A method for dismantling a dual-vessel floating offshore platform

Abstract

The present invention discloses a dual-ship floating offshore platform dismantling method, which belongs to the technical field of offshore platform dismantling, and is characterized by comprising two crane ships equipped with motion compensation devices, two connecting arms that are in direct contact with the upper assembly, and a transport ship. After the upper assembly and the jacket of the offshore platform are cut, the two crane ships unload to reduce the draft, and lift the upper assembly as a whole through the connecting arms connected to the motion compensation device, and move the upper assembly away from the jacket and transport it to the top of the transport ship. During this process, the motion compensation device controls the actuation of the actuator by detecting the posture of the crane ship and the connecting arm to keep the contact point with the connecting arm stable, thereby ensuring the stability of the upper assembly during the lifting and transportation process. When using the present invention to dismantle the offshore platform, the length of the connecting arm and the connection position with the motion compensation device can be selected according to the operation object, and the applicability is strong. At the same time, the use of large floating cranes and the rental of expensive special floating ships are avoided, thereby significantly reducing costs.

Description

Technical Field

[0001] The invention belongs to the technical field of marine engineering, in particular to a method for dismantling a double-vessel floating marine platform. Background Art

[0002] Offshore platforms are mainly dismantled through lifting and floating methods. The lifting method requires the rental of large, expensive crane vessels, while the floating method, especially the double-vessel floating method, is susceptible to the impact of wave environment loads and requires waiting for a sufficient window period or operating through specialized ships, which is expensive.

[0003] Therefore, designing a dual-vessel float-over method for dismantling an offshore platform that can ensure the stability of the topsides during dismantling, expand the operational window, and eliminate the need for large floating cranes or specialized float-over vessels, thereby significantly reducing dismantling costs, remains an urgent technical challenge in this field. Summary of the Invention

[0004] In view of the problems and shortcomings of the prior art, the present invention provides a dual-vessel floating offshore platform dismantling method, which avoids the need for large floating cranes or special vessels with high manufacturing and leasing costs during the dismantling process, thereby reducing the cost of dismantling the offshore platform.

[0005] The objective of the present invention is achieved through the following technical solutions: A method for dismantling a dual-ship floating offshore platform, wherein the offshore platform includes a jacket and an upper assembly, and is characterized in that a transport ship and two crane ships are used in the process of dismantling the upper assembly, and the two crane ships are equipped with a collaborative dynamic positioning system, a displacement control system and two connecting arms, and a laser ranging sensor is installed on the connecting arm, and the laser ranging sensor is used to detect the distance between the upper assembly and the jacket. The two crane ships are respectively equipped with a ballast water tank, a side thruster, two large cranes and two motion compensation devices, and the motion compensation device includes a posture sensor, an actuator and a ball joint connecting the crane ship and the connecting arm. The two large cranes are used to lift the two connecting arms, and the two ends of the connecting arm are used to be connected to the two motion compensation devices on the two crane ships respectively. The method for dismantling the upper assembly of the offshore platform includes the following construction steps:

[0006] Step 1: The following work must be completed before dismantling the upper assembly:

[0007] Step 1.1: The offshore platform has completed the wellhead abandonment work, and a suitable climate window is selected to prepare for the upper module removal operation of the offshore platform;

[0008] Step 1.2: Select a matching connecting arm according to the size of the offshore platform to be dismantled and determine the installation position of the motion compensation device on the deck of the crane vessel;

[0009] Step 1.3: The two crane vessels are respectively arranged on either side of the offshore platform. The drafts of the crane vessels are adjusted simultaneously to ensure that the upper support points of the motion compensation devices are at the same level, and that the connecting arms remain horizontal and their upper surfaces are lower than the bottom surface of the offshore platform. The collaborative dynamic positioning system calculates the operating position, and the collaborative dynamic positioning system ensures the coordinated accuracy of the two crane vessels during the operation.

[0010] Step 1.4: Two large cranes are installed on the side of a crane ship. The two large cranes are used to lift the two connecting arms. One end of each connecting arm is connected to the corresponding motion compensation device on the same crane ship via a ball joint installed on the top of the motion compensation device. The connecting arm is vertically aligned with the crane ship and the centerline of the two crane ships.

[0011] Step 1.5: The two crane vessels move toward the offshore platform through the displacement control system, and the rotation speed of the thrusters is adjusted through the coordinated positioning system to ensure that the two crane vessels have the same speed during the approach process;

[0012] Step 1.6: When the two crane vessels arrive at the designated location, the other ends of the two connecting arms are respectively connected to the corresponding two motion compensation devices on the other crane vessel, and the large crane releases the hooks connected to the connecting arms. The load of the connecting arms is completely borne by the motion compensation devices installed on the decks of the two crane vessels;

[0013] Step 1.7: The crane vessel reduces its draft by discharging loads through the ballast water tank, so that the top surfaces of the two connecting arms contact the bottom surface of the upper assembly and generate a certain pre-pressure;

[0014] Step 1.8: Cutting and separating the upper assembly block from the jacket;

[0015] Step 2: After completing the preparatory work before demolition, start the overall demolition of the upper assembly, including the following steps:

[0016] Step 2.1: Synchronously start the two crane vessels to unload and drain water, controlling the unloading speed to be the same, so that the load of the upper module is gradually transferred from the jacket to the two connecting arms;

[0017] Step 2.2: The two connecting arms are connected to the two crane vessels via motion compensation devices. The crane vessels and connecting arms are equipped with attitude sensors. The attitude sensors measure the changes in the positions of the crane vessels and connecting arms during the removal of the upper modules of the offshore platform and provide feedback to the coordinated control system. The coordinated control system then controls the actuation of the actuators through calculation to maintain the stability of the connection points between the motion compensation devices and the connecting arms, so that the upper modules can be stably lifted under the action of the connecting arms.

[0018] Step 2.3: When the load transfer of the upper assembly is completed, the two crane vessels continue to unload and drain water synchronously to completely separate the upper assembly from the jacket;

[0019] Step 2.4: The laser ranging sensor on the connecting arm detects the distance between the upper assembly and the jacket. When the vertical distance between the bottom of the upper assembly and the jacket exceeds a set safety height, the two crane vessels stop unloading and simultaneously depart from the jacket.

[0020] Step 2.5: After the operation in step 2.4 is completed, the transport ship slowly moves to the bottom of the upper assembly carried by the two crane ships. The two crane ships increase the draft of the crane ships by loading ballast water tanks, completing the load transfer of the upper assembly and the connecting arm from the crane ships to the transport ship.

[0021] Step 2.6: The crane ship increases its draft by loading the water tank, the motion compensation device completely detaches from the connecting arm, and the thrust device is started again to control the crane ship and the transport ship to reach a safe distance. The transport ship completes the transportation task, and the offshore platform dismantling operation is completed.

[0022] Improvement on the above technical solution: before dismantling the upper assembly, the tonnage of the crane vessel that matches the size of the offshore platform is independently selected.

[0023] Further improvement to the above technical solution: before the upper assembly is dismantled, the length of the connecting arm is determined to match the size of the offshore platform, and the connection point between the connecting arm and the motion compensation device is adjusted according to operational requirements.

[0024] Further improvement to the above technical solution: during the process of dismantling the upper assembly, the two crane ships and the four motion compensation devices are connected by the two connecting arms to form an integral structure.

[0025] A further improvement to the above technical solution: The motion compensation device comprises three actuators forming a three-dimensional motion compensation device. The lower ends of the actuators are fixed to the crane vessel, and the upper ends of the three actuators are concentrated at a point, achieving movement in three directions in space. This facilitates compensating for the impact of the crane vessel's movement on the connecting arm and the upper assembly during offshore platform dismantling operations.

[0026] Compared with the prior art, the advantages and positive effects of the present invention are:

[0027] The present invention installs motion compensation devices on two conventional crane ships, and uses the lifting arm to lift the upper module as a whole for integrated separation and demolition. The lifting arm length and the installation position of the motion compensation device can be selected and adjusted according to the scale of the operation object, and the multiple degrees of freedom generated by the environmental load on the ship during the demolition operation can be compensated, thereby ensuring the stability of the upper module during the demolition process, expanding the operation window, and eliminating the need for large floating cranes or special floating operation ships, thereby significantly reducing demolition costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of a three-dimensional motion compensation device used in a dual-vessel floating offshore platform dismantling method of the present invention;

[0029] Figure 2 A schematic diagram of a crane vessel equipped with a motion compensation device used in a dual-vessel floating offshore platform dismantling method according to the present invention;

[0030] Figure 3 This is a general schematic diagram of the dual-vessel floatation motion compensation demolition system of the present invention;

[0031] Figure 4 Schematic diagram of step 1.4 in a dual-vessel floating offshore platform dismantling method according to the present invention;

[0032] Figure 5 Schematic diagram of step 1.6 in a dual-vessel floating offshore platform dismantling method according to the present invention;

[0033] Figure 6 Schematic diagram of step 2.3 in a dual-vessel floating offshore platform dismantling method according to the present invention;

[0034] Figure 7 Schematic diagram of step 2.4 in a dual-vessel floating offshore platform dismantling method according to the present invention;

[0035] Figure 8 Schematic diagram of step 2.5 in a dual-vessel floating offshore platform dismantling method according to the present invention;

[0036] Figure 9This is a schematic diagram of step 2.6 in a dual-vessel floating offshore platform dismantling method according to the present invention.

[0037] In the figure: 1. Motion compensation device; 2. Crane vessel; 3. Upper assembly; 4. Connecting arm; 5. Jacket; 6. Transport vessel; 101. Ball joint; 102. Hydraulic cylinder; 103. Ball joint seat; 104. Compensation platform base; 105. Attitude sensor; 201. Crane; 202. Hook. Implementation Method

[0038] In order to further understand the content, features and effects of the present invention, the following examples are listed and described in detail with reference to the accompanying drawings:

[0039] See also Figures 1-8 The present invention provides an embodiment of a method for dismantling a dual-vessel floating offshore platform. The offshore platform comprises a jacket 5 and an upper assembly 3. During the dismantling of the upper assembly 3, a transport vessel 6 and two crane vessels 2 are used. The two crane vessels 2 are equipped with a coordinated dynamic positioning system, a displacement control system, and two connecting arms 4. A laser ranging sensor is installed on the connecting arms 4. The laser ranging sensor is used to detect the distance between the upper assembly 3 and the jacket 5. The two crane vessels 2 are respectively equipped with a ballast water tank, a side thruster, two large cranes, and two motion compensation devices 1. The motion compensation device 1 includes a posture sensor 105, an actuator, and a ball joint 101 connecting the crane vessel 2 and the connecting arm 4. The two large cranes are used to lift the two connecting arms 4. The two ends of the connecting arm 4 are used to connect to the two motion compensation devices 1 on the two crane vessels 2, respectively. The method for dismantling the upper assembly 3 of the offshore platform comprises the following construction steps:

[0040] Step 1: Before dismantling the upper block 3, the following tasks must be completed:

[0041] Step 1.1: The offshore platform has completed the wellhead abandonment work, and a suitable climate window is selected to prepare for the removal of the upper module 3 of the offshore platform;

[0042] Step 1.2: Select a matching connecting arm 4 according to the size of the demolished offshore platform, and determine the installation position of the motion compensation device 1 on the deck of the crane vessel 2;

[0043] Step 1.3: Two crane vessels 2 are respectively arranged on either side of the offshore platform. The draft of the crane vessels 2 is adjusted simultaneously to ensure that the upper end support points of the motion compensation devices 1 are at the same level, and the connecting arm 4 remains horizontal and the upper surface of the connecting arm 4 is lower than the bottom surface of the offshore platform. The collaborative dynamic positioning system calculates the operating position, and the collaborative dynamic positioning system ensures the collaborative accuracy of the two crane vessels 2 during the operation.

[0044] Step 1.4: A crane vessel 2 is equipped with two large cranes on its side. The large cranes include a crane 201 and a hook 202. The two large cranes operate to lift two connecting arms 4. One end of each connecting arm 4 is connected to a corresponding motion compensation device 1 on the same crane vessel 2 via a spherical joint 101 installed at the top of the motion compensation device 1. The connecting arms 4 are aligned vertically with the crane vessel 2 and the centerline of the two crane vessels 2.

[0045] Step 1.5: The two crane vessels 2 move toward the offshore platform through the displacement control system, and the speed of the thrusters is adjusted by the coordinated positioning system to ensure that the two crane vessels 2 have the same speed during the approach process;

[0046] Step 1.6: When the two crane vessels 2 reach the designated location, the other ends of the two connecting arms 4 are connected to the corresponding two motion compensation devices 1 on the other crane vessel 2. The large crane releases the hooks connected to the connecting arms 4. The load of the connecting arms 4 is completely borne by the motion compensation devices 1 installed on the decks of the two crane vessels 2.

[0047] Step 1.7: The crane vessel 2 reduces its draft by discharging loads from the ballast water tank, so that the top surfaces of the two connecting arms 4 contact the bottom surface of the upper assembly 3 and generate a certain pre-pressure;

[0048] Step 1.8: Cut and separate the upper assembly block 3 and the jacket 5.

[0049] Step 2: After completing the preparatory work before dismantling, start the overall dismantling operation of the upper block 3, including the following steps:

[0050] Step 2.1: Synchronously start the two crane vessels 2 to unload and drain water, controlling the unloading speed to be the same, so that the load of the upper module 3 is gradually transferred from the jacket 5 to the two connecting arms 4;

[0051] Step 2.2: The two connecting arms 4 are connected to the two crane vessels 2 via the motion compensation device 1. The crane vessels 2 and connecting arms 4 are equipped with attitude sensors 105. The attitude sensors 105 measure the posture changes of the crane vessels 2 and connecting arms 4 during the removal of the upper block 3 and feed them back to the coordinated control system. The actuators are then controlled by calculation to maintain the stability of the connection point between the motion compensation device 1 and the connecting arms 4, so that the upper block 3 can be stably lifted under the action of the connecting arms 4.

[0052] Step 2.3: When the load transfer of the upper assembly 3 is completed, the two crane vessels 2 continue to unload and drain water synchronously, so that the upper assembly 3 is completely separated from the jacket 5;

[0053] Step 2.4: The laser distance sensor on the connecting arm 4 detects the distance between the upper assembly 3 and the jacket 5. When the vertical distance between the bottom of the upper assembly 3 and the jacket 5 exceeds the set safety height, the two crane vessels 2 stop unloading and simultaneously move away from the jacket 5.

[0054] Step 2.5: After the operation in step 2.4 is completed, the transport ship 6 slowly moves to the bottom of the upper assembly 3 carried by the two crane ships 2. The two crane ships 2 increase their draft by loading ballast water tanks, completing the load transfer of the upper assembly 3 and the connecting arm 4 from the crane ship 2 to the transport ship 6;

[0055] Step 2.6: The crane vessel 2 increases its draft through the ballast water tank, the motion compensation device 1 is completely separated from the connecting arm 4, and the thrust device is started again to control the crane vessel 2 and the transport ship 6 to reach a safe distance. The transport ship 6 completes the transportation task, and the offshore platform dismantling operation is completed.

[0056] Furthermore, before dismantling the upper assembly 3, a matching crane vessel 2-ton capacity is selected based on the size of the offshore platform. Before dismantling the upper assembly 3, the length of the connecting arm 4 is determined to match the size of the offshore platform, and the connection point between the connecting arm 4 and the motion compensation device 1 is adjusted according to the operational requirements.

[0057] Furthermore, during the process of dismantling the upper assembly 3 , the two crane vessels 2 and the four motion compensation devices 1 are connected via two connecting arms 4 to form an integral structure.

[0058] Specifically, the aforementioned motion compensation device 1 comprises three actuators, each of which is a three-dimensional motion compensation device. The lower ends of the actuators are fixed to the crane vessel 2, while the upper ends of the three actuators converge at a single point, achieving three-dimensional motion. This facilitates compensating for the effects of the crane vessel 2's movement on the connecting arm 4 and upper assembly 3 during the offshore platform dismantling operation. The actuators are hydraulic cylinders, and a compensation platform base 104 is mounted on the deck of the crane vessel 2. A spherical joint 103 is mounted on the compensation platform base 104. The lower ends of the three hydraulic cylinders are hinged to the spherical joint 103 via spherical joints.

[0059] Although the above description of the method for dismantling an offshore platform proposed by the present invention has been made in conjunction with an embodiment, the present invention is not limited to the specific embodiments mentioned above. Without departing from the spirit of the present invention and the scope of protection of the claims, changes including but not limited to the structure and form of the components involved in the present invention should be deemed to fall within the scope of protection of the present invention.

Claims

1. A method for dismantling a dual-vessel floating offshore platform, wherein the offshore platform comprises a jacket and an upper assembly, characterized in that: During the removal of the upper assembly, a transport ship and two crane ships are used. The two crane ships are equipped with a coordinated dynamic positioning system, a displacement control system and two connecting arms. The connecting arms are equipped with a laser ranging sensor, which is used to detect the distance between the upper assembly and the jacket. The two crane ships are respectively equipped with a ballast water tank, a side thruster, two large cranes and two motion compensation devices. The motion compensation devices include an attitude sensor, an actuator and a ball joint connecting the crane ship and the connecting arms. The two large cranes are used to lift the two connecting arms. The two ends of the connecting arms are used to connect to the two motion compensation devices on the two crane ships respectively. The method for removing the upper assembly of the offshore platform includes the following construction steps: Step 1: The following work must be completed before dismantling the upper assembly: Step 1.1: The offshore platform has completed the wellhead abandonment work, and a suitable climate window is selected to prepare for the upper module removal operation of the offshore platform; Step 1.2: Select a matching connecting arm according to the size of the offshore platform to be dismantled and determine the installation position of the motion compensation device on the deck of the crane vessel; Step 1.3: The two crane vessels are respectively arranged on either side of the offshore platform. The drafts of the crane vessels are adjusted simultaneously to ensure that the upper support points of the motion compensation devices are at the same level, and that the connecting arms remain horizontal and their upper surfaces are lower than the bottom surface of the offshore platform. The collaborative dynamic positioning system calculates the operating position, and the collaborative dynamic positioning system ensures the coordinated accuracy of the two crane vessels during the operation. Step 1.4: Two large cranes are installed on the side of a crane ship. The two large cranes are used to lift the two connecting arms. One end of each connecting arm is connected to the corresponding motion compensation device on the same crane ship via a ball joint installed on the top of the motion compensation device. The connecting arm is vertically aligned with the crane ship and the centerline of the two crane ships. Step 1.5: The two crane vessels move toward the offshore platform through the displacement control system, and the coordinated dynamic positioning system adjusts the rotation speed of the thrusters to ensure that the two crane vessels have the same speed during the approach process; Step 1.6: When the two crane vessels arrive at the designated location, the other ends of the two connecting arms are respectively connected to the corresponding two motion compensation devices on the other crane vessel, and the large crane releases the hooks connected to the connecting arms. The load of the connecting arms is completely borne by the motion compensation devices installed on the decks of the two crane vessels; Step 1.7: The crane vessel reduces its draft by discharging loads through the ballast water tank, so that the top surfaces of the two connecting arms contact the bottom surface of the upper assembly and generate a certain pre-pressure; Step 1.8: Cutting and separating the upper assembly block from the jacket; Step 2: After completing the preparatory work before demolition, start the overall demolition of the upper module, including the following steps: Step 2.1: Synchronously start the two crane vessels to unload and drain water, controlling the unloading speed to be the same, so that the load of the upper module is gradually transferred from the jacket to the two connecting arms; Step 2.2: The two connecting arms are connected to the two crane vessels via motion compensation devices. The crane vessels and connecting arms are equipped with attitude sensors. The attitude sensors measure the changes in the positions of the crane vessels and connecting arms during the removal of the upper module of the offshore platform and provide feedback to the coordinated control system. The actuators are then controlled by calculation to maintain the stability of the connection points between the motion compensation devices and the connecting arms, so that the upper module can be stably lifted under the action of the connecting arms. Step 2.3: When the load transfer of the upper assembly is completed, the two crane vessels continue to unload and drain water synchronously to completely separate the upper assembly from the jacket; Step 2.4: The laser ranging sensor on the connecting arm detects the distance between the upper assembly and the jacket. When the vertical distance between the bottom of the upper assembly and the jacket exceeds a set safety height, the two crane vessels stop unloading and simultaneously depart from the jacket. Step 2.5: After the operation in step 2.4 is completed, the transport ship slowly moves to the bottom of the upper assembly carried by the two crane ships. The two crane ships increase the draft of the crane ships by loading ballast water tanks, completing the load transfer of the upper assembly and the connecting arm from the crane ships to the transport ship. Step 2.6: The crane vessel increases its draft by loading the ballast water tank, the motion compensation device completely detaches from the connecting arm, and the thrust device is started again to control the crane vessel and the transport ship to reach a safe distance. The transport ship completes the transportation task, and the offshore platform dismantling operation is completed.

2. The method for dismantling a dual-vessel floating offshore platform according to claim 1, characterized in that: Before dismantling the upper assembly, the tonnage of the crane vessel that matches the size of the offshore platform is independently selected.

3. The method for dismantling a dual-vessel floating offshore platform according to claim 1 or 2, characterized in that: Before dismantling the upper assembly, the length of the connecting arm is determined to match the size of the offshore platform, and the connection point between the connecting arm and the motion compensation device is adjusted according to operational requirements.

4. The method for dismantling a dual-vessel floating offshore platform according to claim 1 or 2, characterized in that: During the process of dismantling the upper assembly, the two crane ships and the four motion compensation devices are connected by the two connecting arms to form an integral structure.

5. The method for dismantling a dual-vessel floating offshore platform according to claim 3, characterized in that: During the process of dismantling the upper assembly, the two crane ships and the four motion compensation devices are connected by the two connecting arms to form an integral structure.

6. The method for dismantling a dual-vessel floating offshore platform according to claim 1 or 2, characterized in that: The motion compensation device is composed of three actuators to form a three-dimensional motion compensation device. The lower end of the actuator is fixed to the crane ship, and the upper ends of the three actuators are concentrated at one point to achieve movement in three directions of space.

7. The method for dismantling a dual-vessel floating offshore platform according to claim 3, characterized in that: The motion compensation device is composed of three actuators to form a three-dimensional motion compensation device. The lower end of the actuator is fixed to the crane ship, and the upper ends of the three actuators are concentrated at one point to achieve movement in three directions of space.

8. The method for dismantling a dual-vessel floating offshore platform according to claim 5, characterized in that: The motion compensation device is composed of three actuators to form a three-dimensional motion compensation device. The lower end of the actuator is fixed to the crane ship, and the upper ends of the three actuators are concentrated at one point to achieve movement in three directions of space.

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