Deep-draft dry tree semi-submersible platform and design method thereof

Abstract

The invention relates to a deep draft dry tree semi-submersible platform which comprises a ship body, a water ballast tank, an upper module and a mooring system, the water ballast tank, the upper module and the mooring system are installed on the ship body, and the ship body comprises a plurality of bypass channels, a plurality of node channels, a plurality of stand columns and a heaving body. A plurality of bypass channels and a plurality of node channels are connected in a staggered mode to form a rectangular-ambulatory-plane frame, a heaving body is arranged on the outer side of the rectangular-ambulatory-plane frame, a stand column is arranged above each node channel, an upper module is arranged above each stand column, water ballast tanks are arranged on the bypass channels and the node channels respectively, and mooring systems are further arranged on the stand columns. The heaving performance of the platform is optimized by additionally arranging the heaving body, optimizing the main scale and draught and the like, the technical requirement for oil extraction of the dry tree is met, the platform application water depth range is wider, the deck area is larger, the variable load is larger, overall installation is easy, economical efficiency is good, and the application range is wide. The method is combined with the advantages of low drilling cost, low operation and maintenance cost and high oil and gas recovery efficiency of a dry Christmas tree.

Description

Technical Field

[0001] The invention relates to the technical field of offshore oil development, in particular to a deep-draft dry-tree semi-submersible platform and a design method thereof. Background Art

[0002] Wet Christmas trees and dry Christmas trees are widely used in deepwater oil and gas development. Compared with wet Christmas trees, dry Christmas trees have the advantages of lower drilling costs, lower operation and maintenance costs, and higher oil and gas recovery rates. Currently, only Spar and TLP, two floating foundation platforms, can use dry Christmas trees. The heave motion cycle of traditional semi-submersible platforms is close to the wave cycle, and the heave motion performance is relatively poor. It is difficult to meet the stroke requirements of the top tensioned riser (TTR). There is currently no actual application case of semi-submersible platforms using dry Christmas trees.

[0003] The installation of Spar modules requires the use of large floating cranes, which has a high overall installation cost. The TLP type is limited in water depth, the platform tendons are expensive, and the installation is complicated. The above two platform types are relatively uneconomical and it is difficult to achieve economic development of isolated oil fields.

[0004] Therefore, a deep draft dry tree semi-submersible platform is urgently needed. Summary of the invention

[0005] On one hand, the present invention provides a deep draft dry tree semi-submersible platform, which has the functions of drilling, oil production, oil and gas processing, oil and gas transmission, etc. On the other hand, the present invention provides a design method for a deep draft dry tree semi-submersible platform.

[0006] A first aspect of the present invention provides a deep-draft dry-tree semi-submersible platform, comprising a hull, a ballast tank, an upper assembly and a mooring system, wherein the ballast tank, the upper assembly and the mooring system are respectively installed on the hull, and the hull comprises a plurality of bypass channels, a plurality of node channels, a plurality of columns and a heave body, a plurality of the bypass channels and a plurality of the node channels are staggeredly connected to form a U-shaped frame, the heave body is arranged on the outer side of the U-shaped frame, and a column is arranged above each of the node channels, the upper assembly is arranged above the column, the ballast tanks are respectively arranged on the bypass channels and the node channels, and the mooring system is also arranged on the column.

[0007] For the deep draft trunk tree semi-submersible platform, preferably, the side length of the cross section of the column forms an angle of 45° with the side length of the adjacent bypass.

[0008] The deep-draft dry-tree semi-submersible platform is preferably provided with transverse channels in both the bypass channel and the node channel, the transverse channels in the bypass channel are connected with the transverse channels in the node channel to form an annular channel, and the ballast water tanks are respectively arranged around the transverse channels in the bypass channel and the transverse channels in the node channel.

[0009] The deep draft dry tree semi-submersible platform is preferably provided with longitudinal channels in the node channel and the column respectively, the longitudinal channel in the node channel is connected with the longitudinal channel in the column, and the ballast water tank is arranged around the longitudinal channel in the node channel and the longitudinal channel in the column.

[0010] The deep-draft dry-tree semi-submersible platform preferably has a mooring system comprising a mooring cable, an anchor chain compartment, an anchor windlass and a fairlead, the mooring cable is provided on the outside of the column, the anchor chain compartment and the anchor windlass are provided on the top of the column, and the fairlead is provided on the bottom outside the column to change the direction of the mooring cable and avoid interference of the mooring cable with the heaving body.

[0011] The deep draft dry-tree semi-submersible platform is preferably provided with a ballast water tank in the heave body and / or the column.

[0012] The deep draft trunk tree semi-submersible platform is preferably configured such that all columns, the node channels and the heave bodies are provided with arc transition sections.

[0013] The deep-draft dry-tree semi-submersible platform is preferably provided with a dry-tree oil production system and a steel catenary at the center of the upper assembly, and a top tensioned riser is also provided on the hull, the dry-tree oil production system is connected to the seabed wellhead via the top tensioned riser, the steel catenary riser is used for the external transmission of oil and gas, and the steel catenary riser is lowered to the seabed along the surface of the column.

[0014] A second aspect of the present invention provides a design method for a deep draft dry tree semi-submersible platform, comprising the following steps: Determine the scale and plan of oilfield development and design the main dimensions of the platform; Designing the volume of the ballast water tank based on the determined main dimensions of the platform and determining whether the ballast water tank is provided on the heave body and the column; The mooring system is designed according to the water depth and environmental conditions of the oil field.

[0015] The deep draft dry-tree semi-submersible platform, preferably, the step of "determining whether the ballast water tank is provided on the heave body and the column" comprises the following specific steps: determining a required ballast water volume based on the main dimensions of the platform, and estimating a required ballast water tank capacity based on the required ballast water volume; The ballast water tanks are arranged on the bypass channel and the node channel. Whether to set the ballast water tanks is determined according to the size of the heaving body. If the capacity of all the ballast water tanks after the heaving body is set with the ballast water tanks meets the required ballast water capacity, the column is not set with the ballast water tank; if the capacity of all the ballast water tanks after the heaving body is set with the ballast water tanks does not meet the required ballast water capacity, the required ballast water tank height is determined in the column according to the required ballast water tank volume.

[0016] The beneficial effects are: The deep-draft dry-tree semi-submersible platform applied for has the advantages of low dry-tree oil tree drilling cost, low operation and maintenance cost, high oil and gas recovery rate, etc., as well as the advantages of a wide range of application water depths of semi-submersible platforms, a large deck area for easy arrangement of production facilities, a large variable load, and simple overall installation.

[0017] The deep-draft dry-tree semi-submersible platform of the present application has excellent motion performance, and the amplitude of heave motion under extreme conditions is only ±2m, which meets the technical requirements of the top tensioned riser.

[0018] The side length of the cross section of the column of the present application forms an angle of 45° with the side length of the adjacent bypass. The upper block is supported by multiple columns, and two supporting nodes are arranged on each column, which reduces the difficulty of the upper block structure design.

[0019] The bypass channel and the node channel of the present application are staggered to form a complete U-shaped frame structure, which is beneficial to improving the overall structural strength of the platform. The present application adopts a heave body type to increase the additional mass and damping of the platform. Compared with the traditional heave plate, the heave body type is more conducive to the design of the connection structure between the heave body and the bypass, and the heave body can provide a larger displacement volume, which is conducive to the overall towing of the platform after integrated installation at the dock, reducing the requirements for the water depth of the dock.

[0020] The column of the present application is located above the node channel connected to the bypass channel, and the two parameters of the length of the bottom U-shaped frame composed of the bypass channel and the node channel and the column span are independent of each other. During the design process, the length of the bottom U-shaped frame can be adjusted without changing the column span to optimize the platform movement performance, and vice versa.

[0021] The design method of the deep-draft dry-tree semi-submersible platform in this application divides the platform design into three relatively independent steps. After the main scale plan is determined, the cabin design and mooring system design can be carried out independently at the same time. The subsequent three-part design can be relatively independently optimized to determine the impact of each parameter on the platform performance. After the optimization of each part is completed, the final verification is carried out together to form a final plan. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the overall structure of this application platform; Figure 2 It is a top view structural diagram of the application platform; Figure 3 It is a schematic diagram of the cabin structure of the platform in this application.

[0023] The symbols in the accompanying drawings are as follows: Hull; 11. Column; 12. Node channel; 13. Bypass channel; 14. Heave body; Upper module; 3. Mooring cable; 4. Windlass; 5. Fairlead; 6. Steel catenary riser; Top tensioned riser; 8. Support node; 91. Ballast water tank; 92. Transverse channel; 93. Longitudinal channel; 94. Chain locker. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0025] In the description of the present invention, it should be noted that the terms "above" and the like indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the system or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0026] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "setting" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] The present invention provides a deep-draft dry-tree semi-submersible platform, comprising a hull, a ballast tank, an upper assembly and a mooring system, wherein the ballast tank, the upper assembly and the mooring system are respectively installed on the hull, and the hull comprises a plurality of bypass channels, a plurality of node channels, a plurality of columns and a heave body, wherein a plurality of the bypass channels and a plurality of the node channels are staggeredly connected to form a U-shaped frame, the heave body is arranged on the outer side of the U-shaped frame, and a column is arranged above each of the node channels, the upper assembly is arranged above the column, the ballast tanks are respectively arranged on the bypass channel and the node channel, and the mooring system is also arranged on the column.

[0028] Example 1 The entire technical process is described in detail below using a deep-draft dry-tree semi-submersible platform as an example.

[0029] Reference Figures 1 to 3 As shown, the present invention provides a deep draft dry tree semi-submersible platform, comprising a hull 1, a ballast water tank 91 and an upper block 2 on the hull 1 of a mooring system, wherein the ballast water tank 91, the upper block 2 and the mooring system are respectively installed on the hull 1; The hull 1 includes four columns 11, four node channels 12, four bypass channels 13 and a heave body 14. The four node channels 12 and the four bypass channels 13 are staggered to form a U-shaped frame; the four columns 11 are respectively located above the four node channels 12, and the heave body 14 is located on the outside of the U-shaped frame formed by the staggered connection of the four node channels 12 and the four bypass channels 13; the upper module 2 is supported by the four columns 11, and can realize the functions of drilling, oil production, oil and gas processing, and oil and gas export. A trunk tree oil production system (not shown in the figure) is arranged at the center of the upper module 2, and a top tensioning riser 7 is also arranged on the hull 1. The trunk tree oil production system is connected to a submarine wellhead (not shown in the figure) through the top tensioning riser 7, and oil and gas are exported through a steel catenary riser 6. The steel catenary riser 6 is arranged along any one of the columns 11, and the steel catenary riser 6 is lowered to the seabed along the surface of the column 11 close to the center of the hull 1.

[0030] Furthermore, four columns 11 are located above four node channels 12, and the two parameters of the length of the bottom U-shaped frame formed by the node channel 12 and the bypass channel 13 and the span between the columns 11 are independent of each other. The size of the U-shaped frame can be modified while maintaining the span of the columns 11 unchanged, or the position of the columns 11 can be moved while maintaining the size of the bottom U-shaped frame to adjust the span of the columns 11. Therefore, the two parameters can be analyzed and studied independently during the design process to minimize the coupling effect of the two on the platform performance. The size of the bottom U-shaped frame can be adjusted to adjust the platform motion performance, and the span between the columns 11 can be adjusted to adjust the platform stability. It is possible to achieve optimal platform motion performance and stability at the same time, reducing design redundancy.

[0031] Furthermore, the cross-sectional side lengths of the four columns 11 are at an angle of 45° to the side lengths of the adjacent bypass channels 13. The upper assembly 2 is connected to each column 11 via two support nodes 8. In conventional platform column arrangements, there is usually only one support point between each column and the upper assembly. In the present platform, two support points 8 can be arranged between each column and the upper assembly. The number of support points for the upper assembly is greater and relatively dispersed, thereby reducing the difficulty in designing the overall structural strength of the upper assembly 2.

[0032] Reference Figure 3 As shown, transverse channels 93 for pipeline layout and maintenance inspection are provided inside the four node channels 12 and the four bypass channels 13. The transverse channels 93 inside the node channels 12 and the transverse channels 93 inside the bypass channels 13 are interconnected to form an annular channel.

[0033] The interiors of the four node channels 12 and the interiors of the four columns 11 are provided with longitudinal channels 94 for pipeline layout and maintenance inspection. The longitudinal channels 94 inside the columns 11 and the node channels 12 are interconnected to form four longitudinal channels 94; the transverse channels 93 inside the node channels 12 are interconnected with the longitudinal channels 94 in a cross shape.

[0034] The transverse channel 93 and the longitudinal channel 94 in the entire hull 1 are integrally connected, which simplifies the pipeline layout and subsequent operation and maintenance, and improves work efficiency.

[0035] Continue to refer to Figure 3 As shown, a ballast water tank 91 is arranged around the transverse channel 93 inside the bypass channel 13, a ballast water tank 91 is arranged around the transverse channel 93 and the longitudinal channel 94 inside the node channel 12, a ballast water tank 91 is arranged around the longitudinal channel 94 in the lower half of the column 11, and an anchor chain compartment 92 and other equipment compartments (not shown in the figure) are arranged in the upper half, and the ballast water tanks 91 are adjacent to the transverse channel 93 or the longitudinal channel 94 to facilitate the arrangement of the ballast discharge system.

[0036] Continue to refer to Figure 1 and Figure 3 As shown, in order to ensure the accurate positioning of the new deep-draft dry-tree semi-submersible platform, a multi-point mooring system is used to position the platform. Four mooring cables 3 are provided on the outside of the four columns 11, a chain compartment 92 is provided at the uppermost end of the column 11, a windlass 4 is provided on the top of the column 11, and a fairlead 5 is provided on the bottom outside the column 11 to change the direction of the mooring cables 3 and avoid interference between the mooring cables 3 and the heave body 14.

[0037] Continue to refer to Figure 3 As shown, the interior of the heave body 14 is separated by a ballast water tank 91, and the ballast water tank 91 is filled with fixed ballast material, which can be seawater or iron ore, to reduce the overall center of gravity height of the platform and comprehensively improve the platform's movement performance and stability.

[0038] Among them, the heave body 14 should maintain a certain height to facilitate the structural design of the connecting part between the heave body 14 and the node channel 12 and the bypass channel 13; at the same time, the heave body 14 provides a larger displacement volume, which is conducive to the overall towing of the platform after integrated installation at the dock, reducing the towing draft of the platform and reducing the requirements for the dock water depth and tugboat.

[0039] Furthermore, all the columns 11, the node channels 12, and the heave bodies 14 are provided with arc transitions, and the connection between the columns 11 and the node channels 12 is provided with arc transitions to reduce stress concentration.

[0040] Example 2 A design method for a deep-draft dry-tree semi-submersible platform is proposed. The three steps of main scale design, cabin design and mooring system design are independent of each other. The platform adopts the design concept of separate column and node channel design and the design concept that the side length of the column cross section and the side length of the adjacent bypass channel are at a 45° angle. The two parameters that should be strongly related in the main scale design, the column span and the bottom return frame size, are independent of each other, so that the optimization work of each parameter and each step can be carried out independently. This method can be used to guide the design of semi-submersible platforms with deep draft and small vertical swing, optimize the design ideas of semi-submersible platforms, and reduce the difficulty of platform optimization.

[0041] A design method for a deep draft semi-submersible platform includes: Step 1: Determine the scale and plan of oil field development and design the main dimensions of the platform.

[0042] The step 1 specifically includes the following steps: The first step is to determine the scale and plan of oil field development, and determine the main deck area and upper module weight.

[0043] The second step is to determine the height of the main deck from the water surface based on the oil field environmental conditions.

[0044] The third step is to select parameters such as platform column span, column size, bypass channel size, and platform draft.

[0045] The fourth step is to estimate the displacement and center of buoyancy of the platform based on the determined platform size.

[0046] The fifth step is to estimate the empty ship weight and center of gravity height of the platform based on the determined platform dimensions.

[0047] Step 6: Determine the ballast water weight and center of gravity height based on the estimated platform displacement, platform empty ship weight, upper module weight, riser weight, mooring system weight and other weight information.

[0048] The seventh step is to determine the weight and center of gravity of the platform at the designed draft position, and evaluate whether the initial stability height margin of the semi-submersible platform meets the requirements. In this embodiment, it is assumed that the initial stability height of the semi-submersible platform is not less than 5m. If the initial stability height is ≥5m, proceed to the eighth step. If the initial stability height is <5m, return to the third step to re-evaluate the optimization parameters.

[0049] The eighth step is to evaluate whether the natural periods of heave, roll and pitch of the semi-submersible platform meet the requirements. In this embodiment, it is assumed that the natural period of heave is not less than 23s, and the natural period of roll and pitch is not less than 40s. If the natural periods of the three degrees of freedom meet the above requirements, the main scale design is completed. If not, return to the third step to optimize the parameters for re-evaluation.

[0050] Step 2: Design the volume of the ballast water tank based on the determined main dimensions of the platform and determine whether the ballast water tank is provided on the heave body and the column.

[0051] The step 2 specifically includes the following steps: S1: Determine the required ballast water volume based on the ballast water weight determined in step 6 of the main scale design process. In this embodiment, the ballast water tank loading capacity does not exceed 98%, and the required ballast water tank capacity is estimated based on this.

[0052] S2: Determine the scale parameters and positions of the transverse and longitudinal channels used for pipeline layout and maintenance inspection in the bypass channel, node channel and column of the platform. The transverse and longitudinal channels are arranged as much as possible at the center of the cross section of the bypass channel, the node channel and the column to ensure that the surrounding cabins are as similar in size as possible and are adjacent to the channel.

[0053] S3: Ballast water tanks are all arranged in the bypass channel and the transverse and longitudinal channels in the node channel for pipeline layout and maintenance inspection. Whether to arrange ballast water tanks is determined according to the size of the heave body. If ballast water tanks are arranged in the heave body, the ballast water tanks arranged in the heave body are connected with the ballast water tanks in the bypass channel. If the capacity of the ballast water tanks in the bypass channel, the heave body and the node channel meets the required capacity of the ballast water tanks, step S5 is directly performed; if the required capacity of the ballast water tanks is not met, step S4 is performed; S4: The required height of the ballast water tank is determined in the column according to the required ballast water tank volume.

[0054] That is, the difference is obtained by subtracting the capacity of the bypass channel, the node channel and the ballast water tank arranged in the vertical swing body from the required ballast water tank capacity, and the height of the ballast water tank arranged by the column is set using this difference.

[0055] S5: Other functional compartments are arranged on the upper part of the column, including but not limited to: fresh water tank, SLOP tank, diesel tank and anchor chain tank.

[0056] S6: Carry out the stability check of the platform in case of cabin damage. If the design requirements are met, the cabin design is completed. If the requirements are not met, return to step S3 to optimize the cabin size and recheck.

[0057] Step 3: Design the mooring system according to the water depth and environmental conditions of the oil field.

[0058] The step three specifically includes the following steps: 1) Preliminarily determine the mooring radius, number of mooring cables, components and lengths of each part of the mooring cables, and the location of the mooring cables based on the water depth and environmental conditions of the oil field.

[0059] 2) Evaluate whether the semi-submersible platform movement and mooring cable force meet the requirements. If they meet the requirements, complete the mooring system design. If they do not meet the requirements, modify the mooring related parameters and re-evaluate. In this embodiment, the platform needs to use a dry oil tree, which has a high requirement for the platform stroke and needs to meet the requirement that the platform stroke does not exceed 30ft.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A deep draft dry tree semi-submersible platform, comprising a hull, a ballast tank, an upper block and a mooring system, wherein the ballast tank, the upper block and the mooring system are respectively installed on the hull, characterized in that: The hull includes a plurality of bypass channels, a plurality of node channels, a plurality of columns and a heave body. The plurality of bypass channels and the plurality of node channels are staggeredly connected to form a U-shaped frame. The heave body is provided on the outer side of the U-shaped frame. In addition, a column is provided above each of the node channels, and the upper block is provided above the column. The ballast water tanks are respectively arranged on the bypass channels and the node channels, and the mooring system is also provided on the columns.

2. The deep draft dry tree semi-submersible platform according to claim 1, characterized in that: The side length of the cross section of the column forms an angle of 45° with the side length of the adjacent bypass.

3. The deep draft dry tree semi-submersible platform according to claim 2, characterized in that: The bypass channel and the node channel are both provided with transverse channels, the transverse channel in the bypass channel is connected with the transverse channel in the node channel to form an annular channel, and the ballast water tank is respectively arranged around the transverse channel in the bypass channel and the transverse channel in the node channel.

4. The deep draft dry tree semi-submersible platform according to claim 3 is characterized in that: The node channel and the column are respectively provided with longitudinal channels, the longitudinal channel in the node channel is connected with the longitudinal channel in the column, and the ballast water tank is arranged around the longitudinal channel in the node channel and the longitudinal channel in the column.

5. The deep draft dry tree semi-submersible platform according to claim 4 is characterized in that: The mooring system includes a mooring cable, a chain locker, an anchor windlass and a fairlead. The mooring cable is provided on the outside of the column, the chain locker and the anchor windlass are provided on the top of the column, and the fairlead is provided on the bottom of the outside of the column to change the direction of the mooring cable and avoid interference of the mooring cable with the heaving body.

6. The deep draft dry tree semi-submersible platform according to claim 5, characterized in that: The ballast water tank is also provided in the heave body and / or the column.

7. The deep draft dry tree semi-submersible platform according to claim 5, characterized in that: All the columns, the node channels and the heave bodies are provided with arc transition sections.

8. The deep draft dry tree semi-submersible platform according to any one of claims 1 to 7, characterized in that: A trunk tree oil production system and a steel catenary are arranged at the center of the upper assembly block. A top tensioned riser is also arranged on the hull. The trunk tree oil production system is connected to the seabed wellhead via the top tensioned riser. The steel catenary riser is used for the external transmission of oil and gas. The steel catenary riser is lowered to the seabed along the surface of the column.

9. A design method for a deep draft dry-tree semi-submersible platform as claimed in any one of claims 1 to 8, characterized in that: The steps include: Determine the scale and plan of oilfield development and design the main dimensions of the platform; Designing the volume of the ballast water tank based on the determined main dimensions of the platform and determining whether the ballast water tank is provided on the heave body and the column; The mooring system is designed according to the water depth and environmental conditions of the oil field.

10. The deep draft dry tree semi-submersible platform according to claim 9, characterized in that: The step of "determining whether the ballast water tank is provided on the heave body and the column" comprises the following specific steps: determining a required ballast water volume based on the main dimensions of the platform, and estimating a required ballast water tank capacity based on the required ballast water volume; The ballast water tanks are arranged on the bypass channel and the node channel. Whether to set the ballast water tanks is determined according to the size of the heaving body. If the capacity of all the ballast water tanks after the heaving body is set with the ballast water tanks meets the required ballast water capacity, the column is not set with the ballast water tank; if the capacity of all the ballast water tanks after the heaving body is set with the ballast water tanks does not meet the required ballast water capacity, the required ballast water tank height is determined in the column according to the required ballast water tank volume.

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