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Vol. 15, No. 12 Week of March 21, 2010
Providing coverage of Alaska and northern Canada's oil and gas industry

Arctic Directory: A new Arctic paradigm

Moving farther north in Arctic offshore stimulates drilling safety innovation

Alan Bailey

Petroleum News

The potentially huge but largely untapped oil and gas resources of the Arctic offshore have become a major focus of attention, as access to new resources in traditional petroleum provinces has become ever more elusive. But, as exploration moves north into deep Arctic waters, it will become increasingly difficult to use the drilling of a relief well as the mechanism of last resort for plugging an oil well blowout, Bill Scott, manager of Chevron’s Arctic Center in Calgary, Alberta, told the U.S. Minerals Management Service Arctic Technologies Workshop in Anchorage, Alaska, on Oct. 15. A relief well is an emergency well drilled to penetrate and plug a well that is out of control.

Given the potential problems in relief well drilling in deep Arctic waters, Chevron is seeking new ways of proactively preventing a blowout from occurring.

“We want to go one stage further at the front end, to stop any problems happening later,” Scott said.

Floating rigs

But what are the risks associated with modern offshore exploration?

Most new Arctic offshore exploration drilling is done in water depths that require the use of a floating drilling rig, a drilling approach that has become the technique of choice in the Arctic offshore of Canada and the United States, Scott said. And so far, the safety record in using this technique in the relatively shallow waters of the Chukchi and Beaufort Seas has proved exemplary, with five wells in the Chukchi Sea, nine wells in the U.S. Beaufort Sea and 39 wells in the Canadian Beaufort Sea having been drilled to date from drilling vessels, he said.

“They were completed both safely and successfully in periods from 100 percent daylight to 100 percent darkness,” Scott said. “We achieved all of our goals without any serious incident.”

But, although modern drilling techniques have rendered the possibility of an accidental, uncontrolled oil blowout extremely unlikely, government regulation and prudent safety both require a well operator to maintain the capability of drilling a relief well.

Increasingly challenging

However, as drilling operations take place progressively farther north from the Beaufort Sea coast, moving off the shallow offshore shelf into ever deeper water where the shelf slopes down toward the Arctic Ocean floor, in situations where drilling targets also become deeper and more challenging, the need for longer drilling times combined with the short open water seasons of the extreme north will severely limit the practicality of relief well drilling.

In fact some wells may take more than one season to drill, thus raising question marks over the possibility of drilling a relief well in any feasible time frame.

“It’s going to become increasingly challenging to be able to drill a relief well,” Scott said. “… We’re now looking at wells that take two to three seasons to drill, so obviously the ability to continuously drill a relief well in those areas is challenged, if not impossible.”

And under Canadian regulations, drilling in the Beaufort Sea has to be completed by or on Oct. 15, thus making a blowout that occurs right at that Oct. 15 date the worst case scenario for the loss of control of an oil well, Scott explained. Subsequent relief well drilling would have to be done at a time of year when daylight is dwindling and the winter sea ice is starting to form.

“So the longer it goes into the winter period, the tougher it is to get things done and tougher it is, certainly, to get them done efficiently,” Scott said.

And, although the probability of a well blowout nowadays is as low as perhaps one in 300,000, a contingency plan that includes the possibility of drilling a relief well must assume the possibility of a blowout occurring: Relief well drilling must be feasible, Scott said.


Chevron has developed a computer simulator to model the conditions under which a late-season offshore relief well might be drilled. The simulator can test the feasibility of relief well drilling at different distances offshore, north of the Canadian Beaufort Sea coast.

Data from the past 10 years indicates that on the relatively shallow continental shelf 73 to 100 days would be available to drill that worst-case scenario relief well, with the relief well likely taking about 60 days to drill.

“The conclusion obviously is that a relief well could be drilled,” Scott said.

But, farther north in the Beaufort Sea, out on the continental slope, only seven to 67 days would be available for relief well drilling, in a situation perhaps requiring 120 days to plug the uncontrolled well.

“Obviously, somewhere between the shelf and the slope we run into a problem which is a combination of well depth, ice conditions and equipment, where it becomes, in all likelihood, impractical to drill a relief well,” Scott said.

However, the Canadian drilling regulations allow an alternative contingency arrangement to be substituted for relief well drilling, provided that this alternative arrangement represents an equivalent or lower risk than that associated with a relief well. That “equivalency” clause in the regulations has led Chevron to seek new techniques for handling blowouts, a search that has led to an initiative with a drilling equipment company, Cameron, to develop a new form of blowout preventer.

“We’ve decided to go for an equivalency to late-season relief wells, and we see the need for that in various Arctic nations. … We’re developing this technology for worldwide use,” Scott said.

Key technology

The key technology in the new blowout preventer design is a hydraulic ram that will both shear and seal the well tubing — a conventional blowout preventer has separate rams for the shearing and sealing operations.

“A single ram will do what two rams did — it will shear and seal simultaneously,” Scott said.”It will cut and seal on a wide variety of drilling tubulars and production casing.”

The stacking of two of the new rams in a single blowout preventer will provide 100 percent redundancy in both the shearing and sealing operations, while additional rams and other technology in the massive device will further increase the device’s overall effectiveness.

Testing of the new blowout preventer design is scheduled for the fourth quarter of 2009, with testing likely to be completed in 2010. And, in addition to being used on wells drilled from floating rigs in the Arctic offshore, presumably with the blowout preventer located in the seafloor, the new design could find application in other situations, such as drilling from offshore platforms and from land rigs. However, given the difficulty of trying to shoehorn a huge new blowout preventer into an existing land rig, for example, Chevron is considering developing a safety package, using the new technology, for retrofitting into existing rig configurations.

But, when it comes to using new technologies such as the new blowout preventers in the Arctic offshore, Chevron is taking great care to discuss its proposals both with government regulators and with the local communities along the Canadian Beaufort Sea coast, making sure that everyone is on board with what Chevron is proposing, Scott said.

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Drilling mud-line cellars for OCS drilling

A blowout preventer, a tall stack of valves and other devices designed to rapidly shut down a well in the event of an oil blowout, is an essential piece of safety equipment that has to be installed at the surface end of a well whenever a drilling operation is in progress. And when drilling on the outer continental shelf, the blowout preventer would sit on the sea floor.

But in the Arctic offshore, such as on the outer continental shelf of the Beaufort and Chukchi seas, the prevalence of sea ice, much of it in constant motion, gives rise to the possibility of an ice keel hitting a blowout preventer, causing major damage to the device and raising the risk of an oil spill.

To avoid this eventuality, all blowout preventers on the Arctic OCS have to be installed in mud-line cellars, cylindrical holes in the sea floor, typically 40 feet deep, Cody Teff, Shell engineering team lead in Alaska, told the U.S. Minerals Management Service Arctic Technologies Workshop in Anchorage on Oct. 13.

The first step in designing a mud-line cellar is the acquisition of multibeam sonar images of the seabed, a technique that uses acoustic signals to generate detailed profiles of the sea-floor surface. The sonar images enable gouges to be identified and measured, thus setting parameters for the required mud-line cellar depth, ensuring that the top of the blowout preventer will sit well below the deepest scour.

A typical blowout preventer is 20 feet tall and about 16 feet in diameter, weighing about 500,000 pounds, Teff said.

After the gouge depth measurement is complete, a 20-foot diameter, hydraulically powered rotary bit, with teeth in the form of inward-angled plow blades, carves out a cellar, an operation that typically takes anywhere from two to 10 days to complete. The plow blades direct debris from the operation towards the center of the bit, from where compressed air pushes the debris up through the tubular riser that holds the bit in place on the sea floor, Teff said.

—Alan Bailey