SDV to Deploy SST
(14th April 2016)
Subsea Deployment Systems Ltd.
Subsea Deployment Systems Ltd.
INTRODUCTION
• An installation method that overcomes the needs for a heavy lift vessel
• Low risk / low tech / low cost installation method
• Reduced weather sensitivity
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Subsea Deployment Systems Ltd.
SUBSEA DEPLOYMENT VESSEL (SDV) & SST
Control chain
Buoyancy modules
Tow chain clump weight
Control tower
Castle
Interface frame
c/w ballast locker
Floodable hull
Subsea Storage Tank (SST)
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Subsea Deployment Systems Ltd.
INSTALLATION SCENARIOS
Base Case
• SST filled with fresh water giving a net weight of 1500t
Optional Case
• SST filled with oil giving a net weight of 200t
In both cases the installation method will be similar but a smaller SDV would be used
for the optional case.
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Subsea Deployment Systems Ltd.
SDV MAIN PARTICULARS
• Length
35.2m
• Width
29.2m
• Depth
5.0m
• Overall height
13.0m
(Est. 21.5m incl. interface frame)
• 408 no. 3x3x1m buoyancy modules
• Steel
• Scrap chain
525t
1800t
• Displacement 3400t
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Subsea Deployment Systems Ltd.
OUTLINE INSTALLATION METHOD
Load out
• Dock on interface frame
• Flood and lower the SST
below the surface
• Float SDV over and
connect to SST
• Flood and lower the
SST until fully supported
by the SDV
• Disconnect inshore HLV
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Subsea Deployment Systems Ltd.
OUTLINE INSTALLATION METHOD
Tow
• Shallow water tow
• Flood of all tanks and piping
• Surface tow with nominal buoyancy
• Deploy tow chain and fully submerge the assembly
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Subsea Deployment Systems Ltd.
OUTLINE INSTALLATION METHOD
Approach
• Adjust tow wire
and tow speed
to slow down
upon approach
to site
• Lower tow chain
clump weight on
to temporary
target with SST
in range of final
target
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Subsea Deployment Systems Ltd.
OUTLINE INSTALLATION METHOD
Landing
• Lower control chains into control towers
• Pay-out until the system is neutral and lower the assembly on to target
• When landed lower control chains into control towers and temporarily disconnect
• Install ballast equivalent to SST weight
• Disconnect SST from interface frame
• Reconnect to control chains
• Raise SDV clear of SST by raising
control chains
• Pull control chains clear of SDV
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Subsea Deployment Systems Ltd.
OUTLINE RECOVERY METHOD
Recover SDV
• Tow chain clump weight anchors the SDV
• Recover wire to bring the chain clear of the seabed and slowly move forward
• Increase tow speed and adjust tow wire until SDV at suitable depth
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Subsea Deployment Systems Ltd.
CONTROL CHAIN TOWERS - DYNAMICS
Control chain / towers
• Vertical control
• Lateral control
• Rotational control
• On-bottom weight
Dynamics
• Natural period > 120s
• Response amplitude < 20%
of surface vessel
• Soft-soft landing
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Subsea Deployment Systems Ltd.
SAFETY AND ENVIRONMENT
Considering like for like operation
• Small number of people directly involved in operation (typ. 1:10)
• Environmental impact considerably less
+
VS
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Subsea Deployment Systems Ltd.
INHERENT SAFETY
General
• Total loss minimised –
“close to neutral”
• Insensitive to weather
• No point of ‘no return’
Rigging failure
• No catastrophic loss
Tow wire failure (10x)
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Subsea Deployment Systems Ltd.
VESSELS
• Currently 10 AHTs on the spot market with WROV fitted
• Some with offshore crane (crane not strictly required)
• All with DP II capability and BP > 220t
• Other 30+ AHTs on the North Sea spot market
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Subsea Deployment Systems Ltd.
SEASTATE STATISTICS
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Subsea Deployment Systems Ltd.
SUMMARY
• Largely failsafe and very low tech
• Larger weather window (wave & ice)
• Potentially greater availability compared to HLVs
• Potential for phased installation when not relying on HLV
• Technology is considered “disruptive” by major contractors
• SDS is looking for an opportunity to develop the concept into a working solution
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