Anchorage Daily News

The most recent wave of oil exploration in the Beaufort and Chukchi seas has hardly left the starting block. But finding a viable and environmentally sound means of extracting product from a field located under icy water miles offshore could make or break a development project.

Early this year the U.S. Minerals Management Service published a 365-page report on Arctic offshore development options. In assessing the various development options, the study researchers reviewed the experience of the Northstar, Oooguruk and PanArctic Drake developments in the Alaska and Canadian Beaufort Sea. The researchers also considered offshore developments off the east coast of Canada, off Russia's Sakhalin Island, in the Caspian Sea and in the Barents Sea.

The researchers recognized that the principal factors affecting the design of Arctic offshore facilities include ice loads; the requirement for a platform or island structure to store sufficient consumable supplies for operation in an isolated location; the availability of an adequate foundation or mooring capability; the capability to protect pipelines and subsea equipment; and the practicality of transporting produced hydrocarbons from the offshore site.

And in the Beaufort and Chukchi seas ice loads are an especially important consideration in designing exploration and production structures, says the report prepared by IMV Projects Atlantic. However, research into ice loads has indicated that these loads are likely to be significantly lower than was assessed a few decades ago.

"At the same time, advancements in structural steel research combined with these more realistic ice-load predictions led to improvements in the economic feasibility of Arctic offshore facilities," the report says.

But massive gravity-based structures sitting on the seafloor remain the most likely option for oil and gas production in the challenging ice conditions of the Beaufort and Chukchi seas. And the study says that in Arctic conditions steel is likely to prove to be a more suitable construction material than concrete.

Depending on factors such as the type of sea ice and the water depth at a specific location, a variety of platform designs is possible for northern seas. Designs range from massive vertical cylinders to more tapered profiles.

The researchers found that in areas of multi-year ice, water depths of about 250 feet would likely become an upper limit for the technical feasibility of installing these structures, but that limit would go down to 200 feet where the seafloor foundation properties are weak.

"There are no known bottom-founded platform design solutions for water depths greater than 330 feet that could be deemed workable or proven for multi-year ice areas," the report says.

In more southerly area where multi-year ice is absent, bottom-founded structures in water depths up to 500 feet might be possible.

JACKET PLATFORMS

The lighter-weight, ice-reinforced jacket platforms like those use in the offshore fields of upper Cook Inlet might be suitable for use in areas of the Bering Sea where there is light first-year ice and water depths are less than 200 feet, the report says.

"(And) developments in jack-up technology and the advancement of ice maintenance programs indicate that the operating range and season of jack-up exploration could potentially be extended in the Bering Sea," the report says.

Grounded ice islands have also been used successfully for exploration drilling in the nearshore waters of the Beaufort Sea, the report says. Research has found that ice islands might work for drilling in water depths up to 30 feet, or perhaps 40 feet. But unstable or unreliable landfast ice would render ice islands infeasible in the Chukchi Sea, the report says.

The use of gravel islands is another possibility in shallow water. They've been used for offshore oil fields in Alaska's Beaufort for decades.

However, because no one has ever used a gravel island in the Chukchi Sea -- where oil companies bid $2.6 billion to acquire leases in federal waters earlier this year -- someone would need to investigate issues relating to dynamic sea ice conditions to determine gravel island feasibility in that region.

FLOATING STRUCTURES

Although various types of floating structures such as drillships and semi-submersible platforms can be used during the summer when the ice is gone in the Arctic outer continental shelf, the only region in which a floating structure might stay on location year round might be the Bering Sea in light ice conditions. A semi-rigid floater concept, with a floating platform moored in place under tension, might operate year-round in first-year ice conditions but would need to be able to disconnect to move away in the event of high ice loads, the report said.

Subsea completions, in which wellheads lie at or below the seafloor and are connected to subsea pipelines, are another possibility.

"Improvements in the area of subsea facilities and processing have been made in recent years in the pursuit of resources in harsh and remote environments," the report says. "As a result of these improvements, fields requiring longer, deeper subsea tiebacks are now becoming much more technically and economically feasible. Gas tiebacks have reached 105 miles and oil tiebacks have reached 40 miles."

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