Objective
• History of polyester on the seabed • Discuss of why we took this approach for Mirage
– Advantages – Concerns?
• Review the polyester prelay approval process • Review the test plan and results
Project Overview • Field: Mirage (MC-941) /Telemark
(AT-63)
• Owner: ATP Oil and Gas Corporation
• Water Depth: 4,000 ft
• Hull Type: Deep Draft Floating Platform (DDFP) – MinDOC3
• Installation: 2009
History of Laying Polyester on Seabed
• Industry testing – late 1990’s – Came as a result of industries
work w/polyester – Various JIPs – Lab tests
• Inadvertent contact during – Installation – Service
• MODU moorings – Began in 2007 – Field trials – Industry experience
NTL 2009-G03
• Issued in Jan 2009 by BOEM/BSEE • Provides guidelines for permanent and MODU
moorings • Establishes conditions for presetting moorings on the
seabed including: – Use of ropes with proven filter barrier – Following recommendations in APR RP 2SM – Site survey – Rope inspection criteria
Advantages to Prelaying Polyester on Seabed
• Timing – Allows mooring to be set off critical path and at any time – Allows for changes in hull sail away/installation
• Installation – Eliminates need for handling surface/submersible
buoys – Eliminates risk of collision/loss of buoy – Allows all polyester to be handed during single
campaign
• Hookup – Eliminates the need to install polyester during hookup – Increased hookup efficiency – Increased flexibility
Approval Process
• Process was somewhat undefined because:
– First permanent mooring application where polyester was intentionally laid on seabed
• Goal was to: – Demonstrate, through
testing, that seabed contact would not have any adverse affects
Approval Process
• Satisfy requirements of NTL 2009-G03 • Submission of test plan to
BOEM/BSEE (formally MMS) for approval – Field test – Subrope testing – Lab testing
• Submission of test results to BOEM/BSEE
Field Test • Lowered two test sections
onto seabed using AHTS (Anchor Handling Tug Supply) vessel
• Performed two drag tests with inserts, each a minimum of 5 min with 5 min in between
• Left inserts on seabed for 24 hrs
• Recovered inserts to surface
Subrope Testing
• Modulus testing – 10th cycle (10% - 50%) – EA/MBL (Stiffness/Min. Break
Load)
• Break testing – Four control samples – (C) – Four insert samples – (I)
• Fatigue testing – 80,000 cycles – Load range – 15%-45% – Sample consisted of 3 full
scale subropes
Subrope Testing – Results
• Control and insert samples average break strength and modulus were within 1% of each other
• Sample survived 80,000 cycle fatigue test without issue
Subrope Testing – Results
Sample Breaking Strength
(kips) Modulus 10th Cycle 10-
50% (EA / MBL)
C.1 383.8 14.7
C.2 411.0 15.3
C.3 398.6 14.3
C.4 419.9 14.8
I.1 417.3 14.2
I.2 402.9 15.5
I.3 381.8 14.9
I.4 399.2 15.1 Mean Control Sub-ropes
(C.1-4) 403.3 14.8
Mean Insert Sub-ropes (I.1-4) 400.3 14.9
Lab Testing • Inspection performed on
both control and sample yarns
• Inspection included: – Visual Inspection – Fiber Testing – Yarn Analysis – Tenacity – Strength – SEM (Scanning Electron
Microscope) Photographs
Lab Testing Results
• No significant difference in:
– Break strength – Modulus – Wet yarn on yarn abrasion – Visual appearance
• Yarn from both samples looked new
• In very rare cases trace particles were found in outer core yarns
Conclusion • Testing demonstrated that:
– Soil filter was effective – Contact with the seafloor had no
adverse affects on the polyester
• For Mirage, prelaying on the seabed: – Saved time during hookup – Reduced risk