SAFE OFFSHORE VESSEL POSITIONING PRACTICE MOORING ANALYSIS ORCAFLEX

SAFE OFFSHORE VESSEL POSITIONING PRACTICE MOORING ANALYSIS ORCAFLEX WORKSHOP, 23 RD JUN 2012 IDEC, INTERCONTINENTAL, MUMBAI Veda m Design & Technology Center VEDAM DESIGN & TECHNICAL CONSULTANCY PVT. LTD. 504 -506, Acropolis, Military Road, Marol, Andheri (E), Mumbai-59, INDIA +91 -22 -67109192 , +91 -22 - 67257237 vedam@vedamindia. com, www. vedamindia. com

AGENDA Challenges in present Station Keeping Mooring Analysis … A glance Mooring Analysis – Usage Mooring Analysis – Stages, Categories Advantage with FUGRO-Vedam collaboration Vedam Design & Technology Center

Vedam CHALLENGES IN PRESENT STATION KEEPING Design & Technology Center Ø Complex platform and sub-sea infrastructure Ø Vessel positioning in close proximity to assets Ø Stringent safety requirement Ø Longer mooring durations Ø Operational requirement: gangway connections, helicopter operations Ø Vessel response under accidental damage of a line Ø Support vessel’s movement in close proximity to barge Ø Unconventional requirements: Connection to Jacket leg, DP buoys etc. . MOORING ANALYSIS IS A TOOL TO SIMULATE COMPLEX NATURE OF STATION KEEPING TO ENSURE SAFETY AND REDUCE RISK DURING OFFSHORE OPERATION

Global Standards… Vedam Design & Technology Center

Vedam Design & Technology Center POSITIONING SERVICE – WAY AHEAD… CLIENT/MWS Field Survey Anchor Pattern Mooring Analysis

Vedam Design & Technology Center MOORING ANALYSIS – AN OVERVIEW. . . OUTPUT MOORING ANALYSIS INPUT • Anchor Pattern • Environment • Location • RAO CALCUATION • MOORING ANALYSIS • CODE CHECK • LINE TENSIONS • LIMITNG ENVIRONMENT • DP BUOYS

Vedam Design & Technology Center MOORING ANALYSIS – AN OVERVIEW. . . Ø Motion analysis & determining RAO Ø Modelling of mooring pattern Ø Quasi-static Mooring Analysis (equilibrium position) Ø Rule Check as per API/ISO/DNV Standards

MOORING ANALYSIS … AN OVERVIEW Ø Catenary shape & positioning of mooring buoy o Safe vertical distance from sub-sea pipelines o Limiting anchor loads o Chain lengths for DP buoys Ø One line Damage analysis o Limiting line tensions o Limiting vessel excursions Vedam Design & Technology Center

MOORING ANALYSIS … AN OVERVIEW Ø Transient analysis o Vessel trajectory after breakage of a line o Maximum vessel offsets from platform/assets. Ø Detailed Report and Anchor Pattern with catenary diagrams, Vedam Design & Technology Center

USAGE OF MOORING ANALYSIS … Vedam Design & Technology Center Ø Derivation of exact catenary shapes Ø Correct estimation of distance between subsea structure and mooring lines/anchors. Ø Mooring optimization to meet stringent safety requirement Ø Stabilisation of vessel motion, excursion Ø Clash Check Ø Usage of Damage Prevention Buoys Ø Derivation of limiting weather Ø Vessel Relocation Capability

MOORING ANALYSIS… CATENARY SHAPE Ø Deployed wire length Ø Initial tension in the wire Ø Load on Anchor Ø Location and size of DP buoys Ø Load on vessel’s mooring fittings Ø Safe navigation zone around moored vessel Vedam Design & Technology Center

Vedam MOORING ANALYSIS… COMPLEX FIELD LAYOUT Design & Technology Center ØLimiting Vessel excursion ØDistance from pipe lines ØDistance from floating bodies ØUneven distribution of spread mooring ØSupport from Jacket Leg

Vedam Design & Technology Center MOORING ANALYSIS… STRINGENT SAFETY CRITERIA Ø Effect of different directional weather Ø Effect of extreme weather condition Ø Effect of one line damage condition Ø Limitation to excursion Ø Factor of Safety of anchor, line & mooring fittings

Vedam Design & Technology Center MOORING ANALYSIS… VESSEL STABILISATION ØLimiting vessel roll & pitch motion ØLimiting vessel’s heave motion for § Better habitability § Safe operation of gangway, crane etc § Safe platform repair work ØLimiting vessel excursion § For position keeping for subsea repair work

Vedam Design & Technology Center MOORING ANALYSIS… CLASH CHECK Ø Platform to barge safe distance Ø Anchor to pipe line distance Ø Across the pipe Ø Along the pipe Ø Mooring line to subsea pipe distance Ø Line to line distance in cross mooring Ø Distance from platform helideck or flare

Vedam Design & Technology Center MOORING ANALYSIS… USAGE OF DP BUOYS Ø DP Buoy parameters for effective lifting of mooring line Ø Location Ø Capacity or size Ø Buoy chain length Ø Catenary shape with effect of DP buoys Ø Optimum usage of DP buoys

Vedam Design & Technology Center MOORING ANALYSIS… LIMITING WEATHER ØAnalysis with extreme weather condition ØDerivation limiting weather condition for safe working condition ØContingency plan beyond limiting weather

Vedam Design & Technology Center MOORING ANALYSIS… RELOCATION ANALYSIS ØTransient Analysis for relocating the vessel ØLine tension and catenary for relocation operation ØWeather condition for safe relocation operation

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