Geology Reference
In-Depth Information
Figure 14.13.
Conceptual illustration of the freezing and thawing effects of a buried, chilled gas
pipeline crossing from unfrozen to frozen terrain, and vice versa, in an area where permafrost was
discontinuous. Modifi ed from Nixon (1990).
increasingly, Eastern Europe. A summary of the operating practices is given by Seligman
(2000), who concludes that most problems can be mitigated, but not eliminated, by strict
regulation (cooling) of gas temperatures from the moment a pipeline begins to operate.
For example, in the early 1970s, there were no compressor stations or gas processing plants
along the pipeline routes. As a result, large sections of trunk gas pipeline transmitted cool
gas (below 0 °C) that promoted frost jacking. Subsequently, in the early 1980s, the intro-
duction of multiple compressor stations together with inadequate gas cooling resulted in
thawing of ground and creation of freeze-thaw thermal regimes around the pipe. Thaw-
related displacement of the pipes followed together with upward fl otation of buoyant,
poorly-ballasted pipes in soils that had lost their load-bearing capacity. In some localities,
the pipelines that had fl oated upwards became exposed at the surface to extreme fl uctua-
tions in seasonal temperatures, chilling the gas in winter and warming it in summer. The
fi nal result was that many pipelines now experience severe frost jacking and an unaccept-
able build-up of stresses in pipe steel. It is clear that the transmission of chilled gas in a
safe and environmentally sound manner has still to be achieved.
One can be reasonably optimistic that solutions to these problems will be found. For
example, in North America, several companies have undertaken natural-scale experi-
ments that aim to understand the thermal regime around buried refrigerated pipelines.
Much information is proprietary but it does appear that the magnitudes of heave, frost-
penetration depths, and thaw settlement can be predicted at engineering levels of accuracy
(Nixon, 1990). Therefore, regulatory issues, market demand, and world energy supply will
largely determine the construction of new pipelines for oil and gas in both North America
and Siberia. What is clear is that a thorough and in-depth understanding of the perma-
frost-terrain-vegetation relationship is required for modern resource development in
northern regions. Today, most enlightened companies and regulatory agencies maintain
“environmental” personnel and departments.
