Lightweight three-column semi-submersible offshore platform

Abstract

The present application relates to a kind of light three-column semi-submersible offshore platform, it includes three groups of heave tank, regular triangle distribution;Three columns, respectively vertically arranged in the upper of three groups described heave tank;Rectangular pontoon, connect between adjacent described heave tank.By the above structural configuration, the present application uses high load ratio three-column semi-submersible structure as foundation, reduces the steel consumption, improves economic effect, simultaneously, the connecting point of inclined brace and column is moved down, optimizes the stress state of column, further improves the overall structural strength of platform.Through setting only in the heave pipe opening triangular web in the region surrounded by heave tank and rectangular pontoon, the connection mode of the platform is optimized, can effectively block underwater vortex, increase heave motion damping, to improve the horizontal and vertical motion performance of platform under the action of wave flow, can well adapt to the characteristics of short development cycle, diversified functional requirements of deep water marginal oil field.

Description

Technical Field

[0001] This invention relates to a semi-submersible offshore platform, particularly a lightweight three-column semi-submersible offshore platform, which uses a high load-bearing ratio three-column semi-submersible structure as its foundation, reducing steel consumption and improving economic efficiency. At the same time, by moving the connection point between the diagonal brace and the column downward, the stress state of the column is optimized, further enhancing the overall structural strength of the platform. Background Technology

[0002] Offshore oil and gas exploration has become a core pillar of the global oil and gas industry, with mobile offshore platforms, especially semi-submersible platforms, playing a crucial role in deepwater oil and gas field development. After decades of development, traditional semi-submersible platforms generally adopt a four- or six-pillar structure, with a box-shaped deck, and their function has expanded from single-function drilling to multi-functional equipment integrating drilling, production, and storage. However, when facing numerous deepwater marginal oil fields in regions like the South China Sea with small reserves, short development cycles, and sensitive economic benefits, traditional multi-pillar semi-submersible platforms have revealed problems such as structural redundancy leading to huge steel consumption and insufficient economic efficiency. Furthermore, the large number of pillars makes node connections complex, making them prone to fatigue damage under alternating marine loads; the deck layout is limited by the pillar distribution, and large-span structures are prone to insufficient pressure-bearing capacity.

[0003] Against this backdrop, the three-post semi-submersible platform has re-emerged due to its inherent triangular stability and high load-to-weight ratio, and is considered more suitable for the development of small and medium-sized platforms. However, existing three-post platform technologies are mostly concentrated in the offshore wind power sector, with relatively small superstructure loads and a primary focus on stability in wind and waves, failing to fully realize its potential in heavy-duty, multi-functional scenarios such as oil and gas processing and drilling. A few three-post platforms applied in the oil and gas sector still follow traditional structural designs, without systematic optimization of diagonal bracing, crossbeams, and superstructure connections, resulting in significant room for improvement in their load-to-weight ratio, space utilization, and multi-functional expansion capabilities. Summary of the Invention

[0004] To address the aforementioned deficiencies in existing technologies, this invention provides a lightweight three-column semi-submersible offshore platform. It employs a high load-bearing ratio three-column semi-submersible structure as its foundation, reducing steel consumption and improving economic efficiency. Furthermore, by lowering the connection point between the diagonal brace and the column, the stress state of the column is optimized, further enhancing the overall structural strength of the platform.

[0005] To achieve the above objectives, the present invention provides a lightweight three-pillar semi-submersible offshore platform, comprising: Three sets of helical chambers are arranged in an equilateral triangle; Three pillars are respectively vertically installed above the three sets of heave chambers; Rectangular pontoons are connected between adjacent helical cabins; A triangular web is provided within the area enclosed by the heave chamber and the rectangular pontoon; The upper crossbeam is connected to the top of the adjacent column; Diagonal bracing connects the column and the upper crossbeam; The upper module, located on top of the upper beam and the column, provides living and working space.

[0006] Traditional multi-column semi-submersible platforms suffer from structural redundancy, leading to excessive steel consumption and economic inefficiency. To address this, this invention employs three columns as the supporting foundation, reducing steel consumption and resolving the economic issue.

[0007] The heave chamber and the column both have circular cross-sections, and the column is coaxially arranged with the heave chamber.

[0008] The upper module is connected to the top of the upper beam and the column via a detachable support structure.

[0009] The upper module adopts a modular design and includes at least three independent and detachable functional modules.

[0010] The column is a hollow structure, with a watertight compartment inside.

[0011] The upper crossbeam is a hollow structure and is configured to be used as a utility tunnel.

[0012] It also includes a positioning system, which includes a mooring device installed on each of the posts and a dynamic positioning thruster installed below the waterline of the posts.

[0013] The mooring device includes three sets of cables, each set of cables including three mooring cables, one end of which is anchored to a post and the other end is anchored to the seabed.

[0014] Each of the columns is equipped with three propellers, which are distributed at 120° equidistant angles around the side of the column.

[0015] The triangular web is 1.5-2 meters thick and has an opening only at the penetration point of the helical chamber.

[0016] Through the above structural design, this invention adopts a high load-bearing ratio three-column semi-submersible structure as its foundation, reducing steel consumption and improving economic efficiency. Simultaneously, the connection point between the diagonal braces and the columns is moved downwards, optimizing the stress state of the columns and further enhancing the overall structural strength of the platform. By setting a triangular web with openings only at the heave tube within the area enclosed by the heave chamber and the rectangular pontoon, the connection method of the platform is optimized, effectively blocking underwater eddies and increasing heave motion damping, thereby improving the platform's horizontal and vertical motion performance under wave and current action. By designing the support between the upper module and the main structure as a non-permanent connection with detachable and shock-absorbing functions, flexible replacement of the upper module is achieved, avoiding construction waste and structural damage caused by cutting and welding. It also isolates the upper module from the impact of severe sea conditions on acceleration, facilitating standardized design of the upper module. Furthermore, by setting the columns and upper beams as hollow structures and using them as functional compartments or pipe racks, the platform's space utilization and load-bearing ratio are improved. Based on the above improvements, the lightweight three-pillar semi-submersible offshore platform of the present invention maintains its economic advantages while possessing stronger structural reliability, motion stability, and multi-functional expansion capabilities, and can well adapt to the characteristics of short development cycles and diversified functional requirements of deep-water marginal oil fields. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of Embodiment 1 of the lightweight three-pillar semi-submersible offshore platform of the present invention; Figure 2 This is an elevation view of Embodiment 1 of the lightweight three-pillar semi-submersible offshore platform of the present invention; Figure 3 This is a schematic diagram of the overall structure of Embodiment 2 of the lightweight three-pillar semi-submersible offshore platform of the present invention; Figure 4 This is a mooring system design drawing of Embodiment 2 of the lightweight three-pillar semi-submersible offshore platform of the present invention; Figure 5 This is an elevation view of Embodiment 2 of the lightweight three-pillar semi-submersible offshore platform of the present invention; Figure 6 This is a schematic diagram of the overall structure of Embodiment 3 of the lightweight three-pillar semi-submersible offshore platform of the present invention; Figure 7 This is an elevation view of Embodiment 3 of the lightweight three-pillar semi-submersible offshore platform of the present invention; Figure 8 This is a top view of Embodiment 3 of the lightweight three-pillar semi-submersible offshore platform of the present invention. Detailed Implementation

[0018] The directions or similar terms used throughout this invention, such as "front," "back," "left," "right," "top," "bottom," "inner," "outer," and "side," are mainly for reference to the directions in the accompanying drawings. These directions or similar terms are only used to assist in explaining and understanding the various embodiments of this invention and are not intended to limit this invention.

[0019] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. However, the embodiments described are only used to illustrate the technical features of the present invention and are not intended to limit the scope of protection of the present invention.

[0020] Please see Figures 1 to 8 As shown, the lightweight three-column semi-submersible offshore platform of the present invention has three cylindrical heave chambers 1 at its bottom, which are arranged in an equilateral triangle. The lower parts of adjacent heave chambers 1 are welded together by rectangular pontoons 3, forming a stable triangular floating foundation. Above each heave chamber 1, a cylindrical column 2 is coaxially arranged, meaning the cross-section of the column 2 is concentric with the cross-section of the heave chamber 1, and the three columns 2 are also arranged in an equilateral triangle. The tops of the three columns 2 are connected together by an upper crossbeam 5. Furthermore, from the lower part of each column 2, approximately 1 / 4 to 1 / 3 of its height, a diagonal brace 4 extends, which supports the upper crossbeam 5, forming a stable triangular support structure together with the columns 2 and the upper crossbeam 5. Both the diagonal brace 4 and the upper crossbeam 5 use thickened cylindrical cross-sections, thus replacing the traditional complex truss structure, simplifying node connections, and reducing stress concentration. The connection point between the diagonal brace 4 and the column 2 is set as low as possible, according to the principles of mechanics. It can be seen that when the angle θ between the diagonal brace and the horizontal plane increases, the horizontal component force Fcosθ exerted by the diagonal brace on the column will decrease accordingly, while the vertical component force Fsinθ will increase. This is beneficial to convert more of the external load into the axial pressure that the column is good at, thus optimizing the mechanical performance of the platform.

[0021] Within the internal area enclosed by the aforementioned triangular floating foundation, specifically the space between the heave chamber 1 and the rectangular pontoon 3, a triangular web 10 is provided. This triangular web 10 is a solid plate located below the waterline, with a thickness of 1.5 to 2 meters. It opens only at the point where the heave chamber 1 penetrates, thus avoiding obstruction of the heave chamber 1's structure. This triangular web 10 has multiple functions: firstly, it can block underwater lateral currents, reducing the lateral impact of waves on the support column, making the current force more uniform, and reducing the platform's lateral drift; secondly, it can cut off the formation path of underwater eddies, reducing eddies generated by the interaction between the ocean current and the support column; thirdly, it can increase the damping of the platform's heave motion, that is, improve vertical stability by increasing the resistance to the platform's vertical movement in the water. It should be noted that in some special embodiments, such as when the platform needs to have a drilling opening, a small opening can also be made in the central area of ​​the triangular web 10.

[0022] Please see Figure 2 , Figure 5 and Figure 7 The three columns 2 mentioned above all adopt a hollow structure, and their interiors are divided into multiple independent watertight compartments 12. These watertight compartments 12 can be flexibly utilized according to the different functional requirements of the platform: when used as an oil and gas processing platform, they can be used as storage tanks for crude oil or natural gas; when used as a drilling platform, they can be used as storage tanks for fuel oil and spare equipment, as well as spare buoyancy tanks with adjustable displacement; when used as a natural gas liquefaction processing platform, deacidification, dehydration, mercury removal and other processing equipment can be directly arranged in the watertight compartments of different columns. The upper crossbeam 5 is designed as a thickened hollow structure, thus serving as a pipe gallery, further increasing the usable space and improving the platform's load-bearing capacity.

[0023] The main structure of the platform is connected to the upper module via a support structure 13. Unlike traditional permanent welding fixation, the support structure 13 in this invention is designed to be detachable and shock-absorbing. Specifically, at least one connection between the support structure 13, the upper beam 5, and the upper module is a non-permanent connection. For example, a mortise and tenon structure with a small interference fit and screws can be used for detachable fixation; a sliding rail with angle iron limiter can be used to achieve limited relative sliding to buffer impact; or non-linear damping viscoelastic connecting components such as rubber can be used to absorb vibration energy. Through the above design, on the one hand, when the platform function needs to be changed, the upper module can be easily disassembled and replaced in whole or in part without cutting and re-welding the support structure, improving work efficiency and avoiding structural damage caused by welding; on the other hand, the shock-absorbing design can effectively mitigate the instantaneous impact force transmitted to the upper module when the platform body sways in wind and waves, improving the acceleration environment of the upper module, thereby facilitating the standardized design of the upper module and making its design conditions less restricted by specific sea conditions.

[0024] Please see Figure 1 , Figure 3 , Figure 6 The upper module of the platform adopts a modular design, that is, it is divided into multiple independent functional modules according to functional requirements. These modules may include, but are not limited to: lower process deck 6, upper process deck 7, common room module 8, living quarters module 9, drilling module 22, drilling process equipment module 23, FLNG storage tank 27, etc. Each module can be independently installed and disassembled through the aforementioned detachable support structure 13. Depending on the platform's intended use, the overall shape of the superstructure can vary accordingly. For example, when used as an oil and gas processing platform, a double-trapezoidal deck can be used to distribute most of the weight within the equilateral triangle formed by the three columns 2, preventing an excessively high center of gravity. When used as a drilling platform, a herringbone deck can be used, with the drilling module 22, living quarters module 9, and common room module 8 positioned directly above the three columns 2, utilizing the high load-bearing capacity of the columns 2 to directly support the heavy modules. When used as a natural gas liquefaction processing platform, a large circular deck can be used, concentrating the processing equipment within the triangular area, while lightweight facilities such as solar panels 26 are arranged on the outer edge, and wave deflectors 25 are installed to protect the deck equipment. This modular design allows the same main structure to be easily transformed into different functional types of offshore platforms by replacing and reassembling the superstructure modules.

[0025] Please see Figure 3 and Figure 4 In terms of positioning, the platform of this invention employs a dual positioning method combining a mooring system and a dynamic positioning system. The mooring system uses a 3×3 arrangement, with each group of mooring cables having an angle of 120° between them and each individual cable having an angle of 5° between them. The mooring cables have a three-section structure: anchor chains at the top and bottom, and polyester cable in the middle section, equipped with online tensioners to ensure tension strength and durability. The dynamic positioning system uses distributed dynamic positioning thrusters 24. The specific installation positions of the dynamic positioning thrusters 24 are below the waterline of the pillars 2. Three dynamic positioning thrusters 24 are installed on the outer ring of each pillar 2. The three thrusters on the same pillar 2 are distributed at 120° equidistant angles around the side of the pillar, thus providing thrust in any direction as auxiliary dynamic positioning, further improving positioning accuracy and redundancy in harsh sea conditions.

[0026] The technical solution of the present invention will be further illustrated by the following three specific embodiments.

[0027] Example 1 (Oil and Gas Processing Platform) Please see Figure 1 , Figure 2 and Figure 4Each rectangular pontoon 3 measures 10m wide and 4m high. The heave chamber 1 is 4m high and 24m in diameter, and the column 2 is 24m high and 18m in diameter, with a designed full-load water depth of 12 to 14m. The diagonal bracing 4 extends from approximately one-third of the column's height at the bottom, connecting to the middle section of the upper crossbeam 5. The bottom triangular web 10 is 2m thick and opens only at the heave chamber. The watertight compartment 12 inside the column 2 stores oil and gas and serves as a buoyancy reserve. The upper module is divided into three independent modules: a double-trapezoidal process deck, a common room module 8, and a living quarters module 9. The double-trapezoidal process deck includes a lower trapezoidal process deck 6 and an upper trapezoidal process deck 7. The living quarters 9 can accommodate 80 to 120 people. The trapezoidal deck design allows most of the equipment weight to fall within the equilateral triangle formed by the three columns, which helps lower the center of gravity and improve maneuverability. The supporting structure 13 is permanently connected to the upper crossbeam 5 at one end and non-permanently connected at the other. The non-permanent connection end uses a small interference mortise and tenon structure with screws for fixation, and a non-linear damping viscoelastic connection component (such as rubber) is installed to achieve vibration reduction. The viscoelastic material can be easily replaced by controlling the temperature. Multi-point mooring is used for positioning.

[0028] Example 2 (Drilling Platform) Please see Figures 3 to 5 The platform consists of a 20m diameter, 4m high helical chamber 1, a rectangular pontoon 3 8m wide and 4m high, and a 24m high, 14m diameter support column 2, designed for a water depth of 10-12m. The bottom triangular web 10 is 2m thick with a small opening in the center to allow drilling equipment to pass through. The diagonal brace 4 starts approximately one-third of the column height. The upper modules include a common room module 8, a living quarters module 9, a drilling module 22, and a drilling equipment module 23. The living quarters module 9 has a helicopter landing pad on top. Since the three major weight modules—common room module 8, living quarters module 9, and drilling equipment module 23—are located near the three supports, the connection points of the diagonal brace 4 are closer to the ends of the upper crossbeam 5 to provide maximum structural strength. The support column 2 employs a three-section variable cross-section design: the lower section has an increased cross-sectional area to reduce stress per unit area; the section near the waterline has a reduced cross-sectional area to extend the platform's natural swaying period and avoid the main wave energy peak; and the upper section has a further increased cross-sectional area to better support the heavy upper modules. The watertight compartment 12 inside column 2 serves as a storage area for fuel, spare equipment, and spare buoyancy. The upper module adopts a herringbone design, arranging the drilling module 22, drilling process equipment module 23, living quarters module 9, and common room module 8 respectively, with the three major weight modules located directly at the top of the three columns. The support structure 13 is equipped with a sliding rail and angle iron limiter between it and the main structure to achieve shock absorption, and a small interference mortise and tenon structure with screws allows for disassembly between it and the upper module. Three dynamic positioning thrusters 24 are installed below the waterline of each of the three columns 2 as an auxiliary dynamic positioning system, used in conjunction with multi-point mooring to achieve precise positioning in harsh sea conditions.

[0029] Example 3 (Natural Gas Liquefaction Processing Platform) Please see Figure 4 , Figures 6 to 8 The heave chamber 1 has a diameter of 30m and a height of 6m. The lower rectangular pontoon 3 is 22m wide and 4m high. The column 2 is 32m high, with a diameter of 30m at the top and bottom and a diameter of 25m in the middle. The designed full-load water depth is 20 to 22m. The diagonal brace 4 starts from about 1 / 4 of the column height and connects to the middle section of the upper crossbeam 5. The bottom triangular web 10 is 2m thick and opens only at the heave chamber. The cross-section of the watertight compartment 12 inside the column 2 is enlarged to house the natural gas deacidification, dehydration, and mercury removal equipment. The upper crossbeam 5 is thickened and hollow, serving as a pipe gallery connecting the treatment facilities inside the three columns 2 to form a complete natural gas pretreatment process. The upper module adopts a large-area circular design. The FLNG processing area 701, the utility area 702, and the living area 703 are concentrated in the triangular area enclosed by the first column 201, the second column 202, and the third column 203. Solar panels 26 are arranged on the outer edge, and wave-breaking plates 25 are installed at the deck edge. The superstructure includes a double-trapezoidal process deck, a common room module 8, a living quarters module 9, and an FLNG storage tank 27. The double-trapezoidal process deck comprises a lower trapezoidal process deck 6 and an upper trapezoidal process deck 7. Deacidification, dehydration, and mercury removal processes are carried out in a sealed environment within the columns, while heavy hydrocarbon fractionation and liquefaction processes are conducted on the deck to prevent temperature variations from affecting the column structure's strength. The FLNG storage tank 27, 20m in diameter and 40m high, is located on the deck, with an inner wall made of low-temperature resistant nickel-steel alloy and an outer layer of multi-layer insulation material. The electricity generated by the solar panels 26 is stored in batteries within the common system and can be used to power the dynamic positioning system for daily needs and in harsh sea conditions. The positioning method employs a combination of multi-point mooring and dynamic positioning to provide sufficient positioning redundancy.

Claims

1. A lightweight three-pillar semi-submersible offshore platform, characterized in that, Include: Three sets of helical chambers (1) are arranged in an equilateral triangle; Three columns (2) are respectively vertically installed above the three sets of heave chambers (1); A rectangular pontoon (3) is connected between adjacent helical cabins (1); A triangular web (10) is provided in the area enclosed by the heave chamber (1) and the rectangular pontoon (3); The upper crossbeam (5) is connected to the top of the adjacent column (2); Diagonal brace (4) is connected between the column (2) and the upper crossbeam (5); The upper module is located on top of the upper beam (5) and the column (2) to provide living and working space.

2. The lightweight three-pillar semi-submersible offshore platform according to claim 1, characterized in that, The cross-sections of the heave chamber (1) and the column (2) are both circular, and the column (2) is coaxially arranged with the heave chamber (1).

3. The lightweight three-pillar semi-submersible offshore platform according to claim 1, characterized in that, The upper module is connected to the top of the upper beam (5) and the column (2) via a detachable support structure (13).

4. The lightweight three-pillar semi-submersible offshore platform according to claim 1, characterized in that, The upper module adopts a modular design, including at least three independent and detachable functional modules.

5. The lightweight three-pillar semi-submersible offshore platform according to claim 1, characterized in that, The column (2) is a hollow structure, and a watertight compartment (12) is formed inside it.

6. The lightweight three-pillar semi-submersible offshore platform according to claim 1, characterized in that, The upper crossbeam (5) is a hollow structure and is configured to be used as a pipe gallery.

7. The lightweight three-pillar semi-submersible offshore platform according to claim 1, characterized in that, It also includes a positioning system, which includes a mooring device on each of the posts (2) and a dynamic positioning thruster (24) located below the waterline of the posts (2).

8. The lightweight three-pillar semi-submersible offshore platform according to claim 7, characterized in that, The mooring device includes three sets of cables, each set of cables including three mooring cables, one end of which is anchored to a post (2) and the other end is anchored to the seabed.

9. The lightweight three-pillar semi-submersible offshore platform according to claim 7, characterized in that, Each of the columns (2) is provided with three of the thrusters (24), and the three thrusters (24) are distributed at a 120° equidistant angle around the side of the column (2).

10. The lightweight three-pillar semi-submersible offshore platform according to claim 1, characterized in that, The thickness of the triangular web (10) is 1.5-2 meters, and it is only opened at the through position of the helical chamber (1).

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