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January 2012 www.sname.org/sname/mt As water depth increased, the scope and resulting line tensions and weight of the moor- ing system became a large added load on the hull of the FPU. e earliest mooring systems were either all chain, or used chains in the upper and lower portions with wire ropes in between. At moderate water depths, conventional systems provided good station-keeping capa- bilities. Catenaries mooring systems had several disadvantages for ultra-deepwater develop- ments: extremely large seabed footprint, heavier vertical loads on the facility, and higher demand on the mooring hardware. To solve these issues, semi-taut and taut mooring systems were devel- oped and have been adopted along with suction anchors, which are installed for better handling of the vertical mooring forces near the mud line. Polyester mooring systems for deepwater facilities, considered novel technologies ten years ago, have been qualied and accepted as mature technology and are standard for recent nished and ongoing projects. BP?s Mad Dog, Anadarko?s Red Hawk, Chevron?s Tahiti, Shell?s Perdido, and Chevron?s Jack & St. Malo projects all have employed polyes- ter taut-line mooring systems. Risers are the conduits between the subsea wells and the surface facilities. As water depth has increased, strength, buckling, and fatigue issues associated with risers have become real challenges. e motion coupling characteris- tics of risers and oating production facilities have been studied extensively and are still under research. To resolve riser design issues in ultra deepwater, many new ideas have been proposed. Notable systems are the top-ten- sion production risers, exible riser pipes, and steel catenary riser (SCR) systems with subsea buoyancy modules (lazy wave conguration). Free-hanging risers made of special steel and in centenary forms, SCRs have become the norm for oil and gas exports, and well streams. Before the recent three big hurricanes in the Gulf of Mexico?Rita (2005), Katrina (2005), and Ike (2008)?most production facilities were designed to survive a 100-year return period hurricane. These storms col-lectively caused billions of damages to the Gulf Coast facilities and properties. Industry groups conducted post-hurricane analysis of available storm wave records and realized that the recorded wave heights were much larger than predicted and expected. In many cases, wave heights approached 500 year or greater levels. is meant that the design cri- teria for oshore structures in the gulf had to be increased to higher return period, such as the 1,000-year period. e U.S. federal government has since imposed more stringent design and assessment criteria for both new and existing oshore facilities including mooring systems. Classication societies have also required that additional survival environmental criteria be specied in the TLP and semi designs. Incidents aecting the evolution of FPUs e oshore oil and gas industry is a risky busi- ness in terms of the investment involved, as well as the risks associated with every step during exploration, production, and transportation. Various types of accidents have happened to both drilling rigs and production platforms. Hurricanes in the Gulf of Mexico have caused substantial damages to oshore pro- duction platforms, including derrick collapse and total loss of the unit. One such incident in the U.S. Gulf of Mexico was the listing of the Thunder Horse drilling and production platform following the passing of Hurricane Dennis in 2005. Although the wind and wave impacts were relatively moderate, the unit listed some 16 degrees. Fortunately, the buoy- ancy from the under Horse hull deck box, the upper portion of the hull, helped save the production platform. Without the deck box, the under Horse facility could have listed even further and possibly sank. Findings and lessons from this incident included better inspection of ballast systems during construction; no exter- nal ballast system openings in the below-water hull; and better control of ballasting operations. In another incident that same year, Hurricane Rita destroyed or damaged many platforms. Chevron?s Typhoon MiniTLP was such a total loss example. It was reported that a drifting platform was suspected to have collided with the TLP and somehow caused the loss of tendon tension, leading to a capsize. Although the ndings from this incident report were not conclusive due to a lack of witnesses, it was believed the storm conditions exceeded estab- lished design codes. e industry responded by establishing an API committee to review Gulf of Mexico hurricane metocean criteria, and new criteria were proposed and adopted in 2008. Although these incidents are rare, they have led to changes in the way operators and designers view the safety of oshore opera- tions, leading to fundamental changes in design features. To minimize the risks of accidents oshore, operators, classication societies, and platform designers have worked over the past 30 years in various aspects and capacities. Operators have increasingly stressed the importance of safety in design by incorporating new rules and internal specications into their new projects, while designers have come up with various ideas to mitigate risk and improve design. Most operators have engaged the facility operations personnel during project development, from the early stage of the design. is helps to familiarize the operators with the design and to identify and ?design out,? or minimize, potential hazards and risks before the facility is in operation. Systems design Buoyancy distribution is a critical issue for semisubmersible hulls, as they are quite sensitive to payload and center of gravity changes. One system used on a number of LEARN MORE Fþÿ o rOR þÿ aADD þÿ i t i oITIO Nþÿ a lAL þÿ iINþÿ f o r m a t i oFORMATIO N þÿ oON þÿ tTHþÿ eE þÿ f l o a t iFLOATI Nþÿ gG Pþÿ r oRODþÿ u c t i oUCTIO N þÿ uUNþÿ i tIT þÿ s e c t o rSECTOR , þÿ cCHþÿ e cEC K þÿ o u tOUT þÿ tTHþÿ e s eESE þÿ s o u r c e sSOURCES þÿ u s eUSE D þÿ bBY þÿ tTHþÿ eE þÿ a u tAUT Hþÿ o r sORS :?2011 Worldwide Survey of Semi-FPSs and FPSs,? Oshore magazine, January 2011 ?Floating Production Systems: Past, Present and Future Technology,? Society of þÿ NNaval Architects and Marine þÿ EEngineers, Transac- tions 1993 ?þÿ H History of Oshore Oil and Gas þÿ DDevelop- ment in the Gulf of Mexico,? Bureau of Ocean þÿ EEnergy Management, þÿ RRegulation and þÿ EEnforcement, July 2004 ?þÿ HHistory of the Oshore þÿ IIndustry,? Oshore magazine, October 2007 ?Project Mohole,? þÿ NNational Academies, 2005 ?þÿ IInterim Guidance for þÿ DDesign of Oshore Structures for þÿ HHurricane þÿ CConditions,? AP þÿ II Bulletin 2þÿ I NINT-þÿ DDG, rst edition, May 2007. 32_37_Praughtfeature_SNAME_Jan12_P3.indd 3612/22/11 3:39 PM