OA11409A

OA11409A - Rov installed suction piles.

Info

Publication number: OA11409A
Application number: OA1200000130A
Authority: OA
Inventors: William Henry Von Eberstein
Original assignee: Shell Int Research
Priority date: 1997-11-01
Filing date: 2000-04-28
Publication date: 2004-04-20
Also published as: ID23926A; NO20002236L; GB0010174D0; GB2350341B; WO1999022983A1; GB2350341A; NO334253B1; BR9813332A; NO20002236D0

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

1 011409

ROV INSTALLED SUCTION PILES

The présent invention relates to a suction pile anchorSystem for securing offshore structures to the seabed.

Such structures include for example floating offshoredrilling and/or production vessels which must bemaintained in position over a well site for offshoredrilling operations and often for production operations.This often requires the deployment of an array of mooringUnes, each anchored to the seabed with a pile foundationor the like. Installing such foundation éléments forsecure anchorage is time consuming and requiresconsidérable offshore equipment.

Another problem arising in deepwater is that thespread of these mooring Unes can be substantial andanchor structures are widely placed over a leasehold oreven into adjacent lease blocks and the mooring arrays ofadjacent blocks can overlap. Further, the sequential stepsin development of such well site requires explorationwells, test wells, satellite subsea wells, etc., each ofwhich can leave foundation éléments in the seafloor sothat the seafloor actually becomes crowded in relation tothe necessary infrastructure for working offshoreprospects.

Suction pile anchors as disclosed in U.S. PatentNo. 4,318,641 hâve been known as an alternative to drivingor drilling and grouting piles. These anchors provideopportunity for easier installation, but the installationof suction pile anchors in deepwater remains equipmentintensive and does not facilitate foundation removal.

Thus, there remains a need for a method and System foranchoring offshore structures and vessels which 2 011409 facilitâtes ease of deployment with a minimum ofequipment.

In accordance with the invention tnere is provided asuction pile anchor System for anchoring offshore 5 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 ofthe suction pile and the exterior thereof; and an ROV provided with pumping means connectable to the10 pump valve of the suction pile and opérable so as to induce water to flow between the interior of the suctionpile and the exterior thereof.

By attaching the ROV to the suction pile to evacuatewater from the suction pile, the pile can be installed in 15 deepwater applications without requiring complicated equipment such as guidance wires for lowering a pumpfacility from a surface vessel to the suction pile.Furthermore, the suction pile can be adequately retrievedto surface by attaching the ROV to the suction pile and 20 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 isfurther provided with a flood valve for water to enterthe suction pile, the flood valve being opérable by the 25 ROV.

The suction pile is lowered into the water with theflood valve open. After the pile has reached the seabedand has partly penetrated the seabed under its ownw.eight, the ROV closes the flood valve and attaches to 30 the pump valve to evacuate water from the pile.

The invention will be described further in moredetail and by way of example with reference to theaccompanying drawings in which: 3 011409

Fig. 1 schematically shows a floating vessel anchoredin accordance with the System of the invention;

Figs. 2 and 2A schematically show a suction pileanchor installed in the océan floor in accordance with 5 the invention; and

Figs. 3-22 schematically show various steps in thedeployment of a suction pile anchor System in accordancewith the invention.

Fig. 1 illustrâtes one application of the présent10 invention. Here the suction pile anchors 10 secure a truss .spar configuration mobile offshore drilling unit("MODU") 12 in position over well site 14 at océanfloor 16. Each suction pile anchor is securely set withinthe océan floor and is connected to MODU 12 through 15 mooring or load Unes 18. The use of faut line moorings may reduce the mooring spread. Further, buoys 20 may beincluded into the mooring Unes.

Fig. 2 illustrâtes a suction pile anchor 10 installedin océan floor 16. The suction pile anchor has a suction 20 pile 22, here in the form of a cylinder having an open lower end and a closed upper end. A first loadconnection 24, here provided by load pad-eyes 24A, isprovided on the side of the suction pile, positioned to beaway from the ends of the suction pile and well below the 25 mud line on deployment. Under load conditions with this configuration, the load will be resisted most efficientlyby the océan floor 16.

Flooding ports or valves 26 and pump or pressure portor valve 28 are provided through or adjacent the closed 30 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 atthe top of the suction pile. Here the installationconnection includes a lowering and lifting sling 66. 4 011409 A load line or main mooring wire extension 32 isconnected to the first load connection 24 and provides anROV opérable second load line connection 34 above mudline16A of océan floor 16. In Fig. 2, main mooring wire 5 extension 32 holds second load line connection 34 in an accessible position through the inhérent stiffness of thewire rope over short distances and a load line keeper orwire grabber latch 36.

Fig. 2A illustrâtes an alternative embodiment in which10 the accessibility of second load line connection 34 above _the mudline is secured with a buoy 38 attached to the mainmooring wire extension.

Fig. 3 illustrâtes the work deck of an anchorhandling vessel 40 equipped to deliver and deploy four 15 suction pile anchors 10 per excursion. The suction pile anchors are locked into cradles or transport slots 42 inwhich horizontal skids 44 provide stability for controlled deployment of the suction pile anchors. Wire46 is spooled onto winches 41 provided on the deck of 20 anchor handling vessel 40.

Fully loaded, the vessel travels to the installation site and the first suction pile anchor 10 is positionedfor deployment. Preferably, this is with a two-way,hydraulically powered track roller assembly 43 which 25 facilitâtes rapid, smooth suction pile positioning.

Referring to Fig. 4, the suction pile anchor smoothlyrolls from the vessel, over stern roller 48, and into thewater with flooding valves 26 open. At this stage, anoverboard-ing wire 58 supports the weight of suction 30 anchor pile 10. After the anchor clears the stern roller, its weight is accepted by a deployment wire 59 connectedto lowering and lifting sling 66 by an ROV opérableconnector 64, see Fig. 5. Descent of the suction pileanchor pauses at a shallow staging station below anchor 5 011409 handling vessel 40 and an ROV 60 is launched from thevessel to disconnect the overboarding hook from thesling.

Descent résumés and ROV 60 follows as suction pile5 anchor 10 is lowered to a bottom staging station point very near seafloor 16. The suction pile anchor has atendency to rotate during descent and the ROV may need toproperly orient suction pile anchor 10 such that firstload connection 24 is aligned with the intended mooring 10 _ line orientation. See Fig. 6. The suction pile anchor is “then lowered for self-penetration under its own weightinto the upper silt line of seafloor 16 and into claymuck. In this interval, the pay out of deployment were 59is monitored so that it does not exceed the rate of self 15 pénétration.

At this point ROV 60 attaches itself to the top ofsuction pile anchor 10 and closes flooding valves 26. SeeFig.. 7. Continuing with Fig. 8, the ROV then engages pumpvalve 28 and pumps arranged within the ROV begin 20 evacuating water from suction pile 10 and deployment wire

59 pays out in accordance with suction pile anchorpénétration. The ROV continues monitoring the pénétrationrate, attitude (leveling), and pressure differential. SeeFig. 9. Once full pénétration is then achieved, the ROV 25 closes the pump valve 28 and disengages from the suction pile anchor 10. Next, the ROV assists in the release ofthe ROV opérable connector 64 from the lowering andlifting sling 66. The ROV moves the connector 64 tosecond load line connection 34 atop main mooring wire 30 extension 32 and attaches it thereto. The connector 64 can be a keyhole-slot engagement secured with a keepergâte across the opening which can be manipulated byhandles to shift the subsea connector. See Fig. 10. ο 011409

Once the connection of the deployment wire 59 to thesecond load line connection 34 is secure, the ROV 60disengages wire grabber latch 36 on the upper portion ofthe suction pile anchor. See Fig. 11. The ROV thenreturns to the anchor handling vessel 40 at the surface,which vessel 40 then pays out deployment wire 59 toseafloor 16 (see Fig. 12) along a predetermined bearingwhile moving forward and pulling main mooring wireextension 32 taut through the mud. Referring to Fig. 13,a syntactic foam buoy block and sling assembly 70suspended by deployment hook 72 is installed into themain mooring wire and the assembly is lowered with thedeployment wire 59. Buoy assembly 70 suspends the end ofthe wire 59 above seafloor 16 where it remains accessiblefor recovery and deployment into a mooring array. ROV 60 then disconnects deployment hook 72, and boththe hook and the ROV are recovered to the vessel and thevessel proceeds to install the next suction pile anchor.This process is repeated until ail suction pile anchorsare set.

Fig. 14 illustrâtes the connection of mooring Unesfrom a suction pile anchor to a drilling unit, here inthe form of a semisubmersible drilling vessel, rig 78.

The anchor handling vessel arrives loaded with wire andbuoys to complété the mooring System for rig 78. The ROVis deployed to connect a lift wire to the predeployedmain mooring wire section. Terminal buoy 70 may beprovided with a transponder to facilitate location andhook-up. The lift wire is retrieved to anchor handlingvessel 40 and an intermediate mooring wire 74 isconnected to buoy 70. The intermediate wire is thendeployed into the water and syntactic foam buoys 76 areconnected to intermediate wire 74 and deployed overboard.An upper winch wire 82 is connected to buoys 76 and payed 7 011409 out while anchor handling vessel 40 returns to rig 78 toreceive a rig wire 80 which is then connectée! to buoys76. The buoys and rig wire are lowered with a j-lockchaser, allowing the rig to pre-tension the wire. Vessel 5 40 then returns to rig 78, lowering the winch wire 82, and allowing the j-lock chaser to disengage. Theprocedure is repeated for each additional anchor.

As an alternative, the use of an ROV opérableconnector similar to connector 64 (Fig. 10) makes it 10 possible to predeploy suction anchors with no main "mooring wires. See Fig. 16. This enables the anchorhandling vessel 40 to deploy a suction pile 10-,disconnect ail- Unes with an ROV 60 and proceed withsetting other suction pile anchors. Later the anchor 15 handling vessel returns to install the mooring wire. This optional procedure is useful when a time constraintsexist.

Referring to Fig. 17 anchor handling vessel 40returns to location when drilling and/or production 20 operations are over and it is time to move rig 78.

Vessel 40 lowers a recovery hook 86 on line 59, and ROV60 is deployed to connect the recovery hook to a recoverysling 88 below buoy assembly 76. Rig 78 then slacks offrig mooring line 80, line 59 is taken in, and the anchor 25 handling vessel heaves the buoy assembly 76 on deck using recovery sling 88. See Fig. 18. Rig wire 80 isdisconnected from buoy assembly 76 and anchor handlingvessel 40 returns the rig wire 80 to rig 78. See Fig. 19.Thereafter, recovery of intermediate mooring extension 30 wire 74 proceeds with vessel 40 backing up and winching line 74 aboard over the stern roller. See Fig. 20.

It may be désirable to disconnect rig 78 and toretrieve intermediate mooring Unes 74 in batchoperations, doing this stage for each suction anchor pile 8 011409 10 before returning to retrieve mooring wires 59 in asubséquent batch operation. In such batch operations,anchor handling vessel 40 returns mooring line 59 to theseafloor 16 with a syntactic buoy 70 in place with a 5 recovery sling 90. See Fig. 21. Again, it may prove convenient to provide buoy 70 with a transponder tofacilitate ROV location.

Primary mooring wire recovery operations begin withdeployment of ROV 60 and a retrieval line 57 from anchor 10 handling vessel 40. See Fig. 21. The ROV inserts hook 92 at the end of recovery wire into the eye of the recoverysling 90 attached to main mooring wire 59. Backing up,the vessel uses its winch to retrieve first retrievalwire 57 and then primary mooring wire 59 over the stern 15 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 36on suction pile anchor 10. Recall Fig. 11. Once wire 59is guided into keeper 36, ROV 60 engages the lock of the 20 keeper 36. ROV 60 then disconnects subsea connector 64 from thesecond load connection 34 on main mooring extension 32and connects line 59 to lowering and lifting sling 66presented by suction pile anchor 10. ROV 60 connects to 25 pump port 28 and the pump System of the ROV injects water back into suction pile anchor 10. While water flows intothe suction pile, the ROV directs the winch to beginlifting wire 59. Suction pile anchor 10 is raised in thism.anner until its bottom is within close proximity of the 30 mud line. The ROV disengages from pump port 28 and opens flood valves 26. Recall Figs. 7-9. Retrieval résumés andsuction pile anchor 10 is lifted to the surface stagingposition near the anchor handling vessel 40. The vessellowers a tail-boarding hook on line 58 and ROV 60 inserts 9 011409 it into the recovery sling. Recall Fig. 5. The weight ofsuction pile anchor 10 is accepted by line 58 which isconnected to a winch line and ROV 60 is recovered.

Vessel 40 proceeds slowly astern as the suction pile 5 anchor is drawn to the roller to ensure proper skid alignment. The anchor handling vessel then progressesforward and water action on the anchor assists inorienting the anchor with the track roller as the winchheaves to board the suction pile anchor which is brought 10 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 réservoirs15 with drilling operations for a plurality of satellite subsea wells at adjacent sites. In this method a deepwaterdrilling rig with dynamic positioning capabilities isdeployed. The deepwater drilling capabilities of thevessel is enhanced with a mooring System deployment 20 beginning with setting a minimum array of suction pile anchors, e.g., four, and connecting mooring Unes from thedeepwater drilling rig prior to beginning drillingoperations at a first site. Drilling is initiated relying,in part, on the vessel's dynamic positioning System while 25 the anchor handling vessel returns for more suction pile anchors to complété the full complément of suction pileanchors. Returning, the vessel complétés the mooringinstalling, e.g., another four for a total of eightsuction pile anchor, and connecting mooring Unes from the 30 deepwater drilling rig during drilling operations at the first site.

The anchor handling vessel then returns for anotherload of suction pile anchors, setting a minimum array ofsuction pile anchors at a subséquent site while drilling 10 011409 operations are ongoing at the first site. Thereafter, whendrilling is complété at the first site, drillingoperations cease, the mooring Unes are disengaged fromthe suction anchor piles, and the deepwater drilling rigmoves to the subséquent site where it is connected to theminimum array of suction pile anchors already installed atthat site. Additional suction pile anchors are retrievedfrom the first site and installed the subséquent sitewhile drilling operations are ongoing. After the fullcomplément of mooring Unes are attached at the subséquent-site, the remaining suction pile anchors are retrieved andinstalled for a minimum support at the next site, as theprocess repeats.

It will be seen that the présent invention isparticularly well adapted for use with mobile offshoredrilling units such as SPAR structures that may bedeployed for predrilling deepwater prospects or used fordeveloping satellite sites. For such applications, rapiddeployment, retrieval and redeployment is particularlybénéficiai and the repetitious nature of the applicationaccentuâtes the économies of minimizing the equipmentdemands. However, other applications, including thosecombining long term production or combining drilling andproduction, may benefit from the présent invention.

An illustrative embodiment has been described using asingle handling vessel. However, embodiments of theimproved suction pile anchors and mooring Systems can bedeployed using two vessels, a second assisting to dragthe suction pile anchor off the first and to assist withlowering.

Further, variations are intended with additionalcapacities and capabilities of anchor handling vessels.Various mooring configurations may also be deployed, withor without buoys, taut, catenary, or combined. 11 011409

Other modifications, changes, and substitutions arealso intended in the foregoing disclosure. Further, insome instances, some features of the présent inventionwill be employed without a corresponding use of other 5 features described in these illustrative embodiments.

Accordingly, it is appropriate that the appended daimsbe construed broadly and in a manner consistent with thescope of the invention.

Claims

12 011409 NEW CLAIMS

1. A suction pile anchor System for anchoring offshorestructures to the seabed, the System including a suction pile (10) having an upper end part providedwith a pump valve (28) for water to flow between theinterior of the suction pile (10) and the exteriorthereof; and an ROV (60) provided with pumping means connectableto the pump valve (28) of the suction pile (10) andopérable so as to induce water to flow between theinterior of the suction pile (10) and the exteriorthereof.

2. The System of claim 1, wherein said upper end part ofthe suction pile is provided with a flood valve (26) forwater to enter the suction pile (10), the flood valve (26) being opérable by the ROV (60).

3. The System of claim 1 or 2, further including a loadsupport System which includes a first loadconnection (24) arranged at the side of the suctionpile (10), a load line (32) connected to the first loadconnection (24), the load line (32) being provided with asecond load connection (34) arranged at the end of theload line (32) opposite the first load connection, and aninstallation connection (66) provided at the top of thesuction pile.

4. The System of claim 3, further comprising a selectively releasable load line keeper (36) adjacent thetop of suction pile for securing the load line (32) tothe suction pile (10) during installation operations.

5. The System of claim 3 or 4, wherein said installationconnection (66) is provided with a releasableconnector (64) which is connectable to the second load 13 011409 line connection (34), said connector (64) and saidROV (60) being provided with co-operating means forreleasing the connector (64) from the installationconnection (66) and connecting the connector (64) to the 5 second load line connection (34).

6. The System of claim 5, wherein said connector (64) isconnected to a deployment wire (59) extending from avessel (40) floating at the water surface, the deploymentwire (59) forming part of a mooring wire when the 10 connector (64) is connected to the second load line -connection (34). Ί . A method of installing the suction pile anchor Systemof claim 1, the method including connecting the pumpingmeans of the ROV (60) to the pump valve (28) of the 15 suction pile (10) and operating the pumping means in one of a first mode in which water is evacuated from thesuction pile (10) so as to draw down the suctionpile (10) into the seabed, and a second mode in which afluid is pumped into the suction pile (10) so as to 20 retrieve the suction pile.

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

9. A method of developing a deepwater hydrocarbon 25 réservoir using the suction pile anchor System of claim 1, using a deepwater drilling rig (78) with dynamicpositioning capabilities, the method comprising: setting an array of suction pile anchors (10) of saidsuction pile anchor System and connecting mooring 30 Unes (80) from the deepwater drilling rig prior to beginning drilling operations at a first site; setting the remainder of the full complément ofsuction pile anchors (10) and connecting mooringUnes (80) from the deepwater drilling rig during 35 drilling operations at the first site; 14 10 011409 setting a minimum array of suction pile anchors (10)of said suction pile anchor System at a second site whiledrilling operations are ongoing at the first site; ceasing drilling operations at the first site,disengaging the mooring Unes (80) from the suctionanchor piles (10) and moving the deepwater drillingrig (78) to the second site; connecting mooring Unes (80) from the deepwaterdrilling rig (78) to the minimum array of suction pileanchors (10) at the second site; retrieving suction pile anchors (10) from the firstsite and installing them at the second site duringdrilling operations at the second site.