Impacts of Oil Exploration and Drilling on Permafrost

Examining the soil and water cycles of the 1002 region, one cannot ignore the presence of permafrost, or ¡§permanently frozen soil,¡¨ which underlies 80% of Alaska and remains a central issue in the debate about oil drilling. Permafrost has been defined as frozen ground in which a naturally occurring temperature below 0¢X C (32¢X F) has existed for two or more years (A). On the North Slope, permafrost ranges in thickness from about 700 to as much as 2,240 feet thick, and may be as cold as -8° to -10° C.

Permafrost can be either thaw-stable or non thaw-stable, depending on the type and percentage water of the soil it is made of. Permafrosts in more fine-grained soils like loess (silty) tend to thaw, sink, and create thermokarsts more often. Permafrost thaws from heat input, such as global warming or human activity, as well as the clearing of vegetation which insulates the ground.

Permafrost is affected by road dust generated by traffic on unpaved roads; snow melt due to dust deposition can lead to flooding, ponding, and hydrological changes in oil. Continuing oil and gas exploration, development, and production, construction of a natural gas  pipeline, the operation and maintenance of facilities, and other activities requiring road travel would add cumulatively to the volume of road dust generated on unpaved roads (A). Regions of ice which have been wind-dusted are likely to undergo localized melting earlier than the neighboring non-dusted ice (A).

There are three approaches to dealing with the permafrost problem in the construction practice. The first and most obvious is to avoid it entirely. The second is to destroy it by stripping the insulating vegetative cover and allowing it to melt over a period of years. This has the obvious drawback of requiring a considerable period of time to elapse before construction can begin, and even then, it is a good idea to excavate the thawed ground and replace it with coarse material.

The third approach, and one which is becoming more widespread, is to preserve it. This can be accomplished by building on piles to allow cold air to circulate beneath heated structures, by building up the construction site with gravel fill which insulates and protects the permafrost below, or by refrigeration to maintain low ground temperatures. This is done by utilizing thermal piles or freeze tubes, such as those used by the trans-Alaska pipeline. These devices are filled with a non-freezing liquid and act like coffee percolators. They are cooled during the winter months and draw heat from the ground to retard thawing during warm weather (A).

In nearshore areas, ice-bonded permafrost is probably present and must be considered in the design of an offshore pipeline. But nearshore ice-wedge permafrost under shallow water, particularly along a rapidly receding coastline, is even more critical for design. Oil pipelines placed in areas of ice-bonded or ice-wedge permafrost must be heavily insulated to limit thawing of permafrost. The best location for an offshore platform is at water depths of 6.5-65 feet, to minimize ice gouging. Beyond the 6.5 foot water depth the top of the ice-bonded permafrost generally is below the surface of the seabed. Inshore of the 18-foot bottom-depth contour, ice gouging is typically less than 1.6 feet (Y).

Relation of oil drilling, permafrost and vegetation

Permafrost layer restricts the drainage of water through the soil, making it moist in the short summer growing season. It is easily broken by road construction or the seismic explosions used in oil exploration, changing the water drainage patterns of the soil and thus retention of moisture. Melting permafrost has also led to widespread damage of buildings, costly road repairs, and increased maintenance for pipelines and other infrastructure ¡V impacts that will continue to grow in magnitude. Permafrost also stores large amount of ancient carbon and methane; thawing is likely to release some of this stored carbon and methane back into the atmosphere, amplifying the risk of further climate change. The boreal forest will advance northward into present coastal plain tundra, and mixed forest into present boreal forest. Forest fires and insect outbreaks, both of which have increased sharply in recent years, will further increase. If the permafrost thaws, the vegetation will in the long term dries out, altering plant communities and use by wildlife.

It has been observed that in areas where the permafrost thaws, there is a sudden rapid growth of plants, which attract more animals to feed on. However, this is only momentary. Once the permafrost thaws, temporarily there is much water for plants to grow well for like a month or two, but then the water is continuously used up and drained away as there is no layer to prevention drainage now; yet the permafrost, once destroyed, take years to resume. Therefore, a few months after destruction, water will finally be deficient and no plants can grow well even during summer when water has already been used up, drained away but no permafrost exists to trap them for the growing season. This detrimental effect on vegetation is permanent, while the vast growth of plants is just transient.

Reference:
1.    Union of Concerned Scientists (2002). http://www.ucsusa.org/global_environment/archive/page.cfm?pageID=780
2.    Williams, M.; Rastetter, E. Vegetation characteristics and primary productivity along an arctic transect: implication for scaling-up. Journal of Ecology 1999 87: 885-898.