Ugly Boat Becomes Drag Queen

It's the Technology -- Not the Taxi

The seismic vessel Orion isn't much to look at, but looks can deceive.

Look closer -- look past the vintage and more at the value -- and the Orion becomes proof that a vessel doesn't have to be new to be state-of-the-art.

After a major upgrade almost two years ago this Geco-Prakla vessel has been setting seismic records in the Gulf of Mexico -- namely, a new record for the largest seismic footprint using one vessel.

It accomplished that by recording with six 8,000-meter-long streamers with a spread of 1,000 meters, covering a total of 48 kilometers, or eight-square-kilometers.

The most significant aspect of that record is the survey's spread, according to Robin Walker, marketing manager of North and South America for Geco-Prakla.

"We aren't the only company to tow six 8,000-meter long streamers, but this is the first time anybody has achieved more than an 800-meter spread using just one vessel."

Spreads of this size are typically achieved using additional vessels tied to the primary seismic vessel -- a far more costly and complex operation.

While records are nice and make for good headlines, the real story is why companies are working so hard to get such enormous seismic arrays in the water -- and the technology that makes them possible.

These very large spreads are beneficial for two reasons -- economics and data resolution.

"Unit cost is the most important factor of getting that wide," Walker said. "Obviously, covering more area with fewer passes positively impacts the unit cost of a seismic survey.

"This wide spread of long streamers is like a carpet, and with every shot point you fire you are sampling the energy coming back from under the area you cover," he said. "So the more area you cover, the more data you get with each shot point.

"With 3-D seismic you need to cover the whole area," Walker continued, "and because you fire the air guns every 25 to 32 meters, you get a lot of coverage as you move up the line with this kind of footprint."

The Doors

The large spread and long cables also can positively impact seismic data quality, Walker said.

"This survey Orion is shooting is what we call an exploration 3-D survey. The key objective for exploration 3-D is to get low offsets, because the longer the offset the deeper you can sample and get amplitude vs. offset affects and eliminate multiple energy, which impacts the raw data quality.

"It's important to get good quality pre-stacked data," he continued. "Many of our clients want the pre-stacked data for reprocessing and to do detailed pre-stack analysis to look for direct hydrocarbon indicators."

Towing longer streamers in a wider spread might sound like a relatively simple task of merely rolling out more streamers, but it's definitely not that simple.

Image Caption

The Orion may be old and not much to look at on the outside, but inside she's as modern and up-to-date as any ship in the fleet -- and a record-setter. Photos by Kathy Shirley

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The seismic vessel Orion isn't much to look at, but looks can deceive.

Look closer -- look past the vintage and more at the value -- and the Orion becomes proof that a vessel doesn't have to be new to be state-of-the-art.

After a major upgrade almost two years ago this Geco-Prakla vessel has been setting seismic records in the Gulf of Mexico -- namely, a new record for the largest seismic footprint using one vessel.

It accomplished that by recording with six 8,000-meter-long streamers with a spread of 1,000 meters, covering a total of 48 kilometers, or eight-square-kilometers.

The most significant aspect of that record is the survey's spread, according to Robin Walker, marketing manager of North and South America for Geco-Prakla.

"We aren't the only company to tow six 8,000-meter long streamers, but this is the first time anybody has achieved more than an 800-meter spread using just one vessel."

Spreads of this size are typically achieved using additional vessels tied to the primary seismic vessel -- a far more costly and complex operation.

While records are nice and make for good headlines, the real story is why companies are working so hard to get such enormous seismic arrays in the water -- and the technology that makes them possible.

These very large spreads are beneficial for two reasons -- economics and data resolution.

"Unit cost is the most important factor of getting that wide," Walker said. "Obviously, covering more area with fewer passes positively impacts the unit cost of a seismic survey.

"This wide spread of long streamers is like a carpet, and with every shot point you fire you are sampling the energy coming back from under the area you cover," he said. "So the more area you cover, the more data you get with each shot point.

"With 3-D seismic you need to cover the whole area," Walker continued, "and because you fire the air guns every 25 to 32 meters, you get a lot of coverage as you move up the line with this kind of footprint."

The Doors

The large spread and long cables also can positively impact seismic data quality, Walker said.

"This survey Orion is shooting is what we call an exploration 3-D survey. The key objective for exploration 3-D is to get low offsets, because the longer the offset the deeper you can sample and get amplitude vs. offset affects and eliminate multiple energy, which impacts the raw data quality.

"It's important to get good quality pre-stacked data," he continued. "Many of our clients want the pre-stacked data for reprocessing and to do detailed pre-stack analysis to look for direct hydrocarbon indicators."

Towing longer streamers in a wider spread might sound like a relatively simple task of merely rolling out more streamers, but it's definitely not that simple.

"Orion's streamer array is five miles long and the six streamers are 200 meters apart," Walker said. "That's $20 million of spaghetti if it should get tangled up together."

So, the most important pieces of technology to running this kind of spread are the deflectors that keep the streamers separated. Geco-Prakla has patented its own secret weapon, called a mono-wing, that has significantly advanced deflector technology.

The seismic industry generally has borrowed fishing and naval deflector technology. Contractors typically use devices called doors, which are basically curved veins encased in an aluminum or steel frame.

"These doors look like shutters or venetian blinds, and the veins are chained-in at a given angle to achieve the desired spread between streamers," he said. "They are supported by a float and are positioned outside the streamers with the streamers tied to them."

When the doors are deployed they are set at an angle that will keep them in perpetual stall -- so they will go out as far as they can and stall, keeping the streamer taut at that angle.

"The major advantage of the doors is they are inexpensive, but they are also inefficient with a lift to drag ratio of about 2 to 1 -- for every unit of outward force you need one unit of forward force," Walker added. "The resistance also increases exponentially with offset, so the wider the spread, the bigger the doors had to be. And the bigger they get, the harder they are to handle and deploy."

What a Drag

The tremendous drag created by the doors impacts the economics as well. Larger, more powerful boats are necessary to pull the doors -- and those vessels use more fuel as well.

"A few years ago when the industry got to about 500 meter spreads, the doors had gotten seriously big, and our research and development personnel in the towing and handling department felt there had to be a better deflector design," Walker said.

By completely breaking out of the traditional design they came up with the first generation mono-wing.

The first mono-wing design was based on a glider wing shape because glider wings are extremely efficient. The mono-wing basically looks like an airplane wing hanging vertically in the water. The device is attached to a float, and the float is attached to the lead-ins on either side of the steamer array.

One design criteria that was crucial to the initial design was the ability to remotely control the angle of the wing from the boat. The first mono-wing was designed to have just one attachment point to the float, which allows the angle of the wing to be changed in the water.

Also, Walker said, the first mono-wings were far more efficient with a lift to drag ratio of 6 to 1, vs. the 2 to 1 ratio of the older door technology.

"So when you need three times less line drag to get each unit of separation, you don't need extremely large boats burning enormous amounts of fuel," he said.

The mono-wings immediately made 500-meter spreads commonplace -- and to get even wider, extensions were bolted on the wings. These modular units could be taken apart or put together on the boat, allowing the vessel to tow whatever streamer separation was needed.

"With the first mono-wing we got up to 800-meter spreads very quickly, but what we saw at that point was if we were going to get past 800 meters we would have to rethink the design," he said.

"Adding flaps to the mono-wings to achieve more lift also added more drag, bringing the lift to drag ratio down to about 5 to 1. Plus, there were some stability problems at that separation."

Jet-Like Redesign

Geco-Prakla recruited an aeronautics engineer to aid in re-designing the mono-wing, and the new Mk 2 mono-wing was based more on the wing of a fighter jet than a glider.

"This new generation mono-wing is bigger, weighing about 2.5 tons each, but with the advancement in the technology we can really fly the streamers out to the side of the vessel," said Orion's party manager Charlie Law, a British native who oversees all the seismic operations for one of Orion's two seismic crews.

"Orion has tested the technology on a 1,400-meter spread in anticipation of using that kind of spread on the new state-of-the-art Geco Eagle, which will be launched later this year," he said.

All the large 3-D vessels in Geco-Prakla's fleet will be updated with the new Mk 2 mono-wing technology.

The lead-ins that attach the mono-wings and the outside streamers to the boat are another important element in these large spread surveys.

Geco-Prakla tows its deflectors directly off the lead-in vs. a separate cable. This eliminates the drag of cables moving sideways through the water. The mono-wing design requires less tug on the lead-in, allowing the lead-in cable to be narrower -- once again decreasing drag.

The gigantic streamer array Orion is currently towing in the Gulf of Mexico is certainly not applicable everywhere in the world.

"The Orion is shooting a non-exclusive survey in the frontier deep water East Breaks region of the Gulf of Mexico, which is the ideal situation for this kind of spread," Law said. "You have to have these very big surveys in frontier areas to make this kind of enormous spread feasible and cost-effective.

"We shoot 12-hour-long lines before we have to turn," he added, "and believe me, turning this kind of streamer array is a very intricate and time consuming process."

Another critical factor in running these huge streamer arrays is the necessity of keeping the equipment in the water.

"There is over 300 tons of streamers and equipment in a spread like this, so it's imperative that the equipment remain in the water," Walker said. "Both equipment reliability and maintenance procedures are key to achieving this goal ... The streamer array on Orion has been in the water for over a year."

In fact, the equipment's "been out there so long we have to go out in a small boat and scrub the barnacles, seaweed and other growth off the cables to keep from increasing drag," he continued.

"With a spread this big it's a little like painting the Golden Gate Bridge -- when you finish it's time to start at the other end again," Law laughed.

"The survey Orion is currently shooting will be the test to determine if we can keep up the maintenance of this kind of streamer array, and what if any affect that maintenance will have on acquisition operations."

The Ugly Duckling

Of course, the weather is always the big unknown for marine seismic operations, but Geco-Prakla has taken all the steps they can to plan for even weather-related problems.

"Part of the design criteria for all of our systems from the vessels themselves to the streamers is that they can withstand the worse the world can throw at them," Walker said. "All equipment is tested in the winter in the North Sea, and if it can't survive that it doesn't make the entry grade.

"On Orion we won't pick up the streamers unless we are certain a hurricane is going to hit the vessel," Law added. "If it's just a force 10 storm we'll just ride it out -- in fact, one of my biggest concerns is, if we have a hurricane, will we have enough warning to pick up all the streamers?

"It takes days to bring in this much streamer without doing serious damage to the equipment."

The high-tech equipment on board isn't the only notable element of this story. Geco-Prakla has taken a somewhat different approach to adding capacity to its fleet. Rather than continually building new vessels, the firm is turning ugly ducklings like Orion into swans.

"We probably have the ugliest boats in the world's fleet, but we prefer to invest in technology -- not the taxi to get the job done," Walker said.

The company has a vessel design and conversion group in Oslo, Norway, that examined all the Geco-Prakla boats to determine how to get the maximum efficiency and capacity out of each hull.

"We have realized you don't necessarily have to build a new boat to increase your capacity," Walker said.

Orion began life as a pipe barge in the North Sea. It was then taken on by Texaco and converted to a seismic vessel called the Sea Star. Texaco then sold the boat to GSI, and when Halliburton acquired GSI it sold all of its seismic operations to Western Geophysical, included the old Sea Star.

The vessel couldn't keep up with the ever-expanding demands of seismic operations and Western had her derigged.

"At about that same time in 1994 we needed a source boat for undershooting operations in the Gulf of Mexico, and we chartered the vessel," Law said. "It became the biggest gun boat in the world."

It soon came under the scrutiny of the vessel design and conversion group, which determined that a major upgrade could turn the old, worn-out work horse into a powerful vessel.

"I first saw the vessel at the dock in Bergen, Norway, during one of the worse winters we'd ever seen in the North Sea," Law said. "All the lads in the pub laughed about the ugly old tub that kept going out and leaving streamers in the sea. Little did I know that one day it would be my home."

And, upgrading vessels like Orion can mean substantial cost savings.

"For example, we recently upgraded three boats and in the end got one six streamer and two eight streamer vessels for the price of one new eight streamer boat," Walker said. "The Orion upgrade was only about one-third of the cost of a comparable new vessel."

The Geco Eagle, which will be launched later this year, is the first new built boat in the company's fleet since 1993, Walker said, "and yet we've added more than 100 kilometers of capacity to the fleet every year for the last three years through retooling older vessels."

Editor's note: EXPLORER correspondent Kathy Shirley, after enduring a mandatory crash course in survival training, recently spent time aboard the seismic vessel Orion during its current operation in the Gulf of Mexico.

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