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56- www. world- petroleum. org 5.2- Technology: pushing boundaries as much as 28 million cubic metres of natu-ral gas a day from 16 wells - roughly equiv-alent to the consumption of South Korea. The first stage in scoping out the optimal design for a platform is to estimate the field's size, what mix of oil, gas and water it will yield, and how many wells should be drilled. Will it be used just for producing and stor-ing oil or drilling as well? Any platform will have many thousands of tonnes of static load, but the figure's likely to double if a drill-string is included. Water depths and the ex-pected lifetime of the project are other im-portant parameters. And the design will also have to take into account the possibility that yet- to- be- discovered pockets of oil may be linked to the facility in future. Next, bids are let and contractors selected - a daunting exercise in logistics, procure-ment and management. " In an offshore facil-ity there are hundreds of thousands of sub-elements electrical generation, data sup-port, and compressors, for instance," says Bill Dunnett, managing director of offshore Drilling barge: in very shallow, calm waters close to shore, operators sometimes install drilling equipment on a flat- bottom barge that is towed from site to site by tugboats. Jack- up platform/ rig: a jack- up rig is simi-lar to a drilling barge, but has three or more massive legs. After the rig is towed to the site with its legs up, the legs are lowered to the seafloor and then the barge is jacked up so that it rests above the water. When drill-ing is completed, the legs are raised and the platform is towed to the next site. Semi- submersible platform/ rig: the lower hull of this platform has ballast tanks that are filled with water until it is partly submerged with the topsides above the water. Then the platform is anchored to the seafloor. To move the rig, the ballast tanks are filled with air, making it buoyant. Semi- submersibles are typically used for fields in waters at least 60- 90 metres deep. Sea Star platform: smaller versions of TLPs, Sea Star platforms can operate in up to 1,000 metres of water and are typically used to develop smaller deep- water reser-voirs that would be uneconomic to exploit with a larger platform. Fixed platforms: the rigid legs of these per-manent production facilities sit directly on the ocean floor. Fixed platforms are used in water depths of up to 520 metres. Tension- leg platform ( TLPs): long, hollow steel legs extend from these floating pro-duction structures to the seafloor and are anchored to piles driven into the seabed. The legs prevent vertical movement of the platform, but allow enough horizontal motion to minimise stress from wind and waves. TLPs are typically used in waters 450 to 2,150 metres deep. Compliant towers: these drilling and pro-duction platforms are connected to the sea-floor by narrow, vertical towers that are flex-ible enough to absorb the impact of wind, waves and currents. The structures are gen-erally used in water depths ranging from 450 to 900 metres. Spar platforms: the deck of this buoy- like platform, which is designed for deep- water and ultra- deep- water applications, sits atop a giant, hollow cylindrical hull that is tethered to the ocean floor with taut cables and lines. Drill ships: these ships, designed specially for deep- water drilling operations have a drilling platform and derrick on their deck. Drill strings are extended through a moon-hole in the hull and down into the water. The vessels are either anchored or use propel-lers to continually correct their drift, keeping them directly above the well. Floating production system: these plat-forms, typically submersibles or drillships, are positioned over production equipment mounted directly on the seafloor. The pro-duction is pumped to the facilities on the plat-form through flexible pipes called risers. ?? What type of offshore platform does sir require?

57- www. energy- future. com 5.2- Technology: pushing boundaries engineering and operations at Petrofac, an oil field services company. " In addition, there are several thousand sub- contracts on a $ 500 million project." The oil or services company running the project must ensure that all those thousands of bits of kit are compatible with each other, meet the requisite quality standards and that they arrive on time and are - to use a bit of industry jargon - fit for purpose. The late arrival of equipment and materials, or a de-sign flaw, can lead to costly delays and im-pair project economics. Real estate on a platform's deck is ex-pensive, so the engineers are aiming to de-sign platforms that are as small and light as possible, without compromising stability and safety. That means improving layout, min-iaturising equipment, removing redundant equipment or using lightweight construc-tion materials. Sophisticated software pro-grammes have proved invaluable, enabling engineers to create minutely detailed 3- D computer models of a facility before a well has been drilled or a pipe ordered. As well as the on- board facilities - those that separate out the gas and liquids from the production stream, store produced oil and accommodate the crew, for example - scientists are continually looking for ways to reduce the weight of the subsea equipment, from the mooring chains and the risers that carry the oil and gas to the surface to drilling, production and processing equipment. Less weight hanging from the platform = smaller platform = more profitable development. Constructing giants The platform designers' vision starts be-coming reality at fabrication yards, where the structures are assembled by hundreds of welders, fitters, crane operators, paint-ers and riggers. At the height of the oil boom that peaked in mid- 2008, more than 80 rig-building yards - which are usually on wa-terfronts - existed around the world ena-bling the growth of the offshore industry. The yards are immense. The world's largest, a South Korean facility owned by Hyundai, covers 7.2 million square metres. With huge mobile cranes that can lift as much as 1,500 tonnes, giant pieces of equip-ment used to roll flat plate into tubular sec-tions and immense buildings with overhead cranes for working indoors in bad weather, the largest fabrication facilities are as im-pressive as the superstructures they build. And managing them requires broad- rang-ing engineering and technical skills - and teamwork. " For major structures," says Ray 18922009 Gilbert H. Grosvenor Collection