WO1999022983A1

WO1999022983A1 - Rov installed suction piles

Info

Publication number: WO1999022983A1
Application number: PCT/EP1998/007012
Authority: WO
Inventors: William Henry Von Eberstein
Original assignee: Shell Internationale Research Maatschappij B.V.
Priority date: 1997-11-01
Filing date: 1998-10-30
Publication date: 1999-05-14
Also published as: NO20002236L; GB2350341B; NO20002236D0; BR9813332A; NO334253B1; ID23926A; OA11409A; GB0010174D0; GB2350341A

Abstract

A suction pile anchor system for anchoring offshore structures to the seabed is provided. The system includes a suction pile (10) having an upper end part provided with a pump valve for water to flow between the interior of the suction pile and the exterior thereof, and an ROV provided with pumping means connectable to the pump valve of the suction pile (10) and operable so as to induce water to flow between the interior of the suction pile and the exterior thereof.

Description

ROV INSTALLED SUCTION PILES

The present invention relates to a suction pile anchor system for securing offshore structures to the seabed. Such structures include for example floating offshore drilling and/or production vessels which must be maintained in position over a well site for offshore drilling operations and often for production operations. This often requires the deployment of an array of mooring lines, each anchored to the seabed with a pile foundation or the like. Installing such foundation elements for secure anchorage is time consuming and requires considerable offshore equipment.

Another problem arising m deepwater is that the spread of these mooring lines can be substantial and anchor structures are widely placed over a leasehold or even into adjacent lease blocks and the mooring arrays of adjacent blocks can overlap. Further, the sequential steps in development of such well site requires exploration wells, test wells, satellite subsea wells, etc., each of which can leave foundation elements in the seafloor so that the seafloor actually becomes crowded in relation to the necessary infrastructure for working offshore prospects .

Suction pile anchors as disclosed m U.S. Patent No. 4,318,641 have been known as an alternative to driving or drilling and grouting piles. These anchors provide opportunity for easier installation, but the installation of suction pile anchors in deepwater remains equipment intensive and does not facilitate foundation removal.

Thus, there remains a need for a method and system for anchoring offshore structures and vessels which facilitates ease of deployment with a minimum of equipmen .

In accordance with the invention there is provided a suction pile anchor system for anchoring offshore structures to the seabed, the system including a suction pile having an upper end part provided with a pump valve for water to flow between the interior of the suction pile and the exterior thereof; and an ROV provided with pumping means connectable to the pump valve of the suction pile and operable so as to induce water to flow between the interior of the suction pile and the exterior thereof.

By attaching the ROV to the suction pile to evacuate water from the suction pile, the pile can be installed in deepwater applications without requiring complicated equipment such as guidance wires for lowering a pump facility from a surface vessel to the suction pile. Furthermore, the suction pile can be adequately retrieved to surface by attaching the ROV to the suction pile and pumping fluid such as water or air into the suction pile so as to remove the suction pile from the seafloor.

Suitably said upper end part of the suction pile is further provided with a flood valve for water to enter the suction pile, the flood valve being operable by the ROV.

The suction pile is lowered into the water with the flood valve open. After the pile has reached the seabed and has partly penetrated the seabed under its own weight, the ROV closes the flood valve and attaches to the pump valve to evacuate water from the pile.

The invention will be described further m more detail and by way of example with reference to the accompanying drawings m which: Fig. 1 schematically shows a floating vessel anchored in accordance with the system of the invention;

Figs. 2 and 2A schematically show a suction pile anchor installed in the ocean floor in accordance with the invention; and

Figs. 3-22 schematically show various steps in the deployment of a suction pile anchor system in accordance with the invention.

Fig. 1 illustrates one application of the present invention. Here the suction pile anchors 10 secure a truss spar configuration mobile offshore drilling unit ("MODU") 12 m position over well site 14 at ocean floor 16. Each suction pile anchor is securely set within the ocean floor and is connected to MODU 12 through mooring or load lines 18. The use of taut line moorings may reduce the mooring spread. Further, buoys 20 may be included into the mooring lines .

Fig. 2 illustrates a suction pile anchor 10 installed in ocean floor 16. The suction pile anchor has a suction pile 22, here in the form of a cylinder having an open lower end and a closed upper end. A first load connection 24, here provided by load pad-eyes 24A, is provided on the side of the suction pile, positioned to be away from the ends of the suction pile and well below the mud line on deployment. Under load conditions with this configuration, the load will be resisted most efficiently by the ocean floor 16.

Flooding ports or valves 26 and pump or pressure port or valve 28 are provided through or adjacent the closed top of suction pile 22. Further, these valves are designed to be actuatable with a remotely operated vehicle ("ROV"), not shown. An installation connection is also provided at the top of the suction pile. Here the installation connection includes a lowering and lifting slmg 66. A load line or mam mooring wire extension 32 is connected to the first load connection 24 and provides an ROV operable second load line connection 34 above mudlme 16A of ocean floor 16. In Fig. 2, ma mooring wire extension 32 holds second load line connection 34 an accessible position through the inherent stiffness of the wire rope over short distances and a load line keeper or wire grabber latch 36.

Fig. 2A illustrates an alternative embodiment in which the accessibility of second load line connection 34 above the mudlme is secured with a buoy 38 attached to the mam mooring wire extension.

Fig. 3 illustrates the work deck of an anchor handling vessel 40 equipped to deliver and deploy four suction pile anchors 10 per excursion. The suction pile anchors are locked into cradles or transport slots 42 in which horizontal skids 44 provide stability for controlled deployment of the suction pile anchors. Wire 46 is spooled onto winches 41 provided on the deck of anchor handling vessel 40.

Fully loaded, the vessel travels to the installation site and the first suction pile anchor 10 is positioned for deployment. Preferably, this is with a two-way, hydraulically powered track roller assembly 43 which facilitates rapid, smooth suction pile positioning.

Referring to Fig. 4, the suction pile anchor smoothly rolls from the vessel, over stern roller 48, and into the water with flooding valves 26 open. At this stage, an overboardmg wire 58 supports the weight of suction anchor pile 10. After the anchor clears the stern roller, its weight is accepted by a deployment wire 59 connected to lowering and lifting sling 66 by an ROV operable connector 64, see Fig. 5. Descent of the suction pile anchor pauses at a shallow staging station below anchor handling vessel 40 and an ROV 60 is launched from the vessel to disconnect the overboarding hook from the sling .

Descent resumes and ROV 60 follows as suction pile anchor 10 is lowered to a bottom staging station point very near seafloor 16. The suction pile anchor has a tendency to rotate during descent and the ROV may need to properly orient suction pile anchor 10 such that first load connection 24 is aligned with the intended mooring line orientation. See Fig. 6. The suction pile anchor is then lowered for self-penetration under its own weight into the upper silt line of seafloor 16 and into clay muck. In this interval, the pay out of deployment were 59 is monitored so that it does not exceed the rate of self penetration.

At this point ROV 60 attaches itself to the top of suction pile anchor 10 and closes flooding valves 26. See Fig. 7. Continuing with Fig. 8, the ROV then engages pump valve 28 and pumps arranged within the ROV begin evacuating water from suction pile 10 and deployment wire 59 pays out in accordance with suction pile anchor penetration. The ROV continues monitoring the penetration rate, attitude (leveling), and pressure differential. See Fig. 9. Once full penetration is then achieved, the ROV closes the pump valve 28 and disengages from the suction pile anchor 10. Next, the ROV assists in the release of the ROV operable connector 64 from the lowering and lifting sling 66. The ROV moves the connector 64 to second load line connection 34 atop main mooring wire extension 32 and attaches it thereto. The connector 64 can be a keyhole-slot engagement secured with a keeper gate across the opening which can be manipulated by handles to shift the subsea connector. See Fig. 10. Once the connection of the deployment wire 59 to the second load line connection 34 is secure, the ROV 60 disengages wire grabber latch 36 on the upper portion of the suction pile anchor. See Fig. 11. The ROV then returns to the anchor handling vessel 40 at the surface, which vessel 40 then pays out deployment wire 59 to seafloor 16 (see Fig. 12) along a predetermined bearing while moving forward and pulling main mooring wire extension 32 taut through the mud. Referring to Fig. 13, a syntactic foam buoy block and sling assembly 70 suspended by deployment hook 72 is installed into the main mooring wire and the assembly is lowered with the deployment wire 59. Buoy assembly 70 suspends the end of the wire 59 above seafloor 16 where it remains accessible for recovery and deployment into a mooring array.

ROV 60 then disconnects deployment hook 72, and both the hook and the ROV are recovered to the vessel and the vessel proceeds to install the next suction pile anchor. This process is repeated until all suction pile anchors are set.

Fig. 14 illustrates the connection of mooring lines from a suction pile anchor to a drilling unit, here in the form of a semisubmersible drilling vessel, rig 78. The anchor handling vessel arrives loaded with wire and buoys to complete the mooring system for rig 78. The ROV is deployed to connect a lift wire to the predeployed main mooring wire section. Terminal buoy 70 may be provided with a transponder to facilitate location and hook-up. The lift wire is retrieved to anchor handling vessel 40 and an intermediate mooring wire 74 is connected to buoy 70. The intermediate wire is then deployed into the water and syntactic foam buoys 76 are connected to intermediate wire 74 and deployed overboard. An upper winch wire 82 is connected to buoys 76 and payed out while anchor handling vessel 40 returns to rig 78 to receive a rig wire 80 which is then connected to buoys 76. The buoys and rig wire are lowered with a j-lock chaser, allowing the rig to pre-tension the wire. Vessel 40 then returns to rig 78, lowering the winch wire 82, and allowing the j-lock chaser to disengage. The procedure is repeated for each additional anchor. As an alternative, the use of an ROV operable connector similar to connector 64 (Fig. 10) makes it possible to predeploy suction anchors with no mam mooring wires. See Fig. 16. This enables the anchor handling vessel 40 to deploy a suction pile 10, disconnect all lines with an ROV 60 and proceed with setting other suction pile anchors. Later the anchor handling vessel returns to install the mooring wire. This optional procedure is useful when a time constraints exist .

Referring to Fig. 17 anchor handling vessel 40 returns to location when drilling and/or production operations are over and it is time to move rig 78.

Vessel 40 lowers a recovery hook 86 on line 59, and ROV 60 is deployed to connect the recovery hook to a recovery sling 88 below buoy assembly 76. Rig 78 then slacks off rig mooring line 80, line 59 is taken in, and the anchor handling vessel heaves the buoy assembly 76 on deck using recovery sling 88. See Fig. 18. Rig wire 80 is disconnected from buoy assembly 76 and anchor handling vessel 40 returns the rig wire 80 to rig 78. See Fig. 19. Thereafter, recovery of intermediate mooring extension wire 74 proceeds with vessel 40 backing up and winching line 74 aboard over the stern roller. See Fig. 20.

It may be desirable to disconnect rig 78 and to retrieve intermediate mooring lines 74 in batch operations, doing this stage for each suction anchor pile ¹0 before returning to retrieve mooring wires 59 in a subsequent batch operation. In such batch operations, anchor handling vessel 40 returns mooring line 59 to the seafloor 16 with a syntactic buoy 70 in place with a recovery sling 90. See Fig. 21. Again, it may prove convenient to provide buoy 70 with a transponder to facilitate ROV location.

Primary mooring wire recovery operations begin with deployment of ROV 60 and a retrieval line 57 from anchor handling vessel 40. See Fig. 21. The ROV inserts hook 92 at the end of recovery wire into the eye of the recovery sling 90 attached to mam mooring wire 59. Backing up, the vessel uses its winch to retrieve first retrieval wire 57 and then primary mooring wire 59 over the stern roller until the vessel is over suction pile anchor 10 and mooring wire 59 is substantially vertical. See Fig. 22. The line is then aligned with the load line keeper 36 on suction pile anchor 10. Recall Fig. 11. Once wire 59 is guided into keeper 36, ROV 60 engages the lock of the keeper 36.

ROV 60 then disconnects subsea connector 64 from the second load connection 34 on mam mooring extension 32 and connects line 59 to lowering and lifting sling 66 presented by suction pile anchor 10. ROV 60 connects to pump port 28 and the pump system of the ROV injects water back into suction pile anchor 10. While water flows into the suction pile, the ROV directs the winch to begin lifting wire 59. Suction pile anchor 10 is raised in this manner until its bottom is within close proximity of the mud line. The ROV disengages from pump port 28 and opens flood valves 26. Recall Figs. 7-9. Retrieval resumes and suction pile anchor 10 is lifted to the surface staging position near the anchor handling vessel 40. The vessel lowers a tail-boardmg hook on line 58 and ROV 60 inserts it into the recovery sling. Recall Fig. 5. The weight of suction pile anchor 10 is accepted by line 58 which is connected to a winch line and ROV 60 is recovered. Vessel 40 proceeds slowly astern as the suction pile anchor is drawn to the roller to ensure proper skid alignment. The anchor handling vessel then progresses forward and water action on the anchor assists in orienting the anchor with the track roller as the winch heaves to board the suction pile anchor which is brought to rest in transport slot 42. Recall Figs. 4 and 3. The suction anchor vessel proceeds to the next anchor, repeating the recovery procedure.

Another type of batch operations may particularly facilitate developing a deepwater hydrocarbon reservoirs with drilling operations for a plurality of satellite subsea wells at adjacent sites. In this method a deepwater drilling rig with dynamic positioning capabilities is deployed. The deepwater drilling capabilities of the vessel is enhanced with a mooring system deployment beginning with setting a minimum array of suction pile anchors, e.g., four, and connecting mooring lines from the deepwater drilling rig prior to beginning drilling operations at a first site. Drilling is initiated relying, in part, on the vessel's dynamic positioning system while the anchor handling vessel returns for more suction pile anchors to complete the full complement of suction pile anchors. Returning, the vessel completes the mooring installing, e.g., another four for a total of eight suction pile anchor, and connecting mooring lines from the deepwater drilling rig during drilling operations at the first site.

The anchor handling vessel then returns for another load of suction pile anchors, setting a minimum array of suction pile anchors at a subsequent site while drilling operations are ongoing at the first site. Thereafter, when drilling is complete at the first site, drilling operations cease, the mooring lines are disengaged from the suction anchor piles, and the deepwater drilling rig moves to the subsequent site where it is connected to the minimum array of suction pile anchors already installed at that site. Additional suction pile anchors are retrieved from the first site and installed the subsequent site while drilling operations are ongoing. After the full complement of mooring lines are attached at the subsequent site, the remaining suction pile anchors are retrieved and installed for a minimum support at the next site, as the process repeats.

It will be seen that the present invention is particularly well adapted for use with mobile offshore drilling units such as SPAR structures that may be deployed for predrilling deepwater prospects or used for developing satellite sites. For such applications, rapid deployment, retrieval and redeployment is particularly beneficial and the repetitious nature of the application accentuates the economics of minimizing the equipment demands. However, other applications, including those combining long term production or combining drilling and production, may benefit from the present invention. An illustrative embodiment has been described using a single handling vessel. However, embodiments of the improved suction pile anchors and mooring systems can be deployed using two vessels, a second assisting to drag the suction pile anchor off the first and to assist with lowering.

Further, variations are intended with additional capacities and capabilities of anchor handling vessels. Various mooring configurations may also be deployed, with or without buoys, taut, catenary, or combined. Other modifications, changes, and substitutions are also intended in the foregoing disclosure. Further, in some instances, some features of the present invention will be employed without a corresponding use of other features described in these illustrative embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.

Claims

C L I M S

1. A suction pile anchor system for anchoring offshore structures to the seabed, the system including a suction pile having an upper end part provided with a pump valve for water to flow between the interior of the suction pile and the exterior thereof; and an ROV provided with pumping means connectable to the pump valve of the suction pile and operable so as to induce water to flow between the interior of the suction pile and the exterior thereof.

2. The system of claim 1, wherein said upper end part of the suction pile is provided with a flood valve for water to enter the suction pile, the flood valve being operable by the ROV.

3. The system of claim 1 or 2, further including a load support system which includes a first load connection arranged at the side of the suction pile, a load line connected to the first load connection, the load line being provided with a second load connection arranged at the end of the load line opposite the first load connection, and an installation connection provided at the top of the suction pile.

4. The system of claim 3, further comprising a selectively releasable load line keeper adjacent the top of suction pile for securing the load line to the suction pile during installation operations.

5. The system of claim 3 or 4, wherein said installation connection is provided with a releasable connector which is connectable to the second load line connection, said connector and said ROV being provided with co-operating means for releasing the connector from the installation connection and connecting the connector to the second load line connection.

6. The system of claim 5, wherein said connector is connected to a deployment wire extending from a vessel floating at the water surface, the deployment wire forming part of a mooring wire when the connector is connected to the second load line connection.

7. A method of installing the suction pile anchor system of claim 1, the method including connecting the pumping means of the ROV to the pump valve of the suction pile and operating the pumping means in one of a first mode in which water is evacuated from the suction pile so as to draw down the suction pile into the seabed, and a second mode in which a fluid is pumped into the suction pile so as to retrieve the suction pile.

8. The method of claim 7, wherein the pumping means is operated in the second mode, and wherein said fluid is selected from seawater and air.

9. A method of developing a deepwater hydrocarbon reservoir using the suction pile anchor system of claim 1, using a deepwater drilling rig with dynamic positioning capabilities, the method comprising: setting an array of suction pile anchors of said suction pile anchor system and connecting mooring lines from the deepwater drilling rig prior to beginning drilling operations at a first site; setting the remainder of the full complement of suction pile anchors and connecting mooring lines from the deepwater drilling rig during drilling operations at the first site; setting a minimum array of suction pile anchors of said suction pile anchor system at a second site while drilling operations are ongoing at the first site; ceasing drilling operations at the first site, disengaging the mooring lines from the suction anchor piles and moving the deepwater drilling rig to the second site; connecting mooring lines from the deepwater drilling rig to the minimum array of suction pile anchors at the second site; retrieving suction pile anchors from the first site and installing them at the second site during drilling operations at the second site.

10. The system substantially as described hereinbefore with reference to the accompanying drawings.

11. The method substantially as described hereinbefore with reference to the accompanying drawings.