Ice management key to E&P in arctic regions

Dev George
Managing Editor

• Ice management key to E&P in arctic regions. [26,143]
  
• Iceberg Alley. [11,516]

On April 14, 1912, while on its maiden voyage across the North Atlantic from England to the United States, the luxury liner Titanic struck an iceberg which ripped open its hull and sank on the Newfoundland Grand Banks, just 300 miles south of the site of Canada's huge Hibernia project and the other major field developments of Terra Nova, Ben Nevis, and Whiterose. The Canadian oil and gas province lies precisely in the center of North America's primary iceberg drift pattern, commonly called "Iceberg Alley".

The vast majority of the North Atlantic's largest icebergs originate in Greenland, where they break off the enormous glaciers that cover the island. Others are formed when they break away from the arctic ice pack covering the Arctic Ocean. Ocean currents carry these mountains of mostly submerged ice from their origins along the coast of Greenland and up around Baffin Bay, then down through the Labrador Sea before crossing the Grand Banks to eventually melt in the warm Gulf Stream currents.

Elsewhere in the Northern Hemisphere, icebergs calve from the arctic ice cap to drift into the Barents and Norwegian Seas as well as the North Pacific. Even today, despite radar and air patrols, these floating ice islands have posed a hazard to shipping that has caused all but the most foolhardy to avoid their pathways and essentially prevented any meaningful development of oil and gas discovered in areas where bergs predominate.

Two precedent-setting developments have, however, begun to defy the icebergs: Canada's Grand Banks projects and Russia's Sakhalin Island developments. Neither are in harm's way of the gigantic icebergs the size of a block of office buildings, being in relatively shallow waters where such killers simply cannot go. Both, however, still lie in areas considered high risk for the damage much small bergs can wreak.

In a recent interview with Henk van Zante, Construction General Manager -Topsides and Gravity Base Structure of Canada's Hibernia project, he stated that if he had it to do over again, he wouldn't have used the enormous iceberg-shielding Gravity Base Structure that is characteristic of the Hibernia Platform. Rather, he would go with a subsea system tied to one or more FPSOs, as will be the manner in which the other Grand Banks projects will be developed. The alternative would, he said, save a great deal of money and still have approximately the same protection from drifting icebergs and pack ice.

"With icebergs, the rule is simple," he said. "You either get out of the way or you get the iceberg to go around you, otherwise you must withstand the force."

To do that, Canada's Memorial University in St. John's, Newfoundland, has led the way in developing ice management strategy and technology that is being applied not only in the Canadian aquatory, but elsewhere. In collaboration with the Faculty of Engineering and Applied Science, the Centre for Cold Ocean Resources Engineering, and the Institute of Marine dynamics, its Ocean Engineering Research Centre's research project, led by Dr. Ian Jordaan, has revealed considerable information on ice/structure interaction and ice mechanics that is being put to use worldwide:

• Structures can be designed to withstand the force of a floating iceberg, witness Hibernia's Gravity Base Structure.
• A less reinforced structure could be designed to save money without compromising safety.
• The number of icebergs in a given area can be determined and the probability of a collision predicted to a considerable degree of accuracy.

Based on the realization that a structure could be built that could withstand the force of a floating iceberg, Hibernia's GBS-centered platform was conceived, but, as Henk van Zante said, with today's knowledge of alternative development possibilities, it is unlikely another such massive construction will be built. In Canada's aquatory, it is also unlikely that a less-reinforced structure will be built in the foreseeable future, certainly not for Grand Banks developments. (It is quite possible, however, that the large hydrocarbon reserves of the Labrador Sea may require such structures, thus the research continues.)

Essentially, as a result of Memorial Univer sity's research, an ice management strategy has been put in place to deal with both icebergs and pack ice on the Grand Banks to prevent either from endangering the oil and gas exploration and production operations that are currently ongoing.

Odds of a large iceberg threatening the Hibernia platform are quite low, but the GBS is capable of withstanding the impact of a million-ton iceberg (expected once in 500 years) with no damage and a six million ton iceberg (expected once in 10,000 years) with repairable damage. Large icebergs should simply run aground before reaching Hibernia, however, which stands in 80 meters of water. Nevertheless, any iceberg that comes within two km of the platform can cause considerable damage to Hibernia's Offshore Loading System (OLS), a complex of oil transmission pipelines on the ocean floor. Thus, despite its somewhat protected location, Hibernia has an ice management program in place that will either remove the iceberg or deflect it into a different trajectory so that it will bypass the platform and OLS and no longer present a risk.

At the core of this strategy is the gathering of information about approaching icebergs by the International Ice Patrol of the US Coast Guard and the Canadian Ice Service of Environment Canada, both of which provide air surveillance. This combined with satellite and Radarsat data and data collected by Hibernia's own radar system, allow iceberg (and iceflow) tracking to be prepared for an emergency response. Additionally, platform support vessels equipped with side scan sonar are able to sail alongside a potentially threatening iceberg and record a detailed profile of it to measure its draught and determine whether it could endanger the ocean bottom OLS.

Ice management services for the Grand Banks developments are being provided by Seaborne Information Technologies, a St. John's-based contractor, which is providing weather forecasting, ice management, and physical and environmental data management. The company, in cooperation with Hibernia's fleet of service vessels, is able not only to monitor the movement of potentially harmful icebergs, but to tow them or give them a push into a different trajectory so that their drift will safely bypass exploration and production operations.

Over the years, numerous methods have been tried for safely removing or towing icebergs, but experiments during Hibernia's development have produced more efficient means of accomplishing the avoidance of operations. Bergs were drilled to anchor tows, they were blown up, prop-washed, bumped and pushed, but the best approach appears to be essentially lassoing the giants with long cables and then towing them.

Ice & Sakhalin Island

Russia is confronted not only with icebergs and drifting ice floes in its central Barents Sea region, but with towering ice ridges caused by the buckling of frozen seas that can occur anywhere in the Kara Sea and, more importantly these days, the Sea of Okhotsk, where the development of Sakhalin Island's offshore province is underway. There, ice ridges can rise as high as 35 meters. Icebergs on the surface of the seas are a problem only when melting occurs and the sheet ice breaks into bergs. Because the sea can freeze solid, however, scourging of the seafloor to plowed depths of up to 20 meters is possible, essentially preventing any ocean bottom pipeline network such as will be employed in Eastern Canada. Instead, detachable FPSOs with rapidly removable flowlines will likely be the method of transmitting oil from Sakhalin's new fields.

Platforms for the Sakhalin region, however, may eventually go the way of Hibernia, unless ultradeep subsea production systems can be devised that could withstand the scourging of the moving ice. At present, several designs are being considered, including narrow conical structures and ice-strengthened jacket-mounted platforms incorporating layered stainless steel and plate steel to handle the ice loads (up to two meters thickness a year) and the structural stress caused by ice abrasion.

Copyright 1997 Oil & Gas Journal. All Rights Reserved.