The use of drag embedment anchors in offshore applications

Transcription

The use of drag embedment anchors
in offshore applications
by
Senol Ozmutlu
Vryhof Anchors BV – Netherlands
OTEO International Conference on Offshore Renewable Energy, 10-12 May
2012, Porto
Contents
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Introduction
Mooring systems
Offshore foundations: Anchors
Fluke anchors (Stevpris, Stevshark) and Plate anchors (Stevmanta VLA)
– Design
– Installation
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Real time tracking of anchor parameters (Stevtrack)
Selected project examples and reliability levels
Conclusions
The use of drag embedment anchors in offshore applications; by Senol Ozmutlu,
Offshore Renewable Energy, 10-12 May 2012, Porto
The vryhof scope:
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design, manufacturing and supply of High Holding Power (HHP) anchors and
tensioning equipment
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selection and supply of fit-to-purpose mooring line components and connectors
on behalf of clients
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operating an alliance of leading manufacturers of mooring line components
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Installation assistance
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Engineering services
Company milestones:
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1972
incorporation and Stevin anchor introduction
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1982
Stevpris anchor introduction
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1990
vryhof group diversification program
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1992
introduction of the mooring specialists alliance
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1996
Stevmanta VLA concept introduction
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1998
Stevmanta proven and operational offshore Brazil
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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
Many offshore units around the world are floating structures and are moored
OIL & GAS
RENEWABLE ENERGY & OFFSHORE CONSTRUCTION
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 2012 – 2014
• 1 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
Mooring systems in general : Catenary mooring
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chain
wire rope
drag embedment anchor
Mooring systems in general: Taut leg mooring
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synthetic rope
wire rope
vertical loaded anchor (VLA)
Mooring system elements
SEA LEVEL
90 m m rig w ire
Mooring systems are
•Either pre-installed
•or installed when the unit arrives at the location
Swivel
Shackle
Pearlink
Pearlink
Thim ble
133 m m x 1000 m
(or 1500 m )
polyester rope
Shackle
Sw ivel
Thim ble
Pearlink
Pearlink
84 m m x 500 m
O R Q chain
SEABED
15 m T Stevpris
M k5 Anchor
M OO RED O BJECT
Anchoring options
gravity anchor
Gravity installed: DPA, torpedo, etc
pile
suction pile
drag embedment anchor
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.
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
Stevpris Mk6
Stevshark Mk3, Mk5
Stevmanta VLA
Installation records: project distribution world-wide
Only a special category of drag embedment anchors is suitable for offshore use
A Class anchors
Anchor holding capacity in medium dense silica SAND
Typical Ultimate Holding Capacity [ton] -->
10000
1000
100
10
1
10
100
Anchor size [ton] -->
Stevpris Mk6
Bruce FFTS
Flipper Delta
Moorfast
Stockless
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
ANCHOR HOLDING CAPACITY & ANCHOR STABILITY
is a function of
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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.
Utilising results from anchor tests: Soft models
Empirical
Anchor _ UHC = Ac *W n
⎡ Fins ⎤
p
Anchor _ penetration = ⎢
⎥ * A pd * [W ]
⎢⎣UHC ⎥⎦
m
⎡ Fins ⎤
d
Anchor _ drag = ⎢
⎥ * Ad * [W ]
⎢⎣UHC ⎥⎦
CBR & KBR– 9000 anchors, thousands of documented installation
Numerical, constitutive
A simple anchor sizing exercise for generic soils
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soil
: very soft clay
: silica SAND
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forerunner
: chain
: chain
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required UHC
: 400 t
: 400 t
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pre-tension load
: 250 t
: 250 t
10 t
5t
Stevpris Mk6 size :
Fluke/shank angles
Small, middle and large fluke/shank angles.
Mounting and changing fluke-shank angle is simple and quick 25 – 40 min
shank
front pintle
fluke
sand angle
rear pintle
mud angle
Numerous Installation means and methods are applicable
See our anchor manual or visit www.vryhof.com
Stevpris® /Stevshark® handling/deployment with chaser
Stevpris® /Stevshark® can be retrieved by
•using mooring line itself
•PCP
•Recovery pennant
•Recovery bridle
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
Wire shank
Fluke plate
Streamlined fluke plate
Recovery socket
Characteristics of the Stevmanta VLA
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Deep penetrating anchor in soft soils
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Suitable for supporting large vertical and horizontal loads
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Optimal choice for semi-taut and taut leg moorings
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Easy installation: installed like a conventional drag embedment anchor
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After installation, loading at any angle (0 to 90 degrees)
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Loading in all directions possible
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V/H ratio : 2.5 to 3.5
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Easy anchor recovery
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)
Installation options: various methods are possible for details please refer to
Vryhof Anchor manual or www.vryhof.com/ammanual.htm
Option 1: Single line installation with one AHV
Single line installation: shear pin - angle adjuster
Stevmanta VLA recovery
1) With tail
2) With special sockets
3) pull-back the installation line:
double line and fixed angle
adjuster option
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
Load, anchor penetration and drag can be measured
At the field by simple means
As well as using advanced tools like Stevtrack
with the real time measurement of load at the anchor and anchor
positions/orientations
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 150 – 500 tons and at/above 820 tons
•Stevmanta VLA in congested areas
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
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
Mediterranean & AFRICA
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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
Brazil
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Stevpris and Stevshark are used for MODUs and permanent moorings
3 FPSO + 3 FPU moored with Stevmanta VLAs & Several MODUs with Stevmanta VLAs
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
Central America
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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
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
Canada - Alaska
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Stevpris – Stevshark on MODUs and
permanent units
Very dense or hard soils
Arctic conditions
60 mT (15mT) Stevshark Mk5 anchors
installed at 836 tons (5-15 m drag)
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

The use of drag embedment anchors in offshore applications

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