First Permanent Polyester Prelay on the Seabed in

Gulf of Mexico

Todd Veselis

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

Contact Information

Todd Veselis InterMoor

Email: todd.veselis@intermoor.com Phone Number: 832-399-5018