The world rig market can offer a large and diverse range of units, but relatively few of these are able not only to operate in deep water but also to tackle cold, stormy weather conditions.
So a group of Norwegian investors decided to construct the sensational new Eirik Raude rig, which has been specially designed to work in ultradeep water down to 3,000 meters.
This semi-submersible unit became operational in the autumn of 2002, and was hailed as "the world's most extreme drilling rig" by the Discovery popular science TV channel.
Eirik Raude was put to the test during its very first winter in an inferno of ice, waves and wind off the Canadian east coast.
During this season alone, it faced three 100-year storms. "The first of these blew up on February 27th," reports Halvdan P Strand, operations supervisor on the rig and now stationed in Canada on assignment for the Norwegian owner, Ocean Rig.
"We suffered 120-knot winds and waves 24 meters high. The rig heaved nine meters vertically. A normal unit would have had to abandon the well in weather that bad.
"But Eirik Raude's technology and design ensured that the riser was connected at all times to the blowout-preventer on top of the well."
Mooring to the seabed is extremely difficult when working in 2-3,000 meters of water during stormy weather. Eirik Raude has therefore been equipped with class 3 dynamic positioning.
"This DP3 system ensures that it's relatively easy to maintain the rig over the well, even in violent storms," explains Mr. Strand.
Eirik Raude has been winterized. Much of its piping is equipped with heating cables, making it possible to operate in temperatures down to -20°C.
That permits year-round drilling, saving time and money for the oil companies and giving them greater flexibility.
During its time off Canada, the rig was regularly visited by icebergs large and small. These included one calculated to weigh 1.6 million tons.
"The rig is guarded by up to three supply ships at a time," Mr. Strand reports. "Their job is to push icebergs out of the way to avoid impacts."
Should a berg be on a collision course, the rig can be uncoupled and moved to one side. In emergencies, disconnecting from and securing the well takes just 35 seconds.
Measuring 119.3 meters long by 85.5 wide, Eirik Raude is a little larger than a football pitch of international dimensions.
The rig weighs more than 53,000 tons in normal operation, compared with about 40,000 tons for the fourth-generation Transocean Leader rig.
With a lifting capacity of 909 tons, Eirik Raude can handle up to 10,000 meters of drill pipe and has its own power station generating more than 60,000 horsepower (45 000 kilowatts). Friede Goldman Halter Inc won the contract to build the rig, but this was so complex and costly that the job had to be completed at Halifax in Canada.
Drilling rigs vary greatly in terms of technological outfitting, size and performance, and are usually classified in terms of generations.
The latest units - including Eirik Raude - are defined as fifth generation.
Their technical processes are more automated and operational procedures more efficient than on earlier types.
Hydraulic equipment experiences a reaction time in deep water, so the newest rigs prefer to make use of electronics.
The day rate for a rig of Eirik Raude's class is just over US $200,000. But such units are claimed to establish a well 15 percent faster than a fourth-generation rig.
Mr. Strand believes it will be a long time before another generation of drilling rigs appears, but sees some areas where a sixth-generation type could be improved from the present units.
"I envisage that rigs of the future will be more automated. Lower weight is also likely to be a priority. And heavy steel tubes will probably be replaced by pipes in lighter composite materials.
"That will further reduce costs and open the way to oil drilling in even deeper sea areas."
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