Pipelines and the permafrost

On the morning of 2 March 2006, an oilfield worker was driving through a remote Alaskan wilderness, about 650 miles north of the state's biggest town, Anchorage, to make his routine daily inspection of a section of the Trans-Alaskan Pipeline System that runs from Prudhoe Bay, further north (Map 2). Over the preceding few years he had never noticed anything seriously out of the ordinary, but on this particular occasion he was hit by the unmistakably acrid stench of oil.

Almost immediately, the sheer scale of the leakage became apparent, for around 267,000 gallons of crude had escaped from a tiny crack in the pipeline caused by metal corrosion. Undetected for 5 whole days despite regular checks, this leakage had inflicted a devastating environmental blow, while also hammering the share price of the operator, BP, and edging up the global price of crude oil. 'I can confirm it's the largest spill of crude oil on the North Slope that we have record of', Linda Giguere, from Alaska's Department of Environmental Conservation, told one news agency. Environmentalists from the Alaska Wilderness League also said the spill was 'a catastrophe for the environment' and 'a painful reminder of the reality of unchecked oil and gas development across Alaska's North Slope'.

The prospect of a leaking oil or gas pipeline in the Arctic is a particularly appalling one. In such a remote region, days or even weeks could pass before any leakage is noticed, and even in a short space of time its impact on a wilderness area could be devastating. This is one reason why plans to build pipelines through Alaska, northern Canada and other Arctic regions have proved highly controversial.

Thawing permafrost poses different threats to oil and gas pipelines because the two substances are moved in quite different ways. Oil usually passes through pipelines at a relatively high temperature that reduces its viscosity and therefore makes it easier and quicker to pump. But natural gas is often pushed through pipelines at temperatures below freezing in order to increase its density.

The high temperature of piped oil can cause a serious engineering problem when a pipeline has been built below the ground surface, which is seen as a cheaper and more environmentally friendly option. In this scenario, the pipeline easily warms the surrounding soil, aggravating the effects of thawing permafrost and making the ground much less firm than before. So anything on top of the ground might collapse as a result, while the underground pipeline is at serious risk of being undermined, becoming distorted and eventually cracking.

Engineers are struggling to get round this problem in all sorts of ways. They have tried insulating the pipelines to prevent the warm oil from thawing the surrounding permafrost, but found this to be completely impractical. Another possible solution is to elevate the pipeline, supporting it above the surface on a special foundation that stops it from thawing the ground. This is very costly to undertake, but about half of the Trans-Alaska Pipeline System, which stretches 800 miles from Prudhoe Bay to the ice-free port of Valdez in southern Alaska, has been raised in this way. However, the problem with this approach is that the pipeline still ultimately relies on the permafrost layer for structural support, since it rests on a specially built foundation that is embedded in the soil. If the ground beneath starts to subside then the strain on the pipeline's metal will be considerable.

Experts have devised a way of burying the pipeline while chilling the oil to more or less the same temperature as the permafrost. So before it enters the Norman Wells Pipeline, which runs 550 miles through the western Canadian Arctic from the Northwest Territories to Alberta, the oil is initially chilled by a refrigeration system and then stays at these low temperatures as it makes its journey. This approach is not only just as expensive as the various alternatives but also carries just as many risks because, once again, the pipe trench is still dependent on the structure of the underlying permafrost. In some parts of the Norman Wells link, for example, the permafrost has thawed and as a result the pipe has moved, often much more than anyone expected.

Either way, the environmental challenges in the Arctic region are considerable, and they are likely to be a cause of serious tensions and disputes, mainly between governments, lobby groups and the general public, in the years ahead.

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Part 3 The Contestants

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