central section 1 and form a unitary structure therewith. The long sides of the projections 3 mostly house the ballast sections 8 (FIG. 5) and the short end sides mostly house the auxiliary and engineering sections 15. The projections 3 of the GBS serve the following main purposes: - achieving the required target GBS buoyancy parameters; - to accommodate the ballast compartment 8 intended essentially to balance the GBS and ensure that it floats evenly without roll and draft adjustments; - forming a natural protective barrier in case of design emergency collision / ship impact, the protruding parts 3 absorbing and dissipating most of the impact energy, preventing damage to the main parts of the GBS frame and ensuring the integrity and maintenance of the supporting structure of the main tank 12 and upper foundation; - To accommodate auxiliary processing and shipboard equipment to ensure LNG carriers can moor and offload liquid hydrocarbons.

[0036] Storage tanks for liquid hydrocarbons and / or the respective processed products are housed in the GBS compartment and are intended for the storage of the products of the integrated production complex. Depending on its intended use, the production complex may also have storage tanks for feedstocks, semi-processed products and consumables. The GBS central part 1 has several tanks 12 (Fig. 5) that may have different designs depending on the properties of the substances to be stored. For unpressurized storage of LNG and cryogenic liquids, membrane tanks are used. In this case, the tanks 12 consist of a metal membrane made of stainless steel or Invar (Fe-Ni alloy), separated from the concrete structure by a thermal insulation layer installed inside the concrete compartment 6. The thermal insulation layer is placed directly on the top slab 2, the intermediate slab 13 and the walls of the GBS, transferring the load from the tank 12 and its liquid contents to the boundary structures listed above. The GBS slabs and walls thus serve as a support structure for the membrane tanks, with which they are integrated into a single structural unit. To prevent any leakage, the bottom and sides of the membrane tank 12 have a secondary barrier in the form of an additional membrane placed inside the insulating layer.

[0037] In the case of the LNG plant, the liquefied gas is stored in two 115,000 cbm tanks 12 each installed in an individual compartment 6 of 135 x 40 x 24 m. The compartment 6 with the tanks 12 is surrounded by a dry compartment 16 which allows inspection of the outer surface of the tank boundary structure.

[0038] For storage of condensate and other liquid hydrocarbons that do not require low temperatures, GBS concrete compartments 17 may be used, whose boundary structure acts as a protective barrier. Part of the compartments 7 can be used for both ballast water and storage of condensate and other liquid hydrocarbons that do not require maintaining low temperatures. In the case of an LNG plant, there is a compartment 7 of 135x30x30m with 75,000cbm for stable condensate storage, and one of the compartments 17, with a capacity of 5,000cbm and a size of 30x8x30m, is for substandard condensate storage.

[0039] "Wet" storage, including an underlying layer of water, may be used for hydrocarbons that are less dense than water. In this case, the bottom layer of stored product, around 1m thick, is considered as a mixing zone that ensures guaranteed separation of water and stored product during the loading operation. Compartment 7 is also slightly pressurized (from atmospheric levels) by utilizing a nitrogen blanket at the top of compartment 7 to prevent air ingress into compartment 7 and the formation of flammable and explosive gas mixtures with the hydrocarbon vapours.

[0040] The height of the underlying water layer in compartment 7 may be fixed or variable. In the case of a fixed water layer height, the height of the underlying water layer is fixed, for example fixed at 2 meters, regardless of the quality of the condensate or other liquid hydrocarbons stored in the compartment. Changes in the amount of condensate in compartment 7 are compensated by changing the amount of nitrogen blanket. In the case of a variable water layer height, the height of the underlying water layer is changed so that compartment 7 is permanently filled with liquid. When compartment 7 is filled with condensate or other liquid hydrocarbons, part of the water is removed from it by an active ballast system. When the level of stored hydrocarbons drops, additional water is supplied to compartment 7.

[0041] A compartment 6 for the storage of large volumes of hydrocarbons is located within the central portion 1 of the GBS. Smaller compartments such as tanks (e.g. for diesel fuel, hot oil or glycol solutions) may also be located within the protruding portions 3 of the GBS.

[0042] To store small volumes, self-supporting tanks are also used in the GBS compartment (in the central part 1 or in the protruding part 3). In the case of an LNG plant, self-supporting tanks are used for waste water, desalted water, fresh water, wash water, absorbents, butane and propane.

[0043] The auxiliary and engineering compartments 16 in the GBS central part 1 are located on either side of and centrally between the main hydrocarbon storage compartment 6. These compartments 16 are intended for processing needs, placement of equipment, tanks for processing fluids, as well as access and evacuation routes for staff. With the dry compartments 16 along the periphery of the main compartment 6 for hydrocarbon storage, the outer surface of the boundary walls of the tanks 12 for hydrocarbon storage can be inspected.

[0044] The auxiliary and engineering compartments 15 are located within the protruding portion 3 of the GBS. These compartments 15 are intended for the processing needs, the placement of equipment and tanks for processing fluids.

[0045] The support 9 of the upper side 10 on the top slab 2 of the GBS ensures the perception of the reaction of the support from the upper side 10 to the main load-bearing structure of the GBS. Structurally, the support is a reinforced concrete tower with heads for the embedded components. At the GBS support 9 and upper side 10 connection points, special sealing is used to compensate the thermal expansion of the upper side 10 by ensuring free rotation and movement in a given direction.

[0046] The location of the supports 9 on the layout (FIG. 8) is defined based on the intersection of the GBS load bearing walls 5 to ensure distribution of the load from the topside 10. A deck 24 supporting the topside 10 is installed on top of the supports 9.

[0047] The GBS ballast system includes an inner ballast compartment 7, an inner ballast compartment 20 below the support slab 13 formed by vertical walls 14, and an outer ballast compartment 8 located within the GBS central section 1 and the GBS protruding section 3. A ballast recirculation and heating system is provided to prevent freezing of water in the ballast compartments. The water in the ballast compartments is heated using waste heat from the exhaust gases of the gas turbine mounted on the upper side 10.

[0048] The ballast system serves two main functions, namely: - ballasting operations, i.e. changing the weight of the GBS to ensure the required GBS draft when floating and the structural stability of the GBS when installed on the sub-foundation; and - Balancing the GBS, i.e. making it even-drafted without roll or draft adjustments when floating, through compensation with ballast water for the structural centre of gravity deviation from its geometric centre.

[0049] A liquid hydrocarbon unloading pier 21 will be structurally integral with the GBS and the upper side. Fenders and unloading platforms with unloading arms and other vessel and processing equipment allowing the unloading of liquid hydrocarbons will be installed on the seaward side of the GBS in the overhanging section 3. Mooring equipment for carrier berthing will be installed on the seaward side of the upper side.

[0050] Pier 21 can also be used to unload liquid hydrocarbons from carriers. If the production complex on the GBS is a power generation facility, the main function of the pier is to receive LNG from gas carriers.

[0051] The layout of compartments within a GBS depends on its functional design, including the intended use of the integrated production complex. In general, a GBS is designed to have three types of compartments: ballast compartments, hydrocarbon storage compartments, auxiliary and engineering compartments.

[0052] In the case of a GBS LNG plant, the GBS central part 1 comprises six main compartments (Figure 5). Two compartments 6 along the GBS centreline are intended for the storage of hydrocarbons, while the four side compartments 7 can be used both as ballast compartments and as additional storage compartments for hydrocarbons, e.g. condensates. In the case of "wet" storage of hydrocarbons with variable water levels, the compartments 7 are both ballast compartments and storage compartments for hydrocarbons and / or the respective processed products. Auxiliary and engineering compartments 16 as well as additional hydrocarbon storage compartments 17 are located between the main compartments 6, 7.

[0053] An additional ballast section 20 (FIGS. 2 and 4) is disposed below the main hydrocarbon storage section 6 between the bottom slab 4 and the support slab 13 for the main hydrocarbon storage tanks 6,7.

[0054] The overhang 3 (Figure 5) houses a ballast section 8 and an auxiliary and engineering section 15. In the case of the GBS LNG plant, the overhang 3 on both sides comprises mostly the ballast section 8, while at the short end it comprises mostly the auxiliary and engineering section 15.

[0055] The compartments may be separated by lateral partitions, except for the main LNG storage compartment 6. In this case openings are made inside the ballast compartment to allow the ballast water to flow through, and passages for staff and the distribution of cabling and piping are made in the partitions of the auxiliary and engineering compartments.

[0056] The integral GBS is connected to the shore as required by two flyovers 22 in which the piping and cabling are laid, and three evacuation bridges 23 for staff movement and evacuation. The flyovers and bridges are made of steel and mounted on supports which stand on the GBS top slab 2 on the one hand and on the quayside 18 on the other hand. The seabed 25 and the water level 26 in the water body are shown in figures 2 to 4.

Claims

1. 1. A gravity-grounded structure having a rectangular bottom slab and a rectangular top slab, and outer and inner vertical walls forming a compartment, the structure having a central portion and a protruding portion, the central portion being a rectangular prism with the top slab, the protruding portion extending along either side of the central portion all around its periphery, the protruding portion having outer and inner vertical walls forming a ballast compartment on either side of the protruding portion, the protruding portion and the central portion sharing the bottom slab, and the protruding portion being of a lower height than the central portion.

2. 2. The gravity-landing structure of claim 1, wherein said central portion has inner vertical longitudinal and lateral walls forming a compartment, and the inner vertical walls of said protruding portions are perpendicular to their outer walls.

3. 2. The gravity-landed structure of claim 1, further comprising an intermediate horizontal slab having vertical longitudinal and lateral walls that form an additional compartment between the intermediate horizontal slab and the bottom slab.

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