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 anchored 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 enable 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, published date: May 17, 2018). The GBS is made of steel and is installed on a sub-foundation prepared on the seabed near shore with the help of solid ballast loads. Once the GBS is installed on the seabed, the LNG processing equipment is installed on top of it. The GBS comprises a box-shaped outer steel caisson with its lower surface resting on a foundation prepared on the seabed near the shore, a box-shaped inner steel caisson with an LNG storage space installed inside the outer caisson with the smallest possible gap, 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 by gravity.

[0004] This design is characterized by 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 from 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) (WO2021 / 106151A1, 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 one or more LNG tanks arranged in a compartment thereon, a ballast compartment extending along the entire GBS, and an upper module installed on and supporting 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 it impossible to transport through shallow water areas; - The long ballasting section runs along the entire length of the GBS without any lateral partitions, making GBS ballasting operations difficult; - It is not possible to use membrane tanks, which feature the lowest steel strength, in a row of LNG tanks in the same compartment; - The GBS is not protected from external influences such as ice impacts or emergency ship impacts.

[0007] The closest solution to be 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 separating the tanks into 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 shape of the GBS has a large draft during transport to the installation site, making transport through shallow water 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: In view of 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 in 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-based structure (GBS) having a rectangular bottom slab and a rectangular top slab, and outer and inner vertical walls forming compartments, and further, according to the invention, the GBS has a central portion and protruding portions, the central portion being a rectangular prism with said top slab, the protruding portions extending along either side of the central portion all around its periphery and having outer and inner vertical walls forming ballast compartments on either side of the protruding portions, the protruding portions and the central portion sharing said bottom slab, and the protruding portions being of a lower height than the central portion.

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

[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 compartments at the periphery of the GBS inside the projections help balance the GBS, ie, allow the GBS to settle to an even draft without roll and draft adjustments.

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

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

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

[0021] [Figure 1] FIG. 1 is a top view showing the integrated production complex on the GBS deployment. [Figure 2] 2 is a cross-sectional view AA of FIG. 1. [Figure 3] FIG. 2 is a BB longitudinal cross-sectional view of FIG. [Figure 4] FIG. 2 is a CC longitudinal cross-sectional view of FIG. [Figure 5] FIG. 1 is a diagram of the layout of the GBS main compartment. [Figure 6] 3 is a view of the vertical wall arrangement in section DD with respect to FIG. 2. FIG. [Figure 7] 3 is a view of the vertical wall arrangement at section EE with respect to FIG. 2. FIG. [Figure 8] FIG. 10 is a diagram of the placement of the upper supports on the GBS top slab. DETAILED DESCRIPTION OF THE INVENTION

[0022] The GBS is assembled at a dedicated industrial site, where a topside designed for production, transportation, transshipment, or storage, as applicable depending on the intended use, is installed on the structure, which is then floated and towed 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 abrasion of the foundation below the GBS and the bottom of the water body. The GBS is installed near a dedicated quay and connected to shore by overpasses and bridges, allowing for the construction of access to shore without the use of underwater pipelines and / or long overwater overpasses, and allowing for easy access to the production complex and quick evacuation of staff. The overpasses and bridges to reach shore are installed after the GBS is installed at the operating site. By being located near the shoreline, the GBS is integrated with onshore facilities, including the hydrocarbon field that is the source of feedstock 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 that serves as a reservoir for extracted and processed feedstock, as well as for auxiliary substances and materials. It is located below the upper side of the production complex and is designed to rest on the seabed 25 of a body of water with the help of its own weight. 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 are arranged GBS protruding parts 3 with vertical outer walls. 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 that of the GBS central part 1 (Figures 2 to 4).

[0025] The central portion 1 of the GBS 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 protruding portions 3 of the GBS are separated into compartments by vertical walls 5 perpendicular to their outer walls; 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 foundation 11 is ensured by ballast compartments 7, 8 and 20, which are filled with water.

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

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

[0030] The central part 1 of the GBS has a rectangular prism shape and includes the main support structure, i.e., the vertical longitudinal and transverse walls 5, and horizontal slabs (top slab 2, bottom slab 4, and intermediate support slab 13 below the main tank 12 for storing hydrocarbons and / or the respective processed products). The support structure ensures the necessary spatial rigidity of the GBS frame, including during transportation of the integrated production complex and while it is floating until installation. 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 serve 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 to allow for the drainage of atmospheric precipitation and process spills. 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 technological process, steel with enhanced cryogenic resistance characteristics is used as reinforcement to protect the top slab 2 from spills 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 load from the storage tanks 12 for the liquid hydrocarbons and / or the respective processed products. Longitudinal and transverse walls 14 below this slab 13 transfer the load 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 protruding sections 3 are arranged along the periphery of the GBS central section 1 and form a unitary structure therewith. The long sides of the protruding sections 3 mostly house the ballast compartments 8 (Fig. 5) and the short end sides mostly house the auxiliary and engineering compartments 15. The protruding sections 3 of the GBS serve the following primary purposes: - Achieving the required target GBS buoyancy parameters; - to accommodate a ballast compartment 8 intended primarily to balance the GBS and ensure that it floats evenly without roll and draft adjustments; - to form a natural protective barrier in case of design emergency collision / ship impact, with the protruding portions 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 bearing structure of the main tank 12 and upper foundation; - To accommodate auxiliary processing and ship equipment that ensures LNG carriers can moor and unload liquid hydrocarbons.

[0036] Storage tanks for liquid hydrocarbons and / or their 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 section 1 contains several tanks 12 (Figure 5), which may have different designs depending on the characteristics of the materials to be stored. For the 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 (an 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 tanks 12 and their liquid contents to the aforementioned boundary structures. The GBS slabs and walls thus function as a support structure for the membrane tanks, thereby integrating them into a single structural unit. To prevent any leakage, the bottom and sides of the membrane tank 12 have a secondary barrier, an additional membrane placed inside the insulating layer.

[0037] In the case of an LNG plant, the liquefied gas is stored in two 115,000 cbm tanks 12 each installed in an individual compartment 6 measuring 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 the storage of condensates and other liquid hydrocarbons that do not require low temperatures, GBS concrete compartments 17 may be used, with their boundary structure acting as a protective barrier. Part of compartment 7 can be used for both ballast water and condensates and other liquid hydrocarbons that do not require low temperatures. In the case of an LNG plant, there is compartment 7, measuring 135 x 30 x 30 m with 75,000 cbm, for the storage of stable condensate, and one compartment 17, with a capacity of 5,000 cbm and dimensions of 30 x 8 x 30 m, for the storage of substandard condensate.

[0039] "Wet" storage, which includes 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 1 m thick, is considered a mixing zone that ensures guaranteed separation of water and stored product during the loading operation. Compartment 7 is also slightly pressurized (from atmospheric level) by utilizing a nitrogen blanket at the top of compartment 7 to prevent air from entering compartment 7 and forming flammable and explosive gas mixtures with the hydrocarbon vapors.

[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 for 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, some 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, freestanding tanks are also used in the GBS compartment (in the central section 1 or in the protruding section 3). In the case of an LNG plant, freestanding tanks are used for wastewater, demineralized water, fresh water, wash water, absorbents, butane and propane.

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

[0045] The supports 9 of the upper side 10 on the top slab 2 of the GBS ensure the perception of support reactions from the upper side 10 to the main load-bearing structure of the GBS. Structurally, the supports are reinforced concrete towers with heads for embedded components. At the GBS supports 9 and the upper side 10 connection points, special sealing is used to compensate for 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 upper side 10. A deck 24 supporting the upper side 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 turbines mounted on the upper side 10.

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

[0049] A liquid hydrocarbon unloading pier 21 will be structurally integral with the GBS and upper side. Fenders and unloading platforms with unloading arms and other vessel and processing equipment to allow unloading of liquid hydrocarbons will be installed on the seaward side of the GBS in the overhang 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 GBS is a power generation facility, the main function of the pier will be 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. Generally, a GBS is designed to have three types of compartments: ballast compartments, hydrocarbon storage compartments, and auxiliary and engineering compartments.

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

[0053] An additional ballast section 20 (FIGS. 2 and 4) is located 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 the ballast compartment 8 and the auxiliary and engineering compartment 15. In the case of the GBS LNG plant, the overhang 3 on both sides comprises mostly the ballast compartment 8, while at the short end it comprises mostly the auxiliary and engineering compartment 15.

[0055] The compartments may be separated by transverse partitions, except for the main LNG storage compartment 6. In this case, openings are made inside the ballast compartment to allow ballast water to flow through, and passages for staff and the dissemination 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, on the one hand, stand on the GBS top slab 2 and, on the other hand, stand on the quayside 18. The seabed 25 and the water level 26 in the water body are shown in Figures 2 to 4.

Claims

1. A gravity-grounded structure having a central portion with a rectangular top slab and protruding portions, wherein the central portion is a rectangular prism, the protruding portions extend along both sides of the central portion all around the periphery of the central portion and have outer and inner vertical walls forming ballast compartments on either side of the protruding portions, the protruding portions and the central portion share a rectangular bottom slab, the protruding portions are shorter in height than the central portion, and the central portion has inner vertical longitudinal and lateral walls forming compartments, some of the compartments being ballast compartments, wherein each of the several ballast compartments in the central portion is formed from above by the top slab and from below by the bottom slab.

2. 2. The gravity-based bottom structure of claim 1, characterized in that it has an intermediate horizontal slab with vertical longitudinal and lateral walls that form an additional compartment between the intermediate horizontal slab and the bottom slab.

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