The Davis Strait - DCE - Nationalt Center for Miljø og Energi

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11 Impacts from accidental oils spills
Flemming Merkel, David Boertmann, Anders Mosbech (AU), Fernando Ugarte
(GINR), Doris Schiedek, Susse Wegeberg & Kasper Johansen (AU)
11.1 Oil spills
A serious issue of environmental concern from hydrocarbon activities in the
marine Arctic environment is a large oil spill (Skjoldal et al. 2007). The probability
of such an event is low and in general the global trend in amounts of
spilled oil is decreasing (Schmidt-Etkin 2011). But the impacts from a large
spill can be severe and long lasting especially in northern areas.
Several circumstances enhance the potential for severe impacts of a large oil
spill in the assessment area. The Arctic and sub-Arctic conditions reduce the
degradation of oil, prolonging potential effects. The occurrence of ice, at
least in winter, may influence the distribution and fate of oil (see below), and
will also make oil spill response difficult in periods with extensive ice coverage
or otherwise harsh weather conditions.
According to the AMAP oil and gas assessment tankers are the primary potential
spill source (Skjoldal et al. 2007). Another potential source is spills
from a blowout during drilling, which in contrast to tanker spills are continuous
and may last for many days; for example, the Deepwater Horizon
blowout lasted 106 days before it was stopped by relief drilling.
11.1.1 Probability of oil spills
Large oil spills are generally very rare incidents. However, the risk is present
and cannot be eliminated. In relation to oil drilling in the Barents Sea, it has
been calculated that the possibility of a blowout between 10,000 and 50,000
tonnes would happen once every 4,600 years in a small-scale development
scenario and once every 1,700 years in an intensive development scenario
(Anon 2003b). The likelihood of a large oil spill from a tanker ship accident
is estimated to be higher than for an oil spill from a blowout (Anon 2003b).
Drilling in deep waters (between 1000 and 5000 feet ~ 305-1524 m) and ultradeep
waters (> 5000 feet ~ 1524 m) increases the risk for a long-lasting oil
spill, due to the high pressures encountered in the well and due to difficulties
in operating at these depths. It took three months to cap the Macondo
well (Deepwater Horizon spill), partly because of the deep water (1500 m)
(Graham et al. 2011).
11.1.2 The fate and behaviour of spilled oil
Previous experience with spilled oil in the marine environment gained in
other parts of the world shows that fate and behaviour of the oil are highly
variable. Fate and behaviour depend on the physical and chemical properties
of the oil (light oil or heavy oil), how it is released (surface or subsea, instantaneous
or continuous) and on the conditions of the sea into which it is
spilled (temperature, ice, wind and current).