The use of drag embedment anchors in offshore applications

Transcription

1 The use of drag embedment anchors in offshore applications by Senol Ozmutlu Vryhof Anchors BV Netherlands OTEO International Conference on Offshore Renewable Energy, May 2012, Porto

2 Contents Introduction Mooring systems Offshore foundations: Anchors Fluke anchors (Stevpris, Stevshark) and Plate anchors (Stevmanta VLA) Design Installation Real time tracking of anchor parameters (Stevtrack) Selected project examples and reliability levels Conclusions

3 The vryhof scope: design, manufacturing and supply of High Holding Power (HHP) anchors and tensioning equipment selection and supply of fit-to-purpose mooring line components and connectors on behalf of clients operating an alliance of leading manufacturers of mooring line components Installation assistance Engineering services

4 Company milestones: 1972 incorporation and Stevin anchor introduction 1982 Stevpris anchor introduction 1990 vryhof group diversification program 1992 introduction of the mooring specialists alliance 1996 Stevmanta VLA concept introduction 1998 Stevmanta proven and operational offshore Brazil 2000 introduction of Deeprope Stevin, Stevpris, Stevshark, Stevmanta, Stevtensioner, Stevtrack. HQ and R&D is near Rotterdam with fabrication at Rotterdam Port Offices: Mooreast (Singapore) - Moorwest (Houston) - Vryhof do Brazil - Vryhof Russia

5 Many offshore units around the world are floating structures and are moored OIL & GAS

6 RENEWABLE ENERGY & OFFSHORE CONSTRUCTION

7 Projects in Renewable Energy Sector Completed projects Mooring of Wave Energy devices Offshore Scotland Mooring of Spar type Floating windmill HYWIND Offshore Norway Mooring of Semi-sub type Floating windmill WINDFLOAT Offshore Portugal Other small scale test units for wind, wave, tidal, and current devices Europe Projects currently running with installation targeted at Floating windmill offshore Spain 2 Floating windmills offshore southern France 2 Floating windmills offshore Japan 1 floating windmill USA Several wind, tidal, wave, and current devices planned in Europe, Africa, Asia, Japan

8 Mooring systems in general : Catenary mooring chain wire rope drag embedment anchor

9 Mooring systems in general: Taut leg mooring synthetic rope wire rope vertical loaded anchor (VLA)

10 Mooring system elements SEA LEVEL 90 mm rig wire MOORED OBJECT Mooring systems are Either pre-installed or installed when the unit arrives at the location Swivel Shackle Pearlink Thimble Pearlink 133 mm x 1000 m (or 1500 m) polyester rope Shackle Swivel Thimble Pearlink Pearlink 84 mm x 500 m ORQ chain SEABED 15 mt Stevpris Mk5 Anchor

11 Anchoring options gravity anchor pile suction pile Gravity installed: DPA, torpedo, etc drag embedment anchor

12 A drag embedment anchor is pulled in (dragged in) to the subseabed. The capacity and performance is a function of anchor type/size and the in-situ geotechical conditions.

13 Majority of the moored structures around the world uses drag anchors; Vryhof only over 9000 anchors - about 1600 anchors on permanent systems Stevin Stevpris Mk3, Mk5 Stevshark Mk3, Mk5 Stevpris Mk6 Stevmanta VLA

14 Installation records: project distribution world-wide

15 Only a special category of drag embedment anchors is suitable for offshore use A Class anchors

16 Anchor holding capacity in medium dense silica SAND Typical Ultimate Holding Capacity [ton] --> Anchor size [ton] --> Stevpris Mk6 Bruce FFTS Flipper Delta Moorfast Stockless

17 DESIGN PROCESS : requirements / specs Client specifies Mooring / metocean conditions Type of mooring system Spread or single point Catenary or taut or semi-taut Type of moored object Permanent (FPSO, FSO, FPI) Temporary (MODU, barge, etc) Mooring line characteristics Anchor loads (quasi-static / dynamic) intact damaged transient Specifications and applicable codes Client may provide Site conditions Location (maps) Bathymetry Geophysical data Geohazards Geological data Geotechnical data Suitable anchor type & size fluke/shank angle setting Drag + Penetration Inverse catenary of forerunner Installation requirements Installation performance Long term performance Client requires

18 ANCHOR HOLDING CAPACITY & ANCHOR STABILITY is a function of soil conditions, anchor type, anchor size Fluke/shank angle setting ANCHOR CAPACITY & STABILITY is not dependent on the dead weight / dry weight of the anchor but on the design / geometry of the anchor!! Our designs meets the requirements of the all classifications societies or regulatory authorities. We have working experience will all classification societies worldwide.

19 Utilising results from anchor tests: Soft models Empirical Anchor _ UHC = A c * W n F ins UHC Anchor _ penetration = m F Anchor _ drag ins = * UHC A d * A pd *[ W ] d p *[ W ] CBR & KBR 9000 anchors, thousands of documented installation Numerical, constitutive

20 A simple anchor sizing exercise for generic soils soil : very soft clay : silica SAND forerunner : chain : chain required UHC : 400 t : 400 t pre-tension load : 250 t : 250 t Stevpris Mk6 size : 10 t 5 t

21 Fluke/shank angles Small, middle and large fluke/shank angles.

22 Mounting and changing fluke-shank angle is simple and quick min shank front pintle fluke rear pintle sand angle mud angle

23 Numerous Installation means and methods are applicable See our anchor manual or visit Stevpris /Stevshark handling/deployment with chaser

24 Stevpris /Stevshark can be retrieved by using mooring line itself PCP Recovery pennant Recovery bridle

25 STEVMANTA VLA: anchor of choice for semi-taut and taut leg moorings with very high vertical and horizontal loads Permanent moorings Temporary moorings, MODUs Angle adjuster Angle adjuster Shear pin Chain shank Fluke plate Wire shank Streamlined fluke plate Recovery socket

26 Characteristics of the Stevmanta VLA Deep penetrating anchor in soft soils Suitable for supporting large vertical and horizontal loads Optimal choice for semi-taut and taut leg moorings Easy installation: installed like a conventional drag embedment anchor After installation, loading at any angle (0 to 90 degrees) Loading in all directions possible V/H ratio : 2.5 to 3.5 Easy anchor recovery

27 Stevmanta VLA is suitable for high mooring loads with 0 to 90 uplift angle at the mudline AND loading directions with 360 degrees freedom (weathervaning systems)

28 Installation options: various methods are possible for details please refer to Vryhof Anchor manual or Option 1: Single line installation with one AHV Single line installation: shear pin - angle adjuster

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30 Stevmanta VLA recovery 1) With tail 2) With special sockets 3) pull-back the installation line: double line and fixed angle adjuster option

31 Other installation options for drag embedment anchors are to use surface or subsea tensioning methods High horizontal loads with vertical pull in the order of 40% to 50% of the required tension Use of small installation vessels Real-time measurement and record of tension data Less sensitive to sea state

32 Load, anchor penetration and drag can be measured At the field by simple means

33 As well as using advanced tools like Stevtrack with the real time measurement of load at the anchor and anchor positions/orientations

34 Stevpris, Stevshark, and Stevmanta anchors have a long successful track record EUROPE NORTH SEA Both permanent and temporary/mobile units Stevpris/Stevshark common Anchors installed and proof tension tested tons and at/above 820 tons Stevmanta VLA in congested areas

35 Stevpris, Stevshark, and Stevmanta anchors have a long successful track record Middle East Arabian gulf Permanent and temporary moorings with Stevpris / Stevshark Mk5 anchors 11 to 31 tons installed at 200 to 600 tons in cemented carbonate soils

36 Stevpris, Stevshark, and Stevmanta anchors have a long successful track record South East Asia - Australia Over 200 permanent projects where Vryhof anchors are being used Many FPSOs, FSOs, SPMs, CALM buoys etc. anchored with Stevpris & Stevshark anchors Many MODUs operating in the region are using Stevpris & Stevshark anchors Stevmanta VLAs used: MODU moorings and marine/civil construction Stevshark Mk5 is the anchor for Australian carbonate settings: cemented soils, calcarenite, calcilutite, etc. 25 mt Stevpris anchors installed and proof tension tested above 725 tons Stevtensioner: commonly used

37 Stevpris, Stevshark, and Stevmanta anchors have a long successful track record Mediterranean & AFRICA Stevpris and Stevshark anchors installed in record times MODU, SPM, FSO and FPSO moorings MODUs moored with Stevmanta VLAs at water depths of ~2000 m Single point / weatherwaning moorings with Stevmanta VLAs over 1300 m water depth Anchors installed and proof tension tested above 760 tons

38 Stevpris, Stevshark, and Stevmanta anchors have a long successful track record Brazil Stevpris and Stevshark are used for MODUs and permanent moorings 3 FPSO + 3 FPU moored with Stevmanta VLAs& Several MODUswith StevmantaVLAs Water depths where Stevmanta VLAs used have reached over 2150 meters Design UPC level has reached over 1200 tons Polyester common 2 to 4 anchor legs are completed per day

39 Stevpris, Stevshark, and Stevmanta anchors have a long successful track record Central America Stevpris and Stevshark on MODU and permanent mooring systems 36 mt Stevpris Mk5 anchors in extremely soft organic soil Anchors proof tension tested at 688 tons

40 Stevpris, Stevshark, and Stevmanta anchors have a long successful track record GOM Stevpris / Stevshark is common Several MODUs using Stevmanta VLAs Water depths over 1600 meters Polyester and wire rope systems Smaller AHVs, yet 3 to 4 anchor legs per day

41 Stevpris, Stevshark, and Stevmanta anchors have a long successful track record Canada - Alaska Stevpris Stevsharkon MODUsand permanent units Very dense or hard soils Arctic conditions 60 mt (15mT) Stevshark Mk5 anchors installed at 836 tons (5-15 m drag)

42 CONCLUSIONS Drag Embedment Anchors (DEA) are simple but robust offshore foundations Design is based on soil mechanics principles Requires less soil data (i.e. huge cost savings in site investigation campaigns) Well tested and proven technology Large track record worldwide; Vryhof only over 9000 anchors Anchor capacity, penetration, drag, and long term behavior are well predicted DEAs are field load tested; reliability level is verified before put in service Simple installation methods: the installation does not require special vessels DEAs are recoverable and re-usable DEAs are cheaper than other offshore foundations; less offshore installation budget