New Mission Helps Offshore Industries Dodge Swirling Waters

Feature July 1, 2008


New Mission Helps Offshore Industries Dodge Swirling Waters

Hurricanes aren't the only hazards spinning up in the Gulf of Mexico -- they have a liquid
counterpart in the waters below called ocean eddies. Offshore industries, such as oil and
gas companies, have to keep a weather eye on both. In a worst-case scenario, they could
find themselves caught between the two. Satellite altimetry is helping government and
industry manage those risks.

Satellite ocean observations are a standard part of marine operations around the world.
Keeping track of local currents is critical for daily operations. And in the Gulf of Mexico,
that means knowing the location of the Loop Current and its dangerous eddies.

The Loop Current, which is part of the Gulf Stream, begins as a large flow of warm water
from the Caribbean. It heads up into the eastern part of the Gulf of Mexico, then turns
south and finally moves out through the Straits of Florida. Deep and fast moving, the
Loop Current often breaks off and forms strong, clockwise rotating eddies called
anticyclones that travel westward into the Gulf. The currents along the outer edges of the
Loop Current, as well as these eddies, have been clocked at speeds as high as three to
four knots (three to five miles per hour), comparable to the fastest ocean currents ever
observed.

Because the Loop Current and its eddies are warmer, and thus higher in surface elevation,
than the surrounding waters, they are easily spotted by satellite altimeters, such as those
aboard the NASA/French Space Agency Jason 1 and Ocean Surface Topography
Mission/Jason 2 satellites. To see what the altimeters see, many offshore operators turn to
Research Professor Robert Leben and his colleagues at the University of Colorado's
Center for Astrodynamics Research in Boulder. They use the latest satellite
measurements of sea-surface height from Jason 1 and two other satellite altimeters to
create maps showing the location, direction and speed of currents in the Gulf of Mexico.
Free and available on the center's Web site, these maps are used by a wide variety of
people involved in marine operations, along with scientists, fishermen and sailors. As
soon as measurements from the Ocean Surface Topography Mission/Jason 2 are
available, they will be included in the data sets as well.

For oil companies, knowing where the Loop Current and its eddies are and are likely to
go is critical. "The rate to rent a drilling rig in deep water is about $300,000 a day," said
George Forristall, of Forristall Ocean Engineering, Inc., Camden, Maine. "If you've
planned an operation and the current is too strong, you have to shut down and spend that
money without accomplishing anything. Once an oil field is found and a permanent
facility is built, it floats on the surface and connects to the bottom by pipes called risers.
You can protect those risers by streamlining them, but that costs a lot, too. Your riser
design has to be appropriate for the currents you expect at your site."

To plan and design rigs and oil platforms for the future, oil companies would like to be
able to anticipate the sea conditions a particular facility may encounter in the Gulf of
Mexico over its lifetime. A consortium of about 20 different companies, along with the
U.S. Minerals Management Service, has asked Leben and Forristall to develop a model
to help determine what the risks from strong currents may be.

"We're constructing a 1,000-year-long statistical simulation of the Loop Current and its
eddies," said Leben. "While we have only 20 to 30 years of observations, using
computer simulation and the right statistical methods, we can figure out how the current
and eddies behave and then simulate a longer period of time."

"It's a modeling technique called Monte Carlo simulation," he continued. "For example,
even if you don't know exactly how dice work, after a number of throws, you can figure
out the probabilities for certain numbers to appear."

"The idea," said Forristall, "is to map the Gulf. There are some places where there have
only been a few eddies in the past. With our artificial time series, we'll be able to fill in
the gaps. We'll be able to see what is the likelihood of an eddy occurring in a particular
spot."

Another goal of the effort is to better understand the relationship between the Loop
Current and hurricanes, which grow stronger as they pass over warm water. Leben said
results of the 1,000-year Loop Current simulation will be combined with simulations of
how the Loop Current's warm surface waters and eddies effect hurricane intensification.
"This will give us a way to assess the likelihood of warm Loop Current events and
intense hurricanes and plan for them."

"These tandem ocean/atmosphere events are rare, but they do occur," said Leben.
"During Hurricane Katrina, when both strong eddy currents and a category-five
hurricane hit the oil patch in the north-central Gulf of Mexico, a total of five rigs and 18
platforms were lost and many more were damaged."

Knowing more about the Loop Current and its spinning offspring will help oil companies
and other offshore industries plan for the future. "Nothing designed by man will ever be
perfectly safe from natural hazards," said Forristall, "but the better we understand the
environment, the better we will be able to manage risk at an acceptable cost."

For more information on OSTM/Jason 2, visit: http://www.nasa.gov/ostm .

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