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  • Delving deeper: unlocking offshore


    Shell World 07September 2007 Delvingdeeper:unlockingoffshoreenergy[ ]

  • BY James schofield

    Standing on a deck larger than a soccer pitch, almost 30 metres

    (90 feet) above clear waters teeming with fish, its hard to believe

    the Ursa deep-water oil platform is floating. Theres not a hint of

    movement, allowing the giant structure weighing more than

    57,000 tonnes almost six times as much as the Eiffel Tower

    to safely extract oil and gas from the dark, cold depths over a

    thousand metres below.

    [ ] Delvingdeeper:unlockingoffshoreenergy 07September 2007 Shell World

  • Moored south-east of New orleans, Ursa operates in water almost 1,160 metres (3,800 feet) deep, the equivalent of three empire State Buildings stacked on top of each other. The onboard drilling rig can reach more than four kilometres (2.5 miles) below the sea-bed, grinding through thick layers of salt, rock and densely packed sand to hit targets just a few metres across.

    The Ursa platform shows the extraordinary efforts that oil companies are making to prolong production in the Gulf of Mexico, where reservoirs in shallower water are in decline. It also demonstrates one way that technology is helping oil companies respond to rising demand and concern over energy security: by unlocking previously unreachable deep-water oil and gas deposits everywhere from the Gulf to West Africa and Brazil.

    The lure of the deep is clear. Global reserves in deep water generally meaning depths of more than about 450-500 metres (about 1,500-1,650 feet) are estimated at some 60 billion barrels of oil equiva-lent, enough to supply the USA for about a decade at current demand levels. Thats a tantalising prospect for companies eager to replace the oil and gas they are pumping at a time when easier opportunities both offshore and on are becoming scarcer.

    But working in such difficult locations requires com-panies to overcome a number of tough technical challenges. Some of the most difficult are finding new ways to build these vast floating factories that can venture into ever-greater depths, designing new equipment to work in the intense cold and crushing pressure of water thousands of metres deep, and finding profitable ways to tap reservoirs scattered across many miles. And they have to do all this while keeping costs under control.

    Bigger, deeper... lighterIn mid-May, Ursa is already wrapped in a blanket of suffocating humidity typical during the sweltering summer months of hurricane season in the Gulf of Mexico, when platforms up and down the coast can be battered by fierce storms. Shes one of a breed of platform that has been instrumental over the last

    decade in allowing companies to probe further in deep water.

    Unlike earlier rigid structures that stood firmly on the sea floor, platforms like Ursa float on the surface, getting buoyancy from four giant vertical steel cylin-ders. The platform is secured to the seabed at four corners by 16 immense steel tendons tension legs each weighing almost 900 tonnes, which eliminate virtually any vertical movement. This allows the plat-form to remain stable while supporting thousands of tonnes of equipment.

    every day, Ursa produces enough oil to fill half a million cars and enough natural gas to power more than three million homes. on the production deck the heavy machinery that brings oil and gas to the sur-face and separates it creates a deafening whir. Workers in hard hats wear plugs to protect their ears. The living quarters above the production deck are home to the 120-strong crew, while the tendons and the pipes that bring oil and gas up from wells on the seabed disappear into the dark abyss below.

    But theres a limit to how much weight even this giant structure can bear and remain floating. As a platform moves further out in deep water, it needs longer steel tendons to secure it to the floor and longer pipes that reach down to the wells. These add extra weight and eventually the load would become too much.

    So, as projects have become increasingly ambitious todays are now pushing into waters 3,000 metres (about 9,800 feet) deep and more the industry has gradually turned to a different type of structure called a spar to tap oil deposits out of range of tension leg platforms like Ursa. Spars are not new, but until recent years they were used mainly to store oil close to offshore fields, rather than as full production plat-forms. They also float on the surface, but are buoyed by a single central cylinder that extends about 200 metres (660 feet) under the surface. Solid ballast typically iron ore at the bottom of the cylinder pre-vents tilting and provides enough stability for drilling and extracting oil and gas. Mooring lines hold the spar in place.

    Shell World 07September 2007 Delvingdeeper:unlockingoffshoreenergy[ ]

  • MooredSouth-eaStofNeworleaNS,urSaoperateSiNwateralMoSt1,160MetreS(3,800feet)deep,theequivaleNtofthreeeMpireStateBuildiNgSStackedoNtopofeachother.

    huge ship-mounted cranes are needed to build oil platforms and manoeuvre them into position.

    The tremendous length of such cylinders means their draft is too deep for the relatively shallow water of most shipyards. So the spars decks and equipment must be added in open seas by enormous, ship-mounted cranes. only a few of these exist in the world and must be booked up to three years in advance. This pushes up costs and raises project risks if the construction sched-ule slips, or the weather is too stormy to begin work, costs just keep on rising. Nevertheless, the added reach a spar offers is enough to overcome such drawbacks.

    one of Shells next big offshore projects Perdido will use the spar design in the ultra-deep water of the Alaminos Canyon in the Gulf of Mexico, 320 kilometres (200 miles) south of Freeport, Texas. operating in almost 2.5 kilometres (1.5 miles) of water, the spar will be the deepest spar production facility in the world, able to produce up to 100,000 barrels of oil and

    200,000 cubic feet of gas a day. due to come online around the turn of the decade, it will open up an area of ultra-deep water in the western gulf thought to contain reserves of between three and 15 billion barrels of oil equivalent, according to the magazine Petroleum economist.

    Keeping costs down is key in any project of course, but as tomorrows projects grow in scale and complexity it is becoming increasingly important. drilling rigs can cost up to $600,000 a day to lease at current rates, while a single well can take 60 days to drill. With at least 19 wells, Perdido might have proven too costly to develop. Weight and time cost money in deep water, says Bill henry, Perdidos project venture manager. It can make or break a project. That has forced Shell to find new ways of building the platform.

    [ ] Delvingdeeper:unlockingoffshoreenergy 07September 2007 Shell World

  • one solution is to construct the hull and decks as a single piece instead of as separate modules that are then welded together. This will reduce the amount of steel needed, as well as the construction time. The spar will also include a fully integrated drilling rig. despite adding millions of dollars to the spars price tag, it will save money over time by eliminating the need to lease a more expensive mobile offshore drill-ing rig at todays high prices. having the rig will also make it easier and quicker to maintain the wells from the platform.

    Crushing pressureWhatever structure is used on the surface, the dark depths of todays deep-water projects among the lowest points on the planet so far explored by man present another set of crucial challenges. In these pitch-dark surroundings robotic submarines, oper-ated remotely from the surface, are indispensable. About the size of a car, they carry lights and cam-eras, sharing the icy environment with rarely seen species of fish while conducting the intricate work of installing the complex infrastructure of wells, pumps and pipes on the sea floor.

    The weight of thousands of metres of water bearing down exerts extreme pressure on equipment up to 5,000 pounds per square inch, which is almost 350 times the average air pressure at sea level. Thats enough to crush conventional equipment, so the industry uses special equipment made from extra-thick metal to withstand the pressure. But this means it is extremely heavy, adding to the difficulty of instal-lation. And in the case of the pipes leading to the surface, the extra weight burdens the platform above, limiting how deep it can operate.

    To overcome this, Shell and others in the industry are now developing ways to adapt carbon fibre and other strong, lightweight composite materials already used in other industries such as aerospace. These new, lighter materials, needed for the next generation of projects in ultra-deep water, are likely to be deployed around the turn of the decade.

    crews often over 100-strong work in shifts to keep facilities on

    platforms operating 24 hours a day.

    Shell World 07September 2007 Delvingdeeper:unlockingoffshoreenergy[ ]

  • Scattered fieldsGeology itself provides still more obstacles that deep-water projects have to surmount. While companies always try to pick off the choicest, large reservoirs first, many of todays remaining reserves, both in shallow and deep water, are found in small, separated deposits, rather than single large ones. This means more wells, tens of kilometres apart. If a separate platform were used for each, they would be impossibly expensive to develop. To turn a profit, the fields must be connected together centrally using a single platform. So the industry has developed a new system that allows a number of wells to be drill

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