Offshore mobile platform shallow pitching pile shoe local scour protection method

Abstract

The invention discloses a local scour protection method for shallow pitching of a pile shoe of an offshore mobile platform. The method comprises the following steps that S1, the size of a scour protection suction barrel is determined according to the size of the pile shoe and a seabed stratum structure; s2, the suction barrel penetrates into the seabed; and S3, the offshore mobile platform pile shoe is inserted into the suction barrel penetrating into the seabed. On the premise that an existing offshore mobile platform is not transformed, the risk hidden dangers of scouring, undercutting and transverse sliding of shallow pile shoes of the offshore mobile platform in a well site area where piles are repeatedly inserted and pulled are fundamentally solved. The installation depth of the suction barrel is larger than the maximum wave-caused seabed liquefaction depth and the scouring limit balance depth, long-term stability of the suction barrel is ensured, and reliable puncture and sliding protection is provided for the pile shoe; on the other hand, the height of the suction cylinder is larger than the sum of the thickness of the liquefiable seabed and the height of the pile shoe, the height of the cylinder wall exposed out of the seabed is not smaller than the height of the pile shoe, direct impact of water flow on the seabed around the pile shoe can be directly blocked, and local scouring and undercutting are thoroughly avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ocean engineering, in particular to a method for local scour protection of shallowly inserted pile shoes of offshore mobile platforms. BACKGROUND

[0002] Mobile platforms are mainly used for drilling and workover operations in offshore oil and gas production. When working on site, pile legs with pile shoes are deeply inserted into the seabed to ensure stability and sufficient bearing capacity under the attack of sea waves. When the seabed soil is relatively dense, the pile legs of the mobile platform may be inserted too shallowly, and the pile shoes may be at risk of scouring and lateral sliding due to not being fully inserted into the mud, which may result in unknown platform stability and pose a great safety hazard.

[0003] In the related art of scour protection, more technical research and development are carried out for offshore wind power pile foundations, which usually include laying stones, oyster shells, bionic waterweeds or old tires around the wind power pile foundation to reinforce the seabed and reduce scouring. These technologies are suitable for long-term fixed foundations such as wind power pile foundations. Since the laid scour protection materials permanently change the structure of the seabed, they will be obstacles that cannot be avoided for subsequent pile insertion for offshore mobile platform pile foundations that often need to carry out repeated pile insertion and extraction operations in the same well site area. Therefore, the above-mentioned technical methods cannot be applied. In view of the problem that offshore mobile platform pile shoes are difficult to insert into hard seabed, a related technical invention proposes to blast the hard stratum before the mobile platform is in place to damage the stratum structure and reduce the bearing capacity, so as to achieve deep insertion of the pile shoe into the mud. However, this method needs to carry out underwater blasting operations, which is technically difficult and costly, especially for granular soil layers that may have rapid backfilling and unsatisfactory actual results. Another technical path is to modify the offshore mobile platform pile shoe, such as adding a high-pressure water jet erosion device to damage the hard layer of the seabed during pile insertion to achieve deep pile insertion. Alternatively, an active protection cylinder is added to the pile leg, which wraps the pile leg to avoid direct impact of the water flow on the pile foundation and reduce the scouring and loss of silt around the pile foundation. Since this type of technology involves modifying the existing offshore mobile platform pile foundation, it needs to be evaluated by platform safety and stability professionals, and the technical difficulty of implementation is also great, and long-term maintenance of the equipment also faces great difficulties. SUMMARY

[0004] The present application aims to provide a convenient, economical, practical and environmentally friendly method for local scour protection of shallowly inserted pile shoes of offshore mobile platforms.

[0005] To achieve the above-mentioned purpose, the present application provides a method for local scour protection of shallowly inserted pile shoes of offshore mobile platforms, comprising the following steps: S1: determining the size of the scour protection suction cylinder according to the size of the pile shoe and the structure of the seabed stratum; S2: drive the suction cylinder into the seabed; S3: insert the offshore mobile platform spudcan into the suction cylinder which has been driven into the seabed.

[0006] Preferably, the diameter of the suction cylinder in step S1 is greater than the diameter of the spudcan, and the height of the suction cylinder is greater than the sum of the thickness of the liquefiable seabed and the height of the spudcan.

[0007] Preferably, the specific method of step S2 is as follows: S21: hoist the suction cylinder to the seabed area where the offshore mobile platform is to be installed, and use underwater precise positioning technology to ensure that the suction cylinder foundation matches the installation position; S22: after the suction cylinder is in place, initially drive it into the seabed under its own weight, and the seawater and air in the suction cylinder are naturally discharged through the top valve; S23: use vacuum negative pressure technology to continue slowly driving the suction cylinder into the seabed to the designed depth.

[0008] Preferably, the installation depth of the suction cylinder in step S23 is greater than the maximum depth of wave-induced seabed liquefaction and the equilibrium depth of scour limit, and the suction cylinder wall is exposed above the seabed to protect the shallow spudcan from local scour.

[0009] Preferably, during the negative pressure driving process in step S23, the internal negative pressure of the suction cylinder, the driving depth of the suction cylinder foundation, and the inclination of the cylinder body are monitored in real time, and the suction control parameters of the vacuum system are dynamically adjusted according to the monitoring data to avoid soil seepage failure or cylinder deformation buckling.

[0010] Preferably, the negative pressure driving process in step S23 adopts a process of staged vacuum pumping and step-by-step sinking, and after each stage of vacuum pumping, the pressure is kept stable, and after the suction cylinder foundation stops sinking, the next stage of negative pressure is lifted.

[0011] Preferably, the specific method of step S23 is as follows: S231: start the vacuum pumping system at a low negative pressure in the initial stage, slowly lift the internal negative pressure value of the suction cylinder to the first set value, and the first negative pressure value is 0.02~0.03MPa lower than the external seawater pressure corresponding to the seabed surface of the installation area; S232: keep the current negative pressure value stable for 3~5min, and during this period, the sinking data of the suction cylinder foundation is collected in real time by the underwater displacement monitoring device; S233: if the sinking amount of the suction cylinder foundation is ≤2mm within 10min, it is determined that the current stage stops sinking; S234: then perform the next stage of vacuum pumping, and the negative pressure lifting amplitude of each stage is controlled to be 0.01~0.02MPa; S235: repeat the pressure stable keeping and sinking stop determining process of steps S232~S233 until the suction cylinder foundation sinks to the designed depth.

[0012] Preferably, the top cover of the suction cylinder in step S1 is detachable, and after step S2 is completed, the top cover of the suction cylinder is removed for recycling.

[0013] Compared with the prior art, the application has the following advantages: (1) The application fundamentally solves the risk of repeated insertion and extraction of the pile well field area of the offshore mobile platform, without modifying the existing offshore mobile platform. The installation depth of the suction cylinder is greater than the maximum depth of wave-induced seabed liquefaction and the scour limit equilibrium depth, ensuring its long-term stability and providing reliable puncture and sliding protection for the pile shoe. On the other hand, the height of the suction cylinder is greater than the sum of the height of the pile shoe and the thickness of the liquefiable seabed, and the height of the cylinder wall exposed above the seabed is not less than the height of the pile shoe, which can directly block the direct impact of water flow on the seabed around the pile shoe, completely avoiding local scouring and erosion. At the same time, the presence of the suction cylinder enhances the vertical bearing capacity of the seabed, further improving the support stability of the shallow pile shoe, and fundamentally ensuring the long-term stability and safety of the offshore mobile platform drilling and workover operations.

[0014] (2) The application perfectly adapts to the repeated insertion and extraction of the pile operation of the mobile platform, solving the compatibility defects of the prior art. The suction cylinder in the application adopts a movable top cover design, which can be recycled after installation, leaving a precise insertion port for the pile shoe to dock, without affecting the pile insertion operation. The suction cylinder as a whole can be recycled and reused, and can be completely removed after the operation is completed, without leaving any obstacles on the seabed. It completely adapts to the operation requirements of repeated insertion and extraction of the pile in the same well field area, filling the gap in the mobile platform's exclusive anti-scour technology. (3) Compared with the high cost and high difficulty of underwater blasting technology, and the high evaluation and maintenance cost of modifying the platform pile shoe, the application reduces the operation cost and the impact on the ecological environment, with significant economic and environmental benefits. Specifically, by learning from the mature installation experience of the suction cylinder foundation of offshore wind power, there is no need to develop new construction technology, the construction process is standardized, the technical research and construction difficulty are greatly reduced, and the construction cost is saved. The top cover and overall structure of the suction cylinder can be recycled and reused, avoiding the waste of disposable protective materials and significantly reducing the cost of consumables. In addition, the installation is achieved by self-weight penetration and negative pressure during the construction process, which minimizes the disturbance to the seabed soil and does not damage the marine ecological environment, and there is no need for subsequent seabed repair operations, which takes into account the environmental benefits and long-term operating cost control.

[0015] (4) The present invention is convenient and reliable to construct, requires no modification to the existing platform, is highly practical, and does not require any structural modification to the existing offshore mobile platform, thus avoiding the complex process and technical risks of platform safety and stability assessment. It can be directly adapted to various existing drilling and well repair mobile platforms. The construction process relies on mature technologies such as engineering vessel hoisting and underwater precise positioning, and the operation process is clear. Moreover, by monitoring the negative pressure, penetration depth and cylinder inclination in real time, the suction parameters can be dynamically adjusted, effectively avoiding installation failures such as soil seepage damage and cylinder deformation and buckling, resulting in high construction reliability. At the same time, the mobile platform can achieve precise docking of the pile shoe and suction cylinder with positioning accuracy, further improving the convenience of operation and facilitating on-site promotion and application. Attached Figure Description

[0016] Figure 1 This is a diagram showing the external shape of the suction cylinder foundation in the method for protecting the shallow-pile boots of offshore mobile platforms according to the present invention. Figure 2 This is a schematic diagram of the suction cylinder installation in the method for protecting the shallow-inserted pile shoe of a marine mobile platform according to the present invention; Figure 3 This is a schematic diagram of the suction cylinder installation position in the method for local scour protection of shallow-inserted pile shoes for offshore mobile platforms according to the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] This invention provides a method for protecting shallow-pile shoes of offshore mobile platforms from localized scour, comprising the following steps: S1: Determine the dimensions of the scour protection suction cylinder based on the pile shoe size and seabed strata structure. In this example, the suction cylinder is a steel cylinder with hooks and a movable top cover, with a suction valve installed at the top cover. The diameter of the suction cylinder should be larger than the diameter of the pile shoe to ensure that the pile shoe can be inserted into the suction cylinder. Figure 1 The height of the suction cylinder should be greater than the sum of the thickness of the liquefiable seabed and the height of the pile shoe to ensure the stability of the suction cylinder foundation in the event of wave-induced seabed liquefaction and to ensure that the cylinder wall has sufficient height to protrude above the seabed after the pile shoe is inserted into the suction cylinder to protect against local scouring of shallowly inserted pile shoes. Figure 2 In addition, the top cover of the suction cylinder is detachable, and can be recycled and reused after the suction cylinder foundation is installed in the predetermined position. It can also provide an insertion port for the pile shoe.

[0019] S2: Insert the suction cylinder into the seabed. For offshore mobile platforms engaged in drilling and well workover activities, the location of the staking is relatively fixed, generally within a certain range near the fixed offshore oil and gas production platform. Based on the wellhead layout of the fixed platform, the installation location of the scour protection suction cylinder can be determined from the angle that is convenient and quick for the offshore mobile platform to be positioned. Figure 3 After determining the foundation installation location for the scour protection suction cylinder, the installation of the scour protection suction cylinder will be carried out by drawing on the mature installation experience of offshore wind power suction cylinders. Specific methods: S21: The suction cylinder is hoisted to the seabed area to be installed by the engineering vessel, and underwater precision positioning technology is used to ensure that the foundation of the suction cylinder matches the intended installation location; S22: After the suction cylinder is in place, it initially penetrates the seabed under its own weight, and the seawater and air inside the suction cylinder are naturally discharged through the top valve; S23: Utilize vacuum negative pressure technology to slowly lower the suction cylinder to the designed depth. This depth should be greater than the maximum depth of wave-induced seabed liquefaction and the scour limit equilibrium depth to ensure the long-term stability of the suction cylinder. This provides puncture and slip protection for the shallow-insertion pile shoes of the offshore mobile platform. Simultaneously, sufficient height should be exposed above the seabed around the suction cylinder walls to protect against localized scour of the shallow-insertion pile shoes; this height should not be less than the height of the mobile platform pile shoes. Throughout the suction cylinder installation process, the negative pressure, suction cylinder penetration depth, and cylinder inclination should be monitored. The suction control parameters of the vacuum system should be dynamically adjusted based on the monitoring data to prevent installation failures such as soil seepage damage or cylinder deformation and buckling. Specific methods: S231: In the initial stage, the vacuum system is started with low negative pressure to slowly increase the negative pressure value inside the suction cylinder to the first-level set value. The first-level negative pressure value is 0.02~0.03MPa lower than the external seawater pressure corresponding to the seabed surface of the installation area. S232: Maintain the current negative pressure value for 3~5 minutes, during which the sinking data of the suction cylinder foundation is collected in real time through the underwater displacement monitoring device; S233: If the sinking of the suction cylinder foundation is ≤2mm within 10 minutes, the sinking of the current stage is judged to have stopped; S234: Then proceed to the next stage of vacuuming, with the negative pressure increase controlled at 0.01~0.02MPa for each stage; S235: Repeat steps S232~S233 to maintain pressure stability and determine the sinking stop until the suction cylinder foundation sinks to the design depth.

[0020] After the suction cylinder foundation is installed, the cylinder cover will be recycled and reused, while also providing an insertion port for the subsequent mobile platform pile shoes.

[0021] S3: Insert the mobile platform pile shoe into the suction cylinder that has penetrated the seabed. Since the mobile platform can achieve a positioning accuracy of <1m when the piles are driven into place, the mobile platform pile shoe can be accurately inserted into the foundation of the suction cylinder based on the coordinates of the suction cylinder installed in step 23. The part of the suction cylinder foundation that is higher than the seabed can provide protection against local scouring of the shallowly driven pile shoe, while the presence of the suction cylinder also enhances the vertical bearing capacity of the seabed, providing better support for the safety of the mobile platform pile shoe.

[0022] The anti-scour principle of the shallow-inserted pile shoe local scour protection method of the present invention for offshore mobile platforms is as follows: the suction cylinder can be slowly and precisely installed into the seabed by applying negative pressure. When the cylinder wall is higher than the seabed by a certain height, it can provide scour protection for the pile shoe of the offshore mobile platform inserted therein. At the same time, it improves the vertical bearing capacity of the seabed, reduces the risk of pile shoe puncture and slippage, and provides better support for the stable operation of the mobile platform.

[0023] The above technical methods can completely eliminate the risks of erosion and lateral slippage of shallow-inserted pile shoes on offshore mobile platforms, ensuring the long-term stability and safety of drilling and well repair operations. Furthermore, the suction cylinder foundation can be recycled using hooks, saving resources and protecting the marine ecological environment.

[0024] This invention fundamentally solves the risks of erosion and lateral slippage of shallow-inserted pile shoes on offshore mobile platforms in areas with repeated pile insertion and removal without modifying existing offshore mobile platforms. This invention causes minimal disturbance to the seabed, and the anti-erosion suction cylinder is recyclable, resulting in significant environmental and economic benefits. This invention draws on mature technology and experience in offshore suction cylinder foundations, making construction convenient, less difficult, and with good practicality and durability.

[0025] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for localized scour protection of shallow-pile shoes on offshore mobile platforms, characterized in that, Includes the following steps: S1: Determine the size of the scour protection suction cylinder based on the size of the pile shoe and the seabed strata structure; S2: Insert the suction tube into the seabed; S3: Insert the offshore mobile platform pile shoe into the suction cylinder that has penetrated the seabed.

2. The method for local scour protection of shallow-pile shoes for offshore mobile platforms according to claim 1, characterized in that, In step S1, the diameter of the suction cylinder is greater than the diameter of the pile shoe, and the height of the suction cylinder is greater than the sum of the thickness of the liquefiable seabed and the height of the pile shoe.

3. The method for local scour protection of shallow-pile shoes for offshore mobile platforms according to claim 2, characterized in that, The specific method for step S2: S21: Hoist the suction cylinder to the seabed area where it is to be installed, and use underwater precision positioning technology to ensure that the foundation of the suction cylinder matches the intended installation location; S22: After the suction cylinder is in place, it initially penetrates the seabed under its own weight, and the seawater and air inside the suction cylinder are naturally discharged through the top valve; S23: Use vacuum negative pressure technology to continue to slowly press the suction cylinder down to the designed depth.

4. The method for local scour protection of shallow-pile shoes for offshore mobile platforms according to claim 3, characterized in that, In step S23, the installation depth of the suction cylinder is greater than the maximum depth of wave-induced seabed liquefaction and the scour limit equilibrium depth, and the cylinder wall is exposed around the seabed to protect the shallow-sunken piles from local scour.

5. The method for local scour protection of shallow-pile shoes for offshore mobile platforms according to claim 3, characterized in that, During the negative pressure installation process in step S23, the negative pressure inside the suction cylinder, the penetration depth of the suction cylinder, and the inclination of the cylinder are monitored in real time. The suction control parameters of the vacuum system are dynamically adjusted according to the monitoring data to avoid soil seepage damage or cylinder deformation and buckling.

6. The method for local scour protection of shallow-pile shoes for offshore mobile platforms according to claim 3, characterized in that, In step S23, the negative pressure installation adopts a process of staged vacuuming and step-by-step sinking. After each stage of vacuuming, the pressure is kept stable, and the next stage of negative pressure lifting is carried out only after the suction cylinder foundation stops sinking.

7. The method for local scour protection of shallow-pile shoes for offshore mobile platforms according to claim 6, characterized in that, The specific method for step S23: S231: In the initial stage, the vacuum system is started with low negative pressure to slowly increase the negative pressure value inside the suction cylinder to the first-level set value. The first-level negative pressure value is 0.02~0.03MPa lower than the external seawater pressure corresponding to the seabed surface of the installation area. S232: Maintain the current negative pressure value for 3~5 minutes, during which the sinking data of the suction cylinder foundation is collected in real time through the underwater displacement monitoring device; S233: If the sinking of the suction cylinder foundation is ≤2mm within 10 minutes, the sinking of the current stage is judged to have stopped; S234: Then proceed to the next stage of vacuuming, with the negative pressure increase controlled at 0.01~0.02MPa for each stage; S235: Repeat steps S232~S233 to maintain pressure stability and determine the sinking stop until the suction cylinder foundation sinks to the design depth.

8. The method for local scour protection of shallow-pile shoes for offshore mobile platforms according to claim 3, characterized in that, The top cover of the suction cylinder in step S1 is detachable. After completing step S2, the top cover of the suction cylinder is removed and recycled.

Images