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Storm Warning PUBLIC ACCESS

Katrina and Rita Pummeled the Gulf of Mexico's Oil and Gas Producers. What can they do to Keep it From Happening Again?

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Mechanical Engineering 128(06), 24-29 (Jun 01, 2006) (3 pages) doi:10.1115/1.2006-JUN-1

This article focuses on measures for preventing damages to oil drilling setups post hurricanes or typhoons. According to engineers, today, it is a complex network of fixed and floating production platforms, mobile drilling units, undersea wells, and oil and gas pipelines. No single solution will ensure the safety of the entire system. The exploration wells under the drilling rigs are also vulnerable. Mobile drilling units, such as jackups and semisubmersibles, which drill test wells and then move to another location, proved especially vulnerable during Katrina and Rita. When the American Petroleum Institute rolled out its first post-Katrina recommendations in April, it took an initial step on a road that will eventually demand changes in everything from air gaps, tie-downs, and deck design to moorings, tethers, clamps, and piping supports. New standards are expected to improve the odds for newer platforms and rigs if they continue to face larger and larger hurricanes.

the day after Hurri cane Katrina scoured the Gulf of Mexico, the residents of Dauphin Island outside Mobile Bay in Alabama came out to assess the damages. In addition to storm wreckage, they found an offshore drilling rig grounded on their beach.

The Ocean Warwick's mangled superstructure towered above the horizon. Ordinarily home to up to 96 workers, its hull measured 208 feet by 178 feet by 23 feet with a 62-foot-square cantilevered heliport jutting out from its side. Its height dwatfed the buildings nearby.

Ocean Wanvick was a jackup rig, a mobile drilling unit that the owner, Diamond Offshore Drilling Inc., could tow to a worksite. Once there, it would lower its legs 300 feet to the ocean floor for support, then jack itself above the water line, and begin drilling. It had been moored 12 miles off the coast of Louisiana. Katrina had pushed it 66 miles to Dauphin Island.

Ocean Warwick was not the only drilling rig to break free. Katrina ripped Transocean Inc.'s $330 million Deepwater Nautilus from its moorings, severing it from the 3,200-foot riser piping that connected it to an underwater well before pushing it 80 miles. The storm tore loose four other drilling rigs and capsized a seventh.

Katrina also wreaked havoc among the production platforms that bring up oil and natural gas from wells sunk into the ocean bottom. It destroyed 46 production platforms and damaged 20 more. One month later, Hurricane Rita took out another 69 platforms and damaged 32 others. Seven months after Rita, 23 percent of the Gulf's oil production and 14 percent of its gas production remain out of conumssion.

Since September, it has been clear that the energy industry must make offshore structures more hurricaneresistant. The vast majority of failed platforms were older fixed units, platforms mounted on tubular steel members supported by piles driven into the seabed. Built as far back as the 1950s and 1960s, they were not designed to today's more exacting standards and also were weakened with age. Katrina and Rita's massive currents, waves, and winds simply ripped them apart. Yet the older structures accounted for no more than 2 percent of the Gulf's total production.

WARNING

The $1 billion, 400-foot-high Thunder Horse platform lists on its side after Hurricane Dennis.Despite defects in its ballats, bilge,and fire water system,the paltform's compartmentalized design kept it afloat.

Grahic Jump LocationThe $1 billion, 400-foot-high Thunder Horse platform lists on its side after Hurricane Dennis.Despite defects in its ballats, bilge,and fire water system,the paltform's compartmentalized design kept it afloat.

Hurricane Katrina damaged Shell's Mars platform in the Gulf of Mexico.it is shown here during reconstruction after the Dutch vessel Hermond had lifted the 1,000-ton drilling rig back into position

Grahic Jump LocationHurricane Katrina damaged Shell's Mars platform in the Gulf of Mexico.it is shown here during reconstruction after the Dutch vessel Hermond had lifted the 1,000-ton drilling rig back into position

The hurricanes also pummeled several modern platforms. Rita, for example, capsized Chevron Corp.'s fouryear- old, $256 million Typhoon, which produced about 40,000 barrels of oil per day plus 60 million cubic feet of natural gas. It now bobs face down, 2,100 feet above the ocean bottom and 165 miles southwest of New Orleans

"Its failure is of great concern to us," said Chevron's senior fa cilities engineering advisor, Paul Versowsky. "We're studying what happened right now, but there's no clearcut smoking gun. It's a huge disappointment."

The Typhoon was very different from the fixed units that work close to shore and constitute one category of platform. Typhoon represents a second category- flo ating platforms designed to operate in deeper seas where supporting truss structures are impractical. Such deepwater platforms now account for 60 percent of Gulf production, and some are monsters.

Typhoon was a tension leg platform, a deepwater floater that relied on tensioned tendons secured to moorings on the ocean bottom to hold its buoyant hull in place. The tension created by the hull pulling up and the tendons pulling down provided the loading needed to drill and produce wells.

A storm can imperil floaters if they break free of some tendons. Then the remaining tendons can cause the platform to behave like a balloon tethered to the bottom of a swimming pool. Any forward motion will push it beneath the surface. Broken moorings may have led to Typhoon's demise.

Weighing in at 36,500 tons of steel, Royal Dutch Shell plc's nine-year-old Mars was also a tension leg platform. One of the Gulf's largest deepwater produ ction platforms, it produced 220,000 barrels of oil and 220 million cubic feet of natural gas each day. Designers built it to withstand 71-foot waves and 140-mile-per-hour winds.

Katrina left Mars looking like a huge fist had pounded the top floors of its superstructure into the lower decks. While Shell has not yet released a report on the damage, several engineers specu late that Mars's drilling derrick was not secmed well enough. When it collapsed, it smashed through the decks and severep the connection with the platform's oil pipeline.

Hurricane Dennis, a less severe storm than either Katrina or Rita, caused extensive damage to BP plc's new $1 billion, 250,000-barrel-a-day Thunder Horse in July 2005 . The platform, destined to become the hub of the Gulf's largest hydrocarbon find, was also a deepwater floater. Its 400-foot-high hull achieved stability by floating partly submerged while anchored to the ocean floor by 16 chain and wire mooring lines

Apparently, Thunder Horse's ballast control valves were installed incorrectly. Operators who thought they were securing the platform prior to the hurricane actually let in water. When they returned after the storm, they found the platform listing at 30 to 35 degrees. Thanks to the platform's compartmentalized design and enclosed decks, it retained enough buoyancy to remain afloat. BP expects to return it to operation later this year.

Pictures of broken platforms and drifting rigs populated the Web for months after the storms, but they showed only part of the story. Below the surface, mud slides, surging currents, and dragging anchors damaged more than 450 oil and gas pipelines, said Alex Alvarado, cheif of the pipeline section for the Gulf of Mexico in the U.S. Department of Interior's Minerals Management Service.

According to Pat O 'Connor, a senior advisor at BP, the production fa lloff after Katrina was not an offshore crisis as much as an infras tructure crisis. " In the past, the industry would recover from hurri ca n es within a few weeks," he sa id . " N ow, we've go t all th ese main pipelines coming in from deepwater fac ilities that feed all the hubs. It's these pipelines that affect production, not the platforms." In addition, Rita damaged many onshore facilities that distribute the oil and gas produced offshore.

The damage to both old and new drilling rigs and production platforms has raised a blizzard of questions about the hlture of Gulf oil production. Are Gulf hurricanes getting stronger? Is storm damage to new offshore units a freak occurrence or a harbinger of things to come? What engineering changes are necessary to ensure future survival? What can be done about undersea pipelines?

The Gulf's growing importance gives those questions added urgency. Until last hurricane season, its 4,000 platforms accounted for 28 percent of all U.S. oil production and 20 percent of natural gas output.

Questions about hurricane performance sparked the American Petroleum Institute, the trade association, to review its standards for offshore oil facilities. The review is not taking place in commonplace standards committee time.

"The emphasis on doing it qui ckly has been phenomenal," said O'Connor, who heads APt's efforts. " I haven't seen anything like it in my 38 years in industry.

"We're not going to get it all sorted out in one year, but we expect to do a lot better than last year," O 'Connor added. "Though that also depends on the storms."

Many industry engineers remain optimistic about the changes needed. "The average age of the 4,000 platforms we have out th ere is about 20 years old, and they turned o ut to be ve ry res ili en t under maj o r storms, " said Charles Sm.ith , a se nior stru ctural engineer in the U.s. Minerals Management Service.

According to Versowsky, "The stru ctures designed to today 's API standards had a very high success rate. Some of th e older units that fa iled dated bac k to 1948, yet many performed well. Steel's a very fo rgiving design tool, and because of cathodic protection and painting above water, those stru ctures can last a long time." Cathodic protection minimizes the rate of electrochemical corrosion of stru ctures such as oil drilling and production platforms, pipelines, and storage tanks.

O 'Connor said of the aging fIxed platforms: "I could have told you which ones would fall down. T he biggest problem we face now is understanding why some are still standing. Sometimes platforms were more conservatively designed or had materi al changes not shown in their records. Maybe someone couldn't get the specified steel so they opted for a better grade. There n1.ay have been local effects involving wave, wind, and current. No matter how much we know, we don't know it all."

O 'Connor also beli eves modern pla tforms have performed well. "There's not a lot of change needed, aside from a better understanding of wave heights and forces," he said. He also lauded the offshore industry for making it through two killer hurricanes without any human casualties or major pollution incidents. (Major pollution incidents are defined as releases of more than 500 barrels of oil. Pipeline breaks released oil, but none exceeded that limit.)

Yet Bob Bea, formerly Shell's chief offshore engineer, is not so sanguine. Bea, an ASME Fellow and now a professor of civil and environmental engineering at the University of California, Berkeley, who specializes in r isk assessment, likened today's isolated issues with new offshore platforms to the warnings NASA received about the Columbia

"I was working on risk assessment for NASA in Houston outside the Johnson Space Center on Febru ary 1, 2003," he recalled. "NASA had seve ral early warnings about the Columbia tiles. They had replaced tiles on shuttles in the past, and so they did something known as normalization of deviants. Instead of treating this as a warning, they said , in effect, 'We've been getting by in the past, so we will continue to get by in the future.' So even when the Air Force drew arrows to missing tiles on satellite pictures, we ignored it.

"On the Gulf, those early stru ctures and pipelines are creakin g and complaining," Bea said . " If we take early, intelligent, corrective action, we ca n probably get home. If we try to ignore them, they'll kill us. I'm pleading for industry and government to recognize the early warnings of an evolving risk."

Bea said that about 80 percent of the offshore structures wrecked by Katrina and Rita were caused by aging. "The other 20 percent represent younger structures with engineering flaws."

The threat to offshore stru ctures comes from two distinct sources: the marine world and the hurricanes th at blow thro ugh it. Each presents disti nct challenges.

When it comes to the ocean environment, most offsh ore engineers would agree with Frank Puskar, president of Energo Engineering Inc., structural consultants based in Houston. "There are still some fIxed platforms from the 1950s and 1960s out there because we use cathodic pro tection to keep corrosion under control," he said. "As long as yo u maintain th em, they can pretty much last indefInitely."

Maintenance is not always a given . " I've been out on platforms where you can stick your hands through the stru cture because of corrosion," Bea said. "N othing protects perfec tly from the mar ine environment. Cathodic protection and painting work fine as long as yo u use the right stuff in the right place at the right time."

"If we take early. intelligent corrective· action. we can probably get home. If we try to ignore them. they'lI kill us."

"I could have told you Which ones Would fall down. The problem is understanding why some are still standing."

Fatigue, often invisible, is also a pro blem in older fixed platforms. The Gulf ordinarily laps gently at structures. Yet su ch common even ts as drops-everything from tools to heavy pumps and winches-and collisions with service boats can accumulate silently as the decades pass.

service boats can accumulate silently as the decades pass. These forces produce what Bea called "old geriatrics," weakened platforms just waiting for storms to knock them over. At the other end of the spectrum are "useful geriatrics," newer platforms with design flaws that might shake excessively. Both are usually positioned over wells whose better days are fa r behind them.

Geriatric platforms might bring up a few hundred barrels of oil per day. At $60 per barrel, though, a well that produces 500 barrels daily generates $30,000 a day, or nearly $1 1 rnillion annually. It makes better eco nomic sense to run the platform until a storm topples it and then pay a few million dollars to salvage the remains .

"As these platforms get weaker over time, they are also growing less valuable," Bea said. "They're subject to judicious neglect. Their operators don 't leave people on them when a storm comes, and they use down-hole safety equipment to keep the hydroca rbons from escaping if there's a platform fa ilure. They may fall over, but no one gets killed and there's no pollution."

This attitude also explains why the vast maj ority of the 115 platforms destroyed by Katrina and Rita were older lllUts that accounted fo r less than 2 percent of the Gulf's to tal production.

What sea and age do slowly, hurricanes do very fast indeed. A key challenge fo r engineers is simply un derstanding the hurr icane forces they must take into account during design.

When platforms first began wading into the shallow waters of the Continental Shelf in the 1950s, they were designed for what the industry called a 25-year return, a storm of a severity that might strike once in 25 years. Engineers figured a platform would see at most one such storm during its 20-year projected lifespan.

Platforms ended up las ting more than 25 years, and storm severity has increased since the 1950s. Since Hurr icane Camille in 1969, the American Petroleum Institute has increased its design criteria several times.

Today, it calls for offshore stru ctures to withstand the fo rces generated by a l OO-year hurricane. T his includes winds with a one-hour average 80 knots (equivalent to a hurricane producing one nunute of sustained 115-mph winds) and wave heights of 70 feet. Some hurricane experts say this corresponds to little more than a Category 3 hurricane, and that some on-shore building codes are stricter. Since 2004, Hurricanes Ivan, Dennis, Katrina, and Rita have all generated one-nunute sustained winds of more than 140 mph.

Are Gulfhurricanes growing stronger? "A lot of tlungs are changing," said Smith of the Minerals Management Service, picking his words carefully. "We're seeing larger storms. The Gulf is somewhat warmer now-whatever the reason-and that's been the main contributor." Five of the 10 most intense Atlantic hurricanes ever recorded slammed into the Gulf during the past seven years.

Allen Verret, executive director of the Offshore Operators Committee, an organization of lease-holders and energy producers on the Atlantic and Gulf Coasts, believes it is more important to focus on the forces an offshore unit must withstand rather than on the storm itself.

"We're revisiting the current standards using what we have learned," said Verret, who cautions against overemphasizing data from 2005 . "We have ocean data from 1950 on," he explained. "It takes a large database of significant occurrences to change our design basis. One year of data alone is totally useless. That's not how codes are built." Still, Verret expects future standards will require platfo rms to resist significantly greater forces, with the largest increases assigned to the most intense storms.

Produ ction platforms are especially vulnerable to waves. Wind will blow through their open four- or fivedeck structures. If a wave breaks over a platform, though, it acts like a hammer striking a flat plate. Tons of water can twist and turn a platform and possibly overturn it.

In the 1980s, designers looked at accumulating storm da ta and increased the air gap between the lower deck and the ocean. Where platforms once allowed 40 feet of clearance, they now sit 50 to 70 feet above the water. "A lot of smaller fixed platforms were destroyed by Katrina and Rita when waves hit the deck," Puskar, the structural consultant, said. "They're lying on the bottom of the sea now." Platforms with higher decks -survived.

Over the years, Puskar said, engineers have made platforms higher and also stronger. Structural members have grown stronger and thicker. "There's always been a fair amount of conservatism in design," he said. "We'll dig foundations 300 or 400 feet under the mud line and overbuild the structures."

In the past, designers focused most of their attention on waves. According to Snuth, " Little time was spent on securing topside operating equipment, such as stairwells, grating, equipment on decks, and helidecks." The wind damage caused during the last few hurricane seasons has encouraged the Minerals Management Service to revisit tie-downs.

"We're looking at better ways to secure drilling rigs, living quarters, and equipment so they don't get washed off the deck," Smith said. "This is especially a problem on some floating facilities, which are compliant structures designed to move back and forth. Tt's the old equation of fo rce equals mass times acceleration. These structures act like a wlup and when they snap, things break."

The derricks and masts used to position drilling equipment and risers are especially vuln erable. They are complex stru ctures built to support millions of pounds of drill pipe, pipe collars, control cabling, and drill bits descencling hundreds or thousands of feet to the ocean floor.

"The simple an swer is to make them stronger and tougher," accorcling to Bob Bloom, the chief technology officer of National Oilwell Varco Inc. in Houston, which makes derricks and other platform equipment. "But if you make it stouter, that throws lots of weight onto the vessel. Builcling massive structures on fixed platforms transfers the load to the ocean floor. On floating vessels, you add more weight than the hull design can accommodate.

"As weight rises, it has an effect on other rig components. So you can't just make things stronger in isolation. There has to be a total review of the vessel, from derricks to platforms to lllooring systems."

Hurricanes are strong enough to snap drilling rigs like Ocean Warwick from their moorings and drive them dozens of miles off station. Mobile drilling units, such as jackups and semisubmersibles , whi ch drill test wells and then move to another location, proved especially vulnerable during Katrina and Rita.

"Several broke free of their moorings during the storms," Puskar said. He said there is a risk that they could capsize, crash into stationary platforms, or drag their anchors across the pipes that crisscross the bottom of the sea.

The obvious an swer-adding more mooring lines-is not always the right solution, Verret said. Adding mooring lines adds weight. Tlus reduces a vessel's buoyancy and its ability to support the weight of deep drilling equipment. Nor do additional mooring lines provide more stability. " It doesn't mean it will survive or stay on station," Verret said. "You could make it so stout, it would just blow over.

The exploration wells under the drilling rigs are also vulnerable, according to O 'Connor. When a hurricane approaches a jackup rig drilling an exploratory well, the j ackup will release the well to lift itself higher above the water for safety. "Then the well 's on its own, and that's why th ey're blown over by the hurri cane," he sa id. "Maybe we need to start supporting those wells with a steel structure of their own."

Pipelines present many problems. They are usually buried three feet under the mudline, often encased in concrete for extra ballast and secured with steel anchors or screws. "Historically, pipelines have not been a major problem," said Alvarado of the Minerals Management Service. This past season, though, powerful waves precipitated mudslides in the light soil where the Gulf drops off shar ply into deeper water. Farther out, dragging anchors ripped thro ugh pipes . According to Alvarado, 450 pipelines were damaged.

Bea has focused his attention on the shifting sea floors near the Mississippi delta. "The sediment has the consistency of pancake batter, and there are moving secliments as deep as 100 feet," he said. "You don't want to dig that deep. Instead, we could route pipelines away from problem areas or build pipelines with fu ses that let the line break safely in weak areas."

Over the past 50 years, the Gulf of Mexico has become a dynanlic oil producing system. It has grown in capacity economic importance, and complexity. Today, it is a complex network of fixed and floating production platforms, mobile drilling units, undersea wells, and oil and gas pipelines. No single solution will ensure the safety of the entire system.

Still, when the Ameri can Petrol eum Institute rolled out its first post-Katrina recommendations in April, it took an initial step on a road that will eventu ally demand changes in everything from air gaps, tie-downs, and deck design to moorings, tethers, clamps, and piping supports. New standards certainly won't save facilities that have outlived th eir productive years. Those fi xed platforms will be left to di e. But new standards may improve the odds for newer platforms and rigs if they continue to face larger and larger hurricanes.

Can they prevent another capsizing or deck collapse? Will they keep another rig from running aground on a fa raway beach? Perhaps. It depends on how well the industry understands the forces nature throws at it, and how well its engineers meet those challenges. And it depends on the weather.

Hurricane Katrina pounded the Ocean Warwick's super structure,ripped it form its moorings,and dragged it 66 miles before running the drill aground in Alabama.

Grahic Jump LocationHurricane Katrina pounded the Ocean Warwick's super structure,ripped it form its moorings,and dragged it 66 miles before running the drill aground in Alabama.

Copyright © 2006 by ASME
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