Polyester Cable Mooring Tensioning Method for Semi-Submersible Production Platform

Abstract

The invention discloses a polyester cable mooring tensioning method for a semi-submersible production platform, which relates to the technical field of offshore oil engineering. The polyester cable mooring tensioning method for a semi-submersible production platform is provided with four groups of platform windlasses at the four corners of the semi-submersible production platform, and a chain stopper is arranged on each windlass. Each group of platform windlasses is provided with at least 4. The polyester cable mooring is connected to the semi-submersible platform through the windlass. The tensioning method includes the following steps: S1: The operation ship and the semi-submersible production platform complete the transfer of the polyester cable mooring. The platform windlass continues to recover the anchor leg. After recovering a certain length, the chain stopper locks. When recovering the anchor leg, the recovered length is determined by the 10th - 12th chain links of the platform chain passing through the chain stopper of the platform windlass. The invention can realize the safe and efficient tensioning of the polyester cable by using the semi-submersible production platform and the windlass system, reduce the residual deformation of the polyester cable during service, and ensure the safety of the semi-submersible production platform.

Description

Technical Field

[0001] The present invention relates to the technical field of offshore oil engineering, and particularly to a polyester cable mooring tensioning method for a semi-submersible production platform. Background Art

[0002] With the gradual development of offshore oil and gas resources towards deep water, the application of floating production platforms and mooring systems has gradually become mature. Due to characteristics such as high strength, light weight, and good fatigue resistance, polyester cables have broad application prospects in the mooring systems of floating production platforms.

[0003] However, according to the properties of polyester cables such as stretching, creep, and stiffness, after the mooring anchor leg is connected back to the platform, tensioning is required. The tensioning force is usually 40% of the minimum breaking force of the polyester cable, and generally the tensioning force reaches more than 300 tons. It is impossible to use an engineering ship to perform tensioning according to the method of traditional steel cable mooring installation. Therefore, a polyester cable mooring tensioning technology is very necessary for the mooring system of a deep-water semi-submersible production system. Summary of the Invention

[0004] The purpose of the present invention is to provide a polyester cable mooring tensioning method for a semi-submersible production platform to solve the problems raised in the above background art.

[0005] To achieve the above purpose, the present invention provides the following technical solution: A polyester cable mooring tensioning method for a semi-submersible production platform, including the semi-submersible production platform, with four groups of platform capstans provided at the four corners, and chain stoppers are provided on each capstan. Each group of platform capstans has at least 4. The polyester cable mooring is connected to the semi-submersible platform through the capstan, and the polyester cable mooring is numbered from #1 to #16 in a clockwise direction. The polyester cable mooring includes connected platform chain, anchor leg, anchor pile, and anchor pile chain. The platform chain is provided with chain links, and its tensioning method includes the following steps:

[0006] S1: The workboat and the semi-submersible production platform complete the transfer of the polyester cable mooring. The platform capstan continues to retrieve the anchor leg. After retrieving a certain length, the chain stopper locks.

[0007] S2: The platform capstan retrieves the platform chain of the first group of #1 polyester cable mooring to a predetermined length, and repeats the above operation to retrieve the platform chains of the first group of #2, #3, and #4 polyester cable moorings to a predetermined length.

[0008] S3: Release the platform chains of the three anchor legs of the first group of #2, #3, and #4 to the state before tensioning.

[0009] S4: Retrieve all the platform chains of the four anchor legs of the diagonal third group of #9, #10, #11, and #12 to a predetermined length to make the tensioning load of the #1 polyester cable mooring reach the design tension.

[0010] S5: Relax the four anchor legs numbered #9, #10, #11, and #12 in the third group to the specified length, and the tensioning of the #1 anchor leg is completed;

[0011] S6: Conduct the tensioning operation on the remaining three anchor legs in the first group;

[0012] S7: Conduct the tensioning operation on the four diagonal anchor legs numbered #9, #10, #11, and #12 in the third group;

[0013] S8: Conduct the tensioning operation on a total of eight anchor legs in the second group and the fourth group.

[0014] Furthermore, when recovering the anchor legs in step S1, the recovery length is determined by the 10th - 12th link of the platform chain passing through the chain stopper of the platform anchor winch.

[0015] Furthermore, in step S5, the polyester cable mooring tensioning load is generally set to 40% of the minimum breaking force of the polyester cable.

[0016] Furthermore, in step S5, when the reading of the chain stopper of the tensioned polyester cable anchor leg drops by more than 5%, a set of diagonal anchor legs needs to be further recovered to make the force of the tensioned polyester cable anchor leg reach the predetermined value again.

[0017] Furthermore, in step S4, after reaching the design tension, the polyester cable starts to be gradually stretched and maintained for 3 hours until the length of the polyester cable increases by about 2%.

[0018] Furthermore, after step S8, the tensioning of the 16 anchor legs is completed, and then the entire mooring system is finely adjusted until the loads of all chain stoppers reach the design values.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] This method for tensioning the polyester cable mooring of a semi - submersible production platform can achieve the safe and efficient tensioning of the polyester cable by using a semi - submersible production platform and an anchor winch system, reduce the residual deformation of the polyester cable during service, and ensure the safety of the semi - submersible production platform. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the overall layout diagram of the mooring system of the deep - water semi - submersible production platform of the present invention;

[0022] Figure 2 It is the underwater structure diagram of the mooring system of the present invention;

[0023] Figure 3 It is the overall layout schematic diagram of the anchor winch system of the semi - submersible production platform of the present invention;

[0024] Figure 4 It is the structural schematic diagram of the anchor winch system of the present invention;

[0025] Figure 5 This is a schematic diagram of the operation of recovering a set of four polyester cables of the semi-submersible platform of the present invention;

[0026] Figure 6 This is a schematic diagram of the operation of releasing a set of three polyester cables of the semi-submersible platform of the present invention;

[0027] Figure 7 This is a schematic diagram of the operation of recovering a set of four diagonal polyester cables of the semi-submersible platform of the present invention;

[0028] Figure 8 This is a schematic diagram of the operation of releasing a set of four diagonal polyester cables of the semi-submersible platform of the present invention.

[0029] In the figure: No. 1 - No. 16 are all polyester cable moorings. Detailed implementation manners

[0030] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0031] It should be noted that in the description of the present invention, the orientation or positional relationships indicated by the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0032] In addition, it should be understood that for the convenience of description, the sizes of the various components shown in the accompanying drawings are not drawn according to the actual proportional relationships. For example, the thickness or width of some layers may be exaggerated relative to other layers.

[0033] It should be noted that similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined or described in one drawing, it will not be necessary to further discuss and describe it specifically in the description of the subsequent drawings.

[0034] When fixing a semi-submersible production platform, polyester mooring cables are used, and the polyester mooring cable tensioning method for the semi-submersible production platform provided by the present invention is adopted to tension the used polyester mooring cables, so as to achieve good fixation of the semi-submersible production platform. During the tensioning process, the operation of retracting / extending the mooring anchor legs is realized by the operator operating the platform windlass. The following will be described in conjunction with the accompanying drawings to specifically elaborate on the entire polyester mooring cable tensioning method.

[0035] As Figures 1-8 shown, the present invention provides a technical solution: a polyester mooring cable tensioning method for a semi-submersible production platform, including a semi-submersible production platform, with four groups of platform windlasses provided at the four corners. Hawse pipes are provided on each windlass, and at least 4 are provided for each group of platform windlasses. Polyester mooring cables are provided on each windlass, and the polyester mooring cables are numbered from #1 to #16 in a clockwise direction. In the figure, they are respectively denoted as ML1 - ML16 corresponding to the platform windlasses. Only ML1, ML2, ML3, ML4, and ML9, ML10, ML11, ML12 on its diagonal are marked in the figure, and the remaining ones are simplified and not marked. The polyester mooring cable includes a platform chain, an anchor leg, an anchor pile, and an anchor pile chain connected to each other. The platform chain is provided with chain links. The purpose of the present invention is to provide a deep-water polyester mooring cable tensioning method, which utilizes the characteristics of the semi-submersible production platform and the mooring system to study a set of safe and efficient polyester cable pre-tensioning schemes. This scheme first relaxes some mooring cables in a certain mooring system, causing a change in the stiffness of the mooring system and resulting in the offset of the semi-submersible production platform, thereby stretching the polyester mooring cables that are not relaxed in this group. In this way, all the polyester mooring cables are tensioned by taking turns. The tensioning method includes the following steps:

[0036] As Figures 3-4 shown, S1: The workboat completes the transfer of the polyester mooring cable with the semi-submersible production platform. The platform windlass continues to retract the anchor leg. After retracting a certain length, the hawse pipe locks. When retracting the anchor leg, the retraction length is determined by the 10th - 12th chain links of the platform chain passing through the hawse pipe of the platform windlass. It should be noted that the number of chain links set needs to be adjusted according to the actual use situation;

[0037] As Figure 5 shown, S2: The platform windlass retracts the platform chain of the first group of #1 polyester mooring cable to a predetermined length, and repeats the above operation to retract the platform chains of the first group of #2, #3, and #4 polyester mooring cables to a predetermined length;

[0038] As Figure 6 shown, S3: Release the platform chains of the three anchor legs of the first group of #2, #3, and #4 to the state before tensioning;

[0039] As Figure 7As shown, S4: Recover all four anchor leg platform chains of the third diagonal group, namely #9, #10, #11, and #12, to a predetermined length, so that the mooring tension load of the #1 polyester cable reaches the design tension. After reaching the design tension, the polyester cable begins to be gradually stretched and maintained for 3 hours until the length of the polyester cable increases by about 2%;

[0040] As Figure 8 shown, S5: Relax the four anchor legs of the third group, namely #9, #10, #11, and #12, to the specified length. The tensioning of the #1 anchor leg is completed. The mooring tension load of the polyester cable is generally set to 40% of the minimum breaking force of the polyester cable. When the reading of the chain stopper of the tensioned polyester cable anchor leg drops by more than 5%, a set of diagonal anchor legs needs to be further recovered to make the force on the tensioned polyester cable anchor leg reach the predetermined value again;

[0041] S6: Repeat the above steps to carry out the tensioning operation of the remaining three anchor legs of the first group;

[0042] S7: Repeat the above steps to carry out the tensioning operation of the four anchor legs of the third diagonal group, namely #9, #10, #11, and #12;

[0043] S8: Repeat the above steps to carry out the tensioning operation of a total of eight anchor legs of the second group and the fourth group. After step S8, the tensioning of the 16 anchor legs is completed. Subsequently, fine-tune the entire mooring system until the load of all chain stoppers reaches the design value.

[0044] After the polyester cable is tensioned, conduct an installation survey on all 16 anchor legs through the ROV, and record the coordinates, water depth, status, and the number of twists of the anchor legs at their key points (including all connectors such as quick connectors and polyester cable shackles). The twist of the subsea chain does not exceed 2 turns, the twist of the platform chain does not exceed 1 turn, and the twist of a single polyester cable does not exceed 9.5 turns.

[0045] It should be noted that in step S1, all 16 anchor legs need to be transferred and recovered to the platform before starting the tensioning operation of the polyester cable. The receiving / discharging operation of the mooring anchor legs is realized by the operator operating the platform anchor winch. In step S4, when the reading of the chain stopper of the tensioned polyester cable anchor leg drops by more than 5%, a set of diagonal anchor legs needs to be further recovered to make the force on the tensioned polyester cable anchor leg reach the predetermined value again.

[0046] In summary, the platform mooring winch retrieves the platform chain moored by the first set of four polyester cables to a predetermined length; the platform mooring winch releases the platform chain moored by the first set of three polyester cables to the state before tensioning; the platform mooring winch retrieves the platform chain moored by the third diagonal set of four polyester cables to a predetermined length, so that the tension load of the first polyester cable moored by the first set reaches the design tension, and the polyester cable begins to gradually stretch and is maintained for 3 hours; the platform chain moored by the third set of four polyester cables is relaxed to a specified length to complete the tensioning of the first polyester cable moored by the first set; the above steps are repeated for the tensioning operations of the remaining polyester cables; the entire mooring system is finely adjusted until the load of all chain stoppers reaches the design value; after tensioning, an investigation is carried out on all 16 polyester cable anchor legs through the ROV. Thus, the tensioning of the polyester cables can be safely and efficiently carried out by using the semi-submersible production platform and the mooring winch system, reducing the residual deformation of the polyester cables during service and ensuring the safety of the semi-submersible production platform.

[0047] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made in these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A polyester cable mooring tensioning method for a semi-submersible production platform, characterized in that: The semi-submersible production platform is provided with four groups of platform mooring winches at its four corners. Each mooring winch is equipped with a chain stopper. Each group of platform mooring winches has at least 4. The polyester cable mooring is connected to the semi-submersible platform through the mooring winch, and the polyester cable mooring is numbered from #1 to #16 in a clockwise direction. The polyester cable mooring includes a connected platform chain, anchor leg, anchor pile, and anchor pile chain. The platform chain is provided with chain links. Its tensioning method includes the following steps: S1: The workboat completes the transfer of the polyester cable mooring with the semi-submersible production platform. The platform mooring winch continues to recover the anchor leg. After recovering a certain length, the chain stopper locks. S2: The platform mooring winch recovers the platform chain of the first group of #1 polyester cable mooring to a predetermined length. Repeat the above operation to recover the platform chains of the first group of #2, #3, and #4 polyester cable moorings to a predetermined length. S3: Release the anchor leg platform chains connected by the first group of #2, #3, and #4 polyester cable moorings to the state before tensioning. S4: Recover all the anchor leg platform chains connected by the third group of #9, #10, #11, and #12 polyester cable moorings at the diagonal to a predetermined length, so that the tensioning load of the first group of #1 polyester cable mooring reaches the design tension. S5: Relax the anchor legs connected by the third group of #9, #10, #11, and #12 polyester cable moorings to the specified length, and the tensioning of the anchor legs connected by the first group of #1 polyester cable mooring is completed. S6: Carry out the tensioning operation of the remaining three anchor legs connected by the first group of polyester cable moorings. S7: Carry out the tensioning operation of the anchor legs connected by the third group of #9, #10, #11, and #12 polyester cable moorings at the diagonal. S8: Carry out the tensioning operation of the anchor legs connected by a total of eight polyester cable moorings in the second and fourth groups.

2. The polyester cable mooring tensioning method for the semi-submersible production platform according to claim 1, wherein: In the S1 step, when recovering the anchor leg, the recovery length is determined by the 10th - 12th chain links of the platform chain passing through the chain stopper of the platform mooring winch.

3. The polyester cable mooring tensioning method for the semi-submersible production platform according to claim 1, wherein: In the S5 step, the tensioning load of the ester cable mooring is set to 40% of the minimum breaking force of the polyester cable.

4. The polyester cable mooring tensioning method for the semi-submersible production platform according to claim 1, characterized in that: In the S5 step, when the reading of the chain stopper of the tensioned polyester cable anchor leg drops by more than 5%, it is necessary to further recover a group of anchor legs at the diagonal to make the force of the tensioned polyester cable anchor leg reach the predetermined value again.

5. The polyester cable mooring tensioning method for the semi-submersible production platform according to claim 1, characterized in that: In the S4 step, after reaching the design tension, the polyester cable starts to be gradually stretched and maintained for 3 hours until the length of the polyester cable increases by about 2%.

6. The polyester cable mooring tensioning method for the semi-submersible production platform according to claim 1, characterized in that: After the S8 step, the tensioning of the 16 anchor legs is completed, and then the entire mooring system is finely adjusted until the load of all chain stoppers reaches the design value.

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