OTC: Experts see ‘new era’ of hurricane activity

May 15, 2006
The US portion of the Gulf of Mexico is in a “new era” of increased hurricane activity that likely will continue “for at least another 15-20 years,” said the lead hurricane forecaster for ImpactWeather Inc. at the annual Offshore Technology Conference in Houston.

The US portion of the Gulf of Mexico is in a “new era” of increased hurricane activity that likely will continue “for at least another 15-20 years,” said the lead hurricane forecaster for ImpactWeather Inc. at the annual Offshore Technology Conference in Houston.

“Hurricanes are basically heat engines-the warmer the water, the stronger they can become. From 1970 through 1994, the Atlantic Basin had been cooler than normal. But in 1995, the waters of the Tropical Atlantic began to heat up,” said Chris Hebert, lead hurricane expert at ImpactWeather, Houston, in a May 2 OTC presentation. “Hurricanes have become numerous and more powerful in recent years.”

The Atlantic Basin includes the Gulf of Mexico, Caribbean Sea, and the North Atlantic Ocean. Previously, the warm waters of the Atlantic would incubate an average of 10 named storms that might blow into the Gulf of Mexico during the annual June-November hurricane season. Of those storms, 6 would become hurricanes, including 2 major ones. However, Hebert said, “There were 15 named storms in 2004, including 9 hurricanes and 6 major hurricanes. The 2005 season broke almost every record for activity with 27 named storms, 15 hurricanes, and 7 major hurricanes. The outlook for 2006 and beyond is not good.”

All of the main climatological and oceanographic signals point to a prolonged period of more frequent and more intense hurricanes along the US Gulf Coast. And like the last period of increased activity in 1926-69, it “may well persist for decades,” Hebert said. “It’s just a matter of time before another large and powerful hurricane impacts the northwest Gulf of Mexico.”

Ivan starts upswing

The 2004 hurricane season registered a significant change as Hurricane Ivan blew across the central gulf in September with winds of 135-140 mph. Measuring instruments on buoy 42040 about 64 nautical miles south of Dauphin Island, Ala., recorded “significant waves” of 50-60 ft, with “maximum waves” estimated at 80-90 ft. “These waves wrought havoc on platforms off the southeast Louisiana coast,” said Hebert. “However, it wasn’t so much the intensity of Ivan’s core as much as the great expanse of hurricane-force winds that produced such large waves.”

Even as Ivan dropped to a Category 3 hurricane on the Saffir-Simpson scale as it approached the US Gulf Coast, its winds extended more than 100 miles from its center. “It had been many years since such a large hurricane had impacted the waters of the northern Gulf of Mexico,” Hebert said.

Since storms as large as Ivan have been rare in the 150 years of recorded storm activity in the gulf, many were expecting storm activity to taper off in the 2005 season. What they got instead was “the most destructive season on record, both offshore and inland” across the northern gulf.

Hurricane Dennis with winds of 155 mph was the strongest hurricane ever to move into the gulf in July. A separate study by Cort Cooper, a fellow in exploration and production research, and James Stear, senior staff engineer with Chevron Energy Technology Co. in San Francisco, found Dennis “had the fifth lowest central pressure on record, despite the fact it occurred near the beginning of the 2005 hurricane season.” Moreover, they reported, “Had it moved another 50 miles west, it would have severely affected the oil patch as well.”

Dennis was followed shortly by Emily, another small but intense hurricane with winds of 160 mph. By late August, weather conditions in the gulf and western Caribbean were more unstable as Katrina became the most powerful Category 5 storm ever recorded in the Atlantic Basin. Again, buoy 42040 measured waves in excess of 50 ft, with maximum waves estimated at 80 ft. “Those large waves, along with Katrina’s powerful and large wind field, caused as much or more damage to offshore platforms across the northern gulf than Ivan,” Hebert reported.

Katrina was followed just 4 weeks later by Hurricane Rita, another Category 5 storm with winds of 175 mph. “Even more unusual, Rita’s wind field was also very large-as large as Ivan’s or Katrina’s. As such, Rita also produced unusually large waves across the northwest gulf production areas, causing additional damage to offshore platforms,” said Hebert.

A separate study by Cooper and Stear of 106 years of data on hurricanes in the Gulf of Mexico indicated that there have never been as many intense storms in such a short period as in 2005. They also discovered from that data “that the intensity of some key storms in the early 20th century was underestimated.”

‘Weak’ evidence of cause

Evidence that global warming may have caused intense hurricane activity in the gulf in 2004-05 “is weak,” said Cooper and Stear. Natural long-term climate variations are “difficult to sort out with a database that contains only about 50 years of reliable data,” they said.

“Dependence of storm intensity on water temperature suggest that the observed ocean warming would only account for roughly a 10% increase in energy,” which would be “far short of the calculated 40% increase in energy” over the time period covered by one recent study that purports to link global warming to increased hurricane activity in the gulf, the Chevron scientists said. Moreover, there are “inconsistencies in the measurement of hurricane intensity over the years,” they said, adding, “Some experts have argued that only in the past decade have intensity estimates been consistently made in most storms throughout the world.”

The pair said a 21-year “time series” study of surface currents in the northern gulf, using infrared satellites developed as part of the National Oceanic and Atmospheric Administration’s “Pathfinder” project “suggests less than 1º C. variation from year-to-year and no obvious increase in 2004-05.” On the other hand, a time series of water temperatures recorded by three NOAA buoys in the central deepwater, western deepwater, and northeast gulf “show no long-term warming trend over the gulf during the 20 years of record, although they do show about a 0.5º C. increase in temperature each year of 2004-05. It is unclear why there is a discrepancy between the satellite results and the buoy results,” they said. However, they concluded, “Even if we chose to ignore the satellite data and assume the buoy data reflected the eastern gulf in 2005, the temperature rise...is just not enough to explain the large number of intense storms seen in 2005.”

Cooper and Stear said, “There are other potential changes from global warming [that] could impact hurricane intensity, particularly in smaller regions like the gulf. For example, the warming of the oceans could be causing slight shifts in the dominant atmospheric steering flow, decreases in vertical shear, etc. None of these changes have been identified in the literature thus far, but they certainly deserve a closer look.”

Until 2002, steering currents across the Atlantic Basin carried most major hurricanes safely out to sea off the US East Coast. “Cooling temperatures in the central and eastern Pacific Ocean may indicate that the Azores-Bermuda high center that dominates the subtropical Atlantic during the hurricane season could strengthen in 2006 and beyond. The effect would be to drive more hurricanes farther westward through the Caribbean Sea and into the Gulf of Mexico or the southeast US Coast,” Hebert said.

Pending further study, said Cooper and Stear, “It can be argued that the jump in intense storms simply represents a chance combination of rare but not impossible events.” In other words, it may simply have been the offshore industry’s collective bad luck.

Hurricane damage

Ivan, Katrina, and Rita-“three of the more severe storms in the past century”-impacted offshore facilities in the gulf “to an extent never before seen,” inflicting “some types of damage not anticipated,” said D.J. Wisch of Chevron. “The shallow-water facilities dominated by fixed platforms exhibited much more damage, not unexpected, than did the deepwater facilities,” he said. “The significance of these storms is not only the unusual size, in terms of storm ferocity and area of impact, but also in the amount of time large proportions of offshore production was offline,” Wisch said. After most hurricanes in the US portion of the Gulf of Mexico, shut-in offshore production was restored to more than 95% of prestorm levels within 7-10 days. However, Wisch said, “It was months before this level was approached” after Hurricane Ivan.

Many government and industry groups are still assessing the impact of hurricanes on offshore operations in the last 2 years. But in its final report on existing offshore damage from Hurricanes Katrina and Rita, which hit the US Gulf Coast in August and September, respectively, the US Minerals Management Service said 79 of the 819 manned platforms in the gulf were still listed as evacuated on May 3, with 324,445 b/d of crude and 1.3 bcfd of natural gas still shut in. That amounts to 21.6% of the crude and 12.95% of the natural gas produced daily from those waters.

Production lost from Aug. 26, 2005, through May 3 of this year totaled 153.2 million bbl of crude and 748.9 bcf of gas. That equals more than 28% of the crude and 20.5% of the gas produced annually from federal leases in the gulf. There has been no accurate count of the amount of oil and gas shut in or the total production lost onshore and in state waters along the Gulf Coast as a result of those storms.

Ivan was the first hurricane to inflict major damage to deepwater operations in the gulf. “The most noticeable damage to deepwater facilities was the dislocated and toppled derrick-mast packages on compliant structures. Three platforms, two spars and a [tension-leg platform], had drilling derrick-mast packages reported to have moved,” Wisch reported. Ivan also triggered submarine mudslides that damaged 12 pipelines of 10-in. diameter or greater. Although damage to those pipelines occurred in relatively shallow water, it shut down production from several deepwater facilities. Wisch said 25% of gulf oil production was still shut in nearly 4 weeks after the storm.

Deepwater facilities hit by Ivan “survived a storm of magnitude much greater than their 100-year design conditions,” he said. The industry also learned “pipeline infrastructure handling deepwater production is very fragile and concentrated in a small area prone to submarine failures,” said Wisch.

Less than a year later, Katrina blew through a little west of Ivan’s previous track. “Katrina destroyed more traditional jacket platforms than any storm in history, and although the storm was of comparable or greater magnitude and spatial size than Ivan, the deepwater facility damage trail left in its wake was considerably less,” Wisch reported.

However, Katrina forced 36 pipelines of 10-in. diameter or greater to be shut in and seriously damaged or destroyed onshore facilities such as gas processing plants, pipeline terminals and hubs. Roads and bridges also were damaged or destroyed, preventing repair crews from reaching many oil and gas facilities.

Compared to Ivan and Katrina, “Rita was almost a nonevent for deepwater facilities,” Wisch said. The capsizing of the Typhoon TLP, which had been working for Chevron in 2,000 ft of water 165 miles south-southwest of New Orleans was the “only notable [deepwater] facility damage” by Rita. But similar to Katrina, Rita damaged 28 pipeline segments of 10-in or greater. “The complicating matter in many of these instances will be the depth should major repairs be needed. The full extent of pipeline damage will likely not be known for a number of months,” Wisch said. “Hurricanes Katrina and Rita leave a number of unknowns, possibly the most anxious being damage to subsea facilities. In recent years the number of subsea developments leading to small diameter flowlines, umbilicals, and bottom founded equipment has increased rapidly,” he said. “Katrina and Rita caused more deepwater drilling units to go adrift than any other storms. How much damage caused by dragging of lines or anchors is still unknown, but the potential is great. Time will tell how extensive, if any, damage to submarine sources will be.”

Lessons learned

“There is little question that these three storms produced loads on deepwater facilities that were greater than their 100-year design,” said Wisch. Yet, he said, “Only one deepwater facility was lost or structurally damaged. This would indicate that for the most part, the design practices and design conditions are in the correct range.”

However, extensive damage to pipelines and onshore facilities indicated a “fragile” infrastructure, “not only from the lost production but also by the lack of options to deliver production to market should a single line or two be out of service,” Wisch said.

“While the global systems, the main structural and station-keeping elements, performed well, significant damage that delay production resumption occurred in other areas of the facilities,” Wisch said. “Some additional work may be desired to be undertaken to better align secondary systems with global performance.”