A two-section method for removing a hundred-meter deep double-layer riser

Abstract

The application discloses a two-section type removing method for a double-layer riser with a water depth of 100 meters, which is divided into three stages, namely, platform equipment layout, submersible underwater pipe cutting and riser cutting and ship crane lifting and moving the riser. The application adopts a method of cutting only one time to remove and lift the double-layer riser in a two-section type, so that the frequency of submersible underwater operation is greatly reduced, the ship time is saved, the ship standby caused by the on-site weather standby is avoided, the cost is reduced and the efficiency is increased, meanwhile, in the construction, the pipe sections with large depth difference are treated by adopting a single-point observation, multi-beacon correction and multi-point safe suspension and the like, and the upper and lower risers after being cut are respectively discarded by cooperation of the air submersible, the saturation and the ROV, so that the absolute safety of the construction personnel, the equipment and the platform is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of standpipe removal in offshore oil engineering, and particularly to a two-section type removal method for a double-layer standpipe in a hundred-meter water depth. BACKGROUND

[0002] Many offshore platforms have been in service for many years, in order to improve the platform integrity and safety, the platform is lightened and extended in service life, and the unnecessary standpipe is often abandoned and removed. The conventional operation method for standpipe removal is to cut the standpipe into multiple sections and hoist.

[0003] Each cutting is immediately hoisted back by the ship crane, and the diver needs to dive multiple times to cut the standpipe, and then the ship crane is used to lower the rigging for hoisting and transferring. If the standpipe removal is carried out in a water depth of more than 100 meters, the number of days required for diving operation and the number of days required for the main operation ship are large, and the diving operation and hoisting operation are greatly affected by weather and sea conditions, which is easy to cause weather standby. SUMMARY

[0004] The two-section type removal method for a double-layer standpipe in a hundred-meter water depth disclosed by the present application is used for fixed platform standpipe removal operation, and only one cut is made at the position of the standpipe in a water depth of 40 meters, the underwater cutting workload is reduced, the underwater transmission hoisting workload is reduced, and two sections are transmitted, which greatly reduces the construction amount, optimizes the construction procedure, saves the engineering ship days, and realizes cost reduction and efficiency increase.

[0005] In order to solve the above technical problems, the present application provides a two-section type removal method for a double-layer standpipe in a hundred-meter water depth, which is completed through the following steps:

[0006] S1, the winch steel wire rope path is arranged above the position of the standpipe, and is guided by an A-frame, an ear, and a pulley in the middle;

[0007] S2, a hoisting flange used for matching the upper end flange of the upper section standpipe is prefabricated, and three hoisting rigging hoisting clamps are prefabricated for connection;

[0008] S3, the platform winch steel wire rope is connected with the hoisting flange prefabricated in advance at the port of the upper section standpipe;

[0009] S4, the empty diving equipment is arranged, the path between the diving basket and the decompression chamber is not isolated, the diving basket is installed close to the side of the ship, and the installation is easy to enter and exit the water, the delivery steel wire rope winch needs to be tested for tension, and the diving basket needs to be tested for static load;

[0010] S5, the empty diving into water cuts the suspension clamp above the position of the standpipe in a water depth of 40 meters, the upper section standpipe is fixed after being bound, and then the suspension clamp is cut, and the suspension clamp is hoisted together with the standpipe after being cut;

[0011] S6. Drill a hole 500mm below the cutting point of the empty potential, install limit bolts to prevent the inner tube of the double-layer pipe from slipping and the hoisting clamp from slipping, and install the hoisting clamp below the drilling position.

[0012] S7. The air-diving submersible installs a diamond wire cutter at the 40-meter underwater riser cutting point. The platform winch is tensioned, and the hydraulic equipment of the diamond wire cutter is activated on the platform deck. The air-diving submersible moves away from the cutting point to observe. When the diamond wire appears on the other side of the upper riser, the platform deck stops the hydraulic equipment, and the air-diving submersible approaches the cutting point to observe the riser cutting status.

[0013] S8. The aerial submersible prepares the rigging on the deck according to the upper section riser hoisting rigging diagram. After entering the water, it installs the hoisting rigging at the upper section riser hoisting point. To prevent the hoisting rigging from swaying and getting tangled with the grouting pipeline of the platform guide frame, floats are installed at the hoisting slings.

[0014] S9. The ROV connects the rigging pre-installed on the upper riser section to the rigging of the main work vessel crane. The main work vessel is under load, and the crane slowly pulls back the wire rope. The platform winch wire rope is slowly slack and lowered. The main work vessel pulls upward and outward on the platform. After the platform winch is no longer under load, the ROV disconnects from the platform winch. The platform winch is then pulled back. At this time, the crane transfers the upper riser section from a vertical position to a horizontal position. The main work vessel moves the vessel more than 500 meters away from the platform to wet-store the upper riser section.

[0015] S10. After the upper section of the riser is removed, the lifting clamps pre-installed on the lower section of the riser below the cutting point are used for saturation diving operations. The platform winch wire rope and lifting slings are connected. The platform winch is kept under tension and the tension should be the maximum dynamic load of the lower section of the riser.

[0016] S11. After the upper section of the riser is removed, the riser hanging clamps left on the guide frame are retrieved by air diving, and the first riser hanging clamp of the lower section of the riser is opened.

[0017] S12. Saturation diving into the water, remove the hanging clamps of the lower section of the riser, and formulate a saturation diving depth plan based on the water depth of the pipe clamps; the first and last riser hanging clamps of the lower section of the riser are not cut but opened to support the load of the lower section of the riser. The first one is opened by empty diving, and then the remaining riser hanging clamps are removed from top to bottom.

[0018] S13. Saturated diving to remove the flange connecting the riser and the expansion bend. The main work vessel places a counterweight on the seabed. The winch wire rope of the main work vessel is connected to the bottom of the riser through the pulley on the counterweight. The rigging is tightened to prevent the riser from swinging and colliding with the guide frame during the transfer. During the transfer, the winch is used to raise and lower the riser in coordination with the ship's crane to complete the riser hoisting and transfer operation.

[0019] S14. The ROV connects the rigging pre-installed on the lower riser section to the rigging of the main work vessel crane. The ROV monitors the entire process of lower riser installation underwater and carries hydraulic shears into the water to cut the winch wire rope in case of emergency. During the lower riser installation, after the main work vessel has reached the desired position, the ROV disconnects the platform winch wire rope from the lower riser.

[0020] S15. When the crane is lifting and moving the lower section of the riser, after the load is applied, the ship should move 10m away from the platform. The crane operator should pay attention to the load on the crane gradually increasing to the maximum dynamic load value. If it exceeds the maximum dynamic load value, the platform winch and the main ship winch should loosen the wire rope until it is no longer under load. If it still exceeds the maximum dynamic load value, the ROV should use hydraulic shears to cut the wire rope.

[0021] Furthermore, in step S5, to prevent the upper section of the riser from collapsing due to stress release, the upper section of the riser and the guide frame structure need to be tied together with a chain hoist before cutting. After cutting the suspension clamps, the riser is released, and the two middle suspension clamps are left open but not cut as load-bearing supports for the riser. The upper section of the riser is then hoisted and then cut and recycled.

[0022] Furthermore, due to the water depth limitations of the underwater submersible operation, the riser was cut at a depth of 40 meters. The upper section of the riser was relatively short, so a vertical-to-horizontal hoisting method could be adopted. The lower section of the riser was 76 meters long. If a diagonal vertical-to-horizontal hoisting method were adopted, the hoisting stress on the lower section of the riser would be too great, which would cause interference with the jacket. To ensure successful hoisting, a single-point vertical hoisting method was adopted. When the crane on the main work vessel was hoisting the relocated riser section, after disconnecting from the platform, the vessel was slowly moved to a predetermined area more than 500 meters away from the platform to place the riser.

[0023] Furthermore, in step S13, in order to prevent the lower riser from collapsing due to the release of pressure, the lower riser section and the guide frame structure need to be tied together with a chain hoist before cutting. After cutting the pipe clamp, the lower riser section is released. The remaining riser clamps are first tied and fixed to the riser before cutting. After cutting, the clamps are hoisted together with the riser.

[0024] The technical advantages of this invention are as follows: This invention provides a method for dismantling two-section risers in water depths of 100 meters. It employs a single-cut, two-section dismantling and hoisting method for double-layer risers, significantly reducing the number of dives and saving ship days. It avoids ship downtime caused by weather conditions, achieving cost reduction and efficiency improvement. Furthermore, during construction, for pipe sections with significant depth differences, single-point observation, multiple beacon calibration, and multiple safety suspension methods are employed. The combination of air-diving, saturation, and ROV (Remotely Operated Vehicle) ensures the absolute safety of personnel, equipment, and the platform by disposing of the separated upper and lower risers. The feasibility of the construction plan has been verified and successfully implemented in practice. This two-section construction method optimizes the dismantling steps for double-layer risers in water depths exceeding 100 meters, saving diving and ship days, achieving cost reduction and efficiency improvement, and providing valuable experience for subsequent offshore riser dismantling. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the dismantling and layout of the platform of the present invention.

[0026] Figure 2 This is a schematic diagram of frame A of the present invention.

[0027] Figure 3 This is a schematic diagram of the riser hoisting clamp of the present invention.

[0028] Figure 4 This is a schematic diagram of the winch connecting the upper section of the riser in this invention.

[0029] Figure 5 This is a schematic diagram of the hoisting slings for the upper section of the riser in this invention.

[0030] Figure 6 This is a schematic diagram of the transmission of the upper section of the riser in this invention.

[0031] Figure 7 This is a schematic diagram of the winch connecting the lower section of the riser in this invention.

[0032] Figure 8 This is a schematic diagram showing the connection between the counterweight and the lower end of the riser in this invention.

[0033] Figure 9 This is a schematic diagram of the hoisting of the lower section of the riser pipe according to the present invention. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0035] This invention provides a two-stage dismantling method for double-layer risers in water depths of 100 meters, such as... Figures 1-9 As shown, this can be completed through the following steps:

[0036] The winch wire rope is arranged above the riser, with an A-frame (such as...) passing through the middle. Figure 2 As shown), the lugs and pulleys guide the movement. Figure 1 As shown; note the interference between the wire rope path and the platform structure, pipelines, and cables; after the winch is welded and fixed, the weld points need to be inspected by NDT, and a tensile test should be conducted based on a factor of 1.25 times the maximum load required to transmit the riser section.

[0037] Prefabricate lifting flanges to match the upper flange of the upper riser, and prefabricate 3 lifting clamps for connecting lifting slings.

[0038] like Figure 4 As shown, the platform winch wire rope is connected to a pre-fabricated lifting flange at the upper section of the riser, used for lifting and transferring the upper section of the riser. In some other embodiments, if the flange at the upper section of the riser is severely corroded, a lifting clamp is installed below the flange and connected to the winch wire rope.

[0039] The riser platform section is cut in advance by the suspended clamp when the riser needs to be transferred.

[0040] The layout of the underwater equipment site lacks isolation between the diving basket and the decompression chamber; the diving basket is installed close to the hull side, in a location easily accessible for entry and exit from the water; the delivery wire rope winch must undergo a tensile test, and the diving basket must undergo a static load test; all welded and fixed equipment must undergo NDT inspection, such as... Figure 1 As shown.

[0041] The underwater submersible cutter cuts the suspension clamps at a depth of over 40 meters on the riser. First, the upper section of the riser is secured, and then the suspension clamps are cut. After cutting, the suspension clamps are hoisted together with the riser. At the same time, to prevent the upper section of the riser from collapsing due to stress release, the upper section of the riser is also tied to the guide frame structure with a chain hoist before cutting. After cutting the suspension clamps, the riser is released, leaving the two middle suspension clamps open but not cut, as they serve as load-bearing supports for the riser. The upper section of the riser is hoisted and then cut and retrieved.

[0042] Drill a hole 500mm below the potential cutting point and install limit bolts to prevent slippage of the inner pipe of the double-layered pipe and slippage of the lifting clamp. Install the lifting clamp below the drilled hole. Figure 7 .

[0043] The air-diving submersible installs a diamond wire cutter at the riser cutting point 40 meters underwater. The platform winch is tensioned, and the hydraulic system for the diamond wire cutter is activated on the platform deck. The air-diving submersible moves away from the cutting point to observe. When the diamond wire appears on the other side of the upper riser, the platform deck stops the hydraulic system, and the air-diving submersible approaches the cutting point to observe the riser cutting status.

[0044] like Figure 5As shown, the aerial submersible prepares the rigging on the deck according to the upper section riser hoisting rigging diagram. After entering the water, it installs the hoisting rigging at the upper section riser hoisting point. To prevent the hoisting rigging from swaying and getting tangled with the grouting pipeline of the platform guide frame, floats are installed at the hoisting rigging lifting rings.

[0045] At this time, the working vessel is close to the platform's riser leg, and the vessel is perpendicular to the leg at a 90-degree angle, with the vessel's crane and the leg on the same plane.

[0046] like Figure 6 As shown, the ROV connects the rigging pre-installed on the riser to the rigging of the main work vessel crane. The main work vessel is under load, and the crane slowly pulls back the wire rope. The platform winch wire rope is slowly slackened and lowered. The main work vessel pulls upward and outward on the platform. After the platform winch is no longer under load, the ROV disconnects from the platform winch, and the platform winch is retrieved. At this time, the crane transfers the upper riser section from a vertical position to a horizontal position. The main work vessel moves the vessel more than 500 meters away from the platform to wet-store the upper riser section.

[0047] like Figure 7 As shown, after the upper section of the riser is removed, the top of the lower section of the riser below the cutting point is pre-installed with a hoisting clamp, and the platform winch wire rope and hoisting sling are connected.

[0048] During saturation submersion operations, the platform winch should be kept under tension, with the tension being the maximum dynamic load of the lower riser section.

[0049] After the upper section of the riser is removed, the remaining riser hanging clamps on the guide frame are retrieved by air submersion, and the first riser hanging clamp of the lower section is opened to avoid saturation and depressurization, which would then be used to open and cut the riser, thus saving time.

[0050] For saturation diving, remove the lower section of the riser's suspension clamps. Develop a saturation diving depth plan based on the water depth of the suspension clamps. The first and last suspension clamps of the lower riser section are opened without cutting; they are used to support the lower riser's load. The first suspension clamp is opened during a dry dive. Then, remove the remaining riser suspension clamps from top to bottom. When opening the last riser suspension clamp, to prevent potential breakage due to stress release in the lower riser section, the lower riser section must be secured to the jacket structure using chain hoists before cutting. Release the lower riser section after cutting the clamps. The remaining riser clamps are first secured to the riser before cutting. After cutting, the clamps are hoisted together with the lower riser section.

[0051] like Figure 8 As shown, the saturated diving vessel removes the flange connecting the riser and the expansion bend. The main work vessel places a counterweight on the seabed. The winch wire rope of the main work vessel is connected to the bottom of the riser through the pulley on the counterweight. The rigging is tightened to prevent the lower riser from swinging and colliding with the guide frame during the transfer of the lower riser section. During the transfer process, the winch is used in conjunction with the ship's crane to complete the riser hoisting and transfer operation.

[0052] The ROV connects the rigging pre-installed on the lower riser section to the crane rigging on the main work vessel.

[0053] The ROV provides underwater monitoring throughout the lower riser installation process and carries hydraulic shears to cut the winch wire rope in case of emergencies.

[0054] During the hoisting of the lower section of the riser, after the main work vessel is in position with force, the ROV disconnects the platform winch wire rope from the riser.

[0055] When the crane is lifting and moving the lower section of the riser, after the load is applied, the ship should move 10m away from the platform. The crane operator should pay attention to the load on the crane gradually increasing to the maximum dynamic load value. If it exceeds the maximum dynamic load value, the platform winch and the main ship winch should loosen the wire rope until it is no longer under load. If it still exceeds the maximum dynamic load value, the ROV should use hydraulic shears to cut the wire rope.

[0056] Due to the water depth limitations of underwater submersible operations, the riser was cut at a depth of 40 meters. Since the upper section of the riser is relatively short, a vertical-to-horizontal hoisting method can be used, such as... Figure 6 As shown; the lower riser section is 76 meters long. If the inclined vertical-to-horizontal hoisting method is adopted, the hoisting stress on the lower riser section will be too large, which will cause interference with the guide frame. To ensure successful hoisting, a single-point vertical hoisting method will be adopted, such as... Figure 9 As shown; when the main work vessel crane lifts the relocated riser section, after disconnecting from the platform, the vessel slowly moves to a predetermined area more than 500 meters away from the platform to place the riser.

[0057] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A two-section method for removing a 100-meter-deep double-layer riser, which is characterized by the following steps: S1. The winch steel wire rope path is arranged above the riser position, and the path is guided by an A-frame, an ear, and a pulley; S2. A hoisting flange is prefabricated for matching the upper end flange of the upper riser section, and three hoisting rigging hoisting clamps are prefabricated for connection; S3. The platform winch steel wire rope is connected to the hoisting flange prefabricated in advance at the riser section port; S4. The air diving equipment is arranged, and there is no isolation between the diving basket and the decompression chamber. The diving basket is installed near the side of the ship, which is easy to enter and exit the water. The delivery steel wire rope winch must be subjected to a tension test, and the diving basket must be subjected to a static load test; S5. The air diving enters the water to cut the suspension clamp above the 40-meter-deep position of the riser underwater. After the upper riser section is fixed by binding, the suspension clamp is cut. After cutting, the suspension clamp is hoisted together with the riser; S6. The air diving drills a hole 500 mm below the cutting point and installs a limiting bolt to prevent the inner tube of the double-layer pipe from slipping and the hoisting clamp from slipping, and installs a hoisting clamp below the drilling position; S7. The air diving installs a diamond wire cutting tool at the 40-meter-deep riser cutting point underwater, the platform winch is tensioned, the platform deck starts the hydraulic equipment of the diamond wire cutting tool, the air diving is away from the cutting point for observation, when the diamond wire appears on the other side of the upper riser section, the platform deck stops the hydraulic equipment, and the air diving approaches the cutting point to observe the riser cutting state; S8. The air diving arranges the rigging according to the hoisting rigging diagram of the upper riser section on the deck, installs the hoisting rigging at the hoisting point of the upper riser section after entering the water, and installs a floating ball at the hoisting rigging ring to prevent the hoisting rigging from being entangled with the platform guide pipe pile grouting pipeline; S9. The ROV disconnects the rigging pre-installed on the upper riser section by the air diving and the main work ship hoist rigging, the main work ship is tensioned, the main work ship hoist slowly recovers the steel wire rope, the platform winch slowly relaxes and is lowered, the main work ship is tensioned upwards and to the outside of the platform, the platform winch is not tensioned, the ROV disconnects the platform winch, the platform winch recovers the steel wire rope, the hoist at this time transfers the upper riser section from the vertical state to the horizontal state, and the main work ship moves away from the platform by 500 meters to store the upper riser section wetly; S10. After the upper riser section is removed, the air diving installs the prefabricated hoisting clamp on the lower riser section below the cutting point and connects the platform winch steel wire rope and the hoisting rigging, the saturation diving enters the water for work, and the platform winch is always kept tensioned. The tension should be the maximum dynamic load of the lower riser section; S11. After the upper riser section is removed, the air diving recovers the riser suspension clamp left on the guide pipe pile and opens the first riser suspension clamp of the lower riser section; S12. The saturation diving enters the water, removes the riser suspension clamp of the lower riser section, and formulates a saturation diving depth plan according to the water depth of the suspension clamp. The first and last riser suspension clamps of the lower riser section are not cut but opened, which are used to support the load of the lower riser section, and the first one is opened by the air diving, and then the remaining riser suspension clamps are removed from top to bottom. S13, the saturation diving removes the riser and the expansion bend flange, the main work ship places the counterweight on the seabed, the main work ship winch steel wire rope is connected with the riser bottom through the counterweight pulley, with the tight harness, prevents the riser from colliding with the guide pipe frame during transmission, and completes the riser lifting and transfer operation through the winch and the ship crane during transmission; S14, the ROV disconnects the empty submersible pre-installed on the lower riser harness and the main work ship crane harness, the ROV monitors the whole process underwater during the lower riser lifting, and carries hydraulic tongs into the water, which is used for emergency cutting of the winch steel wire rope, during the lower riser lifting, the main work ship brings the force into place, and the ROV releases the platform winch steel wire rope and the lower riser; S15, when the crane hoists and moves the lower riser, the ship cooperates to move away from the platform by 10m, the crane operator needs to pay attention to whether the load borne by the crane exceeds the maximum dynamic load value, if it exceeds, the platform winch and the main ship winch loosen the steel wire rope to no force, if it still exceeds, the ROV uses hydraulic shears to cut the steel wire rope.

2. The two-stage removal method of a hundred-meter water depth double-wall riser according to claim 1, characterized in that: In step S5, to prevent the collapse phenomenon of the upper riser caused by the release of the possible force, the upper riser and the guide pipe frame structure are bound together by the chain before cutting, the riser is released after cutting the hanging clamp, and the middle two hanging clamps are only opened and not cut, as the riser bearing support, the upper riser is hoisted and then cut and recovered.

3. The two-stage removal method of a hundred-meter water depth double-wall riser according to claim 1, characterized in that: Due to the water depth limit of the empty submersible operation, the riser is cut at the underwater 40m position, the upper riser is short, and the vertical lifting method is adopted, the lower riser is 76m long, and the single-point vertical lifting method is adopted, the main work ship crane hoists and moves the riser section, and after the connection with the platform is released, the ship slowly moves to the predetermined area 500m away from the platform to place the riser.

4. The two-stage removal method of a hundred-meter water depth double-wall riser according to claim 1, characterized in that: In step S13, to prevent the collapse phenomenon of the lower riser caused by the release of the possible force, the lower riser and the guide pipe frame structure are bound together by the chain before cutting, the lower riser is released after cutting the hanging clamp, and the remaining hanging clamps are first bound and fixed with the riser before cutting, and the hanging clamps are hoisted with the riser after cutting.

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