Old Oil Rigs

OLD OIL RIGS NEVER DIE Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/141/11/36/6452524/me-2019-nov2.pdf by guest on 26 September 2021 From reinstallations to artificial reefing, obsolete oil platforms gush out new ideas for reuse. BY LINA ZELDOVICH iles away from the shore in the open ocean BCG has identified several other emerging decommis- stands an oil platform towering above the sioning hotspots around the world. Southeast Asia is the M water like a skyscraper. There is little oil left largest of them, with more than 1,500 structures and in the well beneath it, and the platform is nearing the end 7,000 wells. Over the next 20 years, however, the Persian of its working lifespan. Although it remains firmly moored Gulf is likely to have more shutdowns, since it has 1,000 to the ocean floor, something is about to happen. structures and 3,000 wells that will be more than 30 years A small, submarine-like vehicle descends along the old by 2038. tower that anchors the top deck to the seabed, a dia- In the Gulf of Mexico, where the United States Bureau of mond saw clipped onto its sturdy metal leg. After some Safety and Environmental Enforcement (BSEE) oversees radio exchanges, the saw comes to life and it begins to decommissioning, operators and contractors have been eat steadily through the metal. The small fish, disturbed removing about 150 to 250 structures a year since the by the unusual activity, scatter. The platform takedown 1980s. This makes the Gulf—where offshore production begins. began—the region most experienced with decommis- Offshore oil and gas platforms are among the largest sioning. structures humanity has ever built. There are more than Yet more challenges lie ahead. The shallow waters 7,500 of them towering up from seas all over the world, of the Gulf’s continental shelf have been thoroughly ex- according to some recent estimates. As wells dry up and ploited since 1937, when the predecessors of Chevron pumping equipment wears down, those structures are and ExxonMobil teamed up to build the first true offshore likely to become obsolete in the upcoming decades. platform, a modest pumping facility in 14 feet of water lo- But producers cannot just walk away from their cre- cated one mile off the coast of Louisiana. Within 10 years, ations. Those oil wells will have be decommissioned and production had moved 20 miles from the shore, though capped off and the platforms taken down. It will be a vast water depth was still only 18 feet. effort. In Europe’s North Sea, where production has de- BCG estimates that operators will have to remove more clined to 1.5 million barrels per day from 6 million barrels than 2,000 structures. They tend to be further offshore per day in its prime, decommissioning could cost produc- and an order of magnitude heavier than previous than ers $150 billion, according to a recent report by Boston previously decommissioned platforms—think 12,000-ton Consulting Group (BCG). structures in waters more than 330 feet deep. 1119_MEM_Deconstructing Offshore Platforms.indd 36 10/9/19 8:59 AM NOVEMBER 2019 | P.37 Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/141/11/36/6452524/me-2019-nov2.pdf by guest on 26 September 2021 Massive Brent Bravo oil platform makes dramatic arrival into Hartlepool's Seaton Port to be recycled. Photo: Shell 1119_MEM_Deconstructing Offshore Platforms.indd 37 10/9/19 8:59 AM Bluegrass engineers designed a 15’ underwater diamond wire saw. The saw was built in their machine shop and customized specifically for the challenges of dismanteling oil rigs. Photo: Bluegrass Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/141/11/36/6452524/me-2019-nov2.pdf by guest on 26 September 2021 The North Sea is gearing up for an even steeper challenge. It legs and cross-bars to hold it steady, whose foundations are has about 600 platforms and more than 7,000 wells to decom- driven into the seabed. Deck-tower structures account for the mission. Some of those structures are an order of magnitude vast majority of aging platforms. larger than those slated for decommissioning on Gulf of Unlike floating platforms, which can be towed anywhere Mexico, and they sit in deeper water as well. once their moorings are loosened, deck-tower systems are For example, certain structures in Shell’s Brent field, located permanent structures. Each platform is essentially unique, and in the East Shetland Basin of the North Sea, weigh 330,000 cutting and disassembling them is as much an art as it is a sci- tons—the equivalent of the Empire State Building, according ence. The job often requires remarkable feats of engineering, to Duncan Manning, decommissioning manager for Royal combining new types of saws with deep-diving subsea robots. Dutch Shell’s Brent field. A typical takedown begins with dismantling the top But taking down an offshore oil platform and the tower that platform, which usually hosts production equipment, living supports it is no simple assignment. It is a massive engineering quarters, and a helicopter pad for bringing in crew and sup- project that requires state-of-the-art equipment. plies, said Chris Mattingly, a project manager at Bluegrass, a company that specializes in “nonexplosive demolition.” This A SCIENCE AND AN ART usually means cutting concrete and metal structures with Oil platforms come in many types and sizes. Those designed diamond-studded saws. for the deepest waters float on the surface, stabilized by ballast “It starts out with a crew of welders and they take down as and held in place by tension cables anchored to the sea floor. much of the top side as they can,” Mattingly said. “Then we More common, however, are structures designed for shal- get involved with our diamond wire saws, cutting steel mem- low waters near shore. These consist of a deck resting on top bers and piping, to get the top sides off—which is everything of a so-called jacket, a metal tower typically comprising four you see above water.” 1119_MEM_Deconstructing Offshore Platforms.indd 38 10/9/19 8:59 AM MECHANICAL ENGINEERING | NOVEMBER 2019 | P.39 Sometimes the weather is nice. A Stinger ROV is reflected in calm seas during underwater inspection of a fixed oil installation in the North Sea. Photo: Stinger Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/141/11/36/6452524/me-2019-nov2.pdf by guest on 26 September 2021 The retired Williams platform, located 60 miles off the coast of Alabama, was recently disassembled into two massive pieces. The 3,600-ton topsides was lifted and placed on a transportation barge to be sent to shore for scrapping, while the 1200-ton steel frame supporting the deck, 300 feet under water, will become an artificial reef. Photo: Pipe Up, The Williams Blog Bluegrass is best known for pioneering the diamond saws it structures can be reused in another oil field. Companies uses, and it invented the first practical underwater diamond from Vietnam, Thailand, or China sometimes buy the old saw. Expectedly, these instruments do not look anything like structures and re-install them over their own oil wells, garage saws or chain saws. Mattingly said. Instead, they resemble calipers outfit with pulleys. The cut- In that case, the team preserves the entire tower structure. ting edge consist of long wires studded with diamond beads The four legs, usually 4-inch diameter each, are cut at the very and pulled around the pulleys by a hydraulic motor. The beads bottom and the jacket is lifted onto a barge in its entirety. steadily rub against the material, applying the force of friction “Imagine if you had a tree house in your backyard and you to the surface to efficiently cut any material, from reinforced sold it to your neighbor,” Mattingly explained. “You would just concrete to titanium. cut the posts at the bottom where the grass is, and he would The placement of the saw depends on the depth of the just pick up the whole tree house, take it into his yard and set water. In shallow waters, a human diver mounts the saw on it back up.” the metal or concrete struts with a hydraulic clamp to keep Other times, it makes sense to scrap the jacket entirely. In it in place. Then an operator controls the cut by regulating that case, Bluegrass or a similar contractor will cut the tower hydraulic power from a workboat. into smaller pieces, usually 10 to 20 foot sections that are then “In the Gulf of Mexico, often the water is shallow enough loaded onto barges and shipped to shore for recycling. that you can use a diver,” Mattingly said. “Anything deeper The exact depth at which they cut the legs depends on how than 300 feet requires a remotely operated vehicle, or ROV, the ocean area will be used once the structure is gone. Clearly, essentially a small submarine.” the presence of oil and gas platforms restricts boat traffic and Exactly how and where the jacket is cut depends on what commercial fishing because of the risk of collision and pipe- will be done with it. In some cases, these robust long-lasting line damage. 1119_MEM_Deconstructing Offshore Platforms.indd 39 10/9/19 8:59 AM With the platforms gone, however, planners can reopen that ocean area, but its intended use will determine the final stage of decommissioning. If they plan to use the area for fishing— and in the Gulf, that often means shrimping—the platform legs must be cut below the ocean sediment level, or “mud level.” Otherwise, metal scraps poking through the ocean bottom would catch and destroy shrimper nets, which scrape the bot- Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/141/11/36/6452524/me-2019-nov2.pdf by guest on 26 September 2021 tom of the sea.

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