Environmental Statement - Maersk Oil

Balloch Field Development Environmental Statement
Section 6 Accidental Spills
6.4.4. CONCLUSIONS OF MODELLING
Uncontrolled blowout scenario 1: Subsea release
The probability of a surface spill crossing into the European countries waters are as follows:
Norwegian (100 %), Danish (50 %), German (1 ‐ 10 %) and Dutch (1 ‐ 10%).
The probabilities of oil reaching the following shorelines are as follows: Shetland (1 ‐ 10 %),
Orkney (1 – 10 %), UK mainland (1 ‐ 10 %) and Norway (30 ‐ 40 %).
Minimum time to beach 20.7 days.
Maximum mass of oil beached 1,986 tonnes.
Maximum emulsion beached 9,930 tonnes.
Sediment concentration average 200 mg/kg.
In an offshore wind the surface slick could cross the UK ‐ Norwegian median line in 3.5 days,
but 6.5 days in an offshore wind.
Uncontrolled blowout scenario 2: Surface release followed by subsea release
The probability of a surface spill crossing into the European countries waters are as follows:
Norwegian (100 %), Danish (60 ‐ 70 %), German (1 ‐ 10 %) and Dutch (1 ‐ 10%).
The probabilities of oil reaching the following shorelines are as follows: Shetland (1 ‐ 10 %),
Orkney (1 ‐ 10 %), UK mainland (1 ‐ 10 %), Norway (100 %) and Denmark (30 ‐ 40 %).
Minimum time to beach 11.8 days.
Maximum mass of oil beached 3,285 tonnes.
Maximum emulsion beached 16,425 tonnes.
Sediment concentration average 30 mg/kg.
In an offshore wind the surface slick could cross the UK‐Norwegian median line in 1.1 days,
but 9 days in an offshore wind.
Summary of blowout scenarios
In the event of a blowout it is likely that oil will cross into Norwegian waters, with a moderate/high
probability of oil entering into Danish waters and a low probability of oil entering into German and
Dutch waters. There is a marginally greater probability of oil entering into Danish waters in the
surface blowout scenario. In both scenarios there is a low probability of oil beaching anywhere in the
UK, although there appears to be a greater probability of oil beaching in Norway and Denmark for the
surface release scenario.
The surface blowout scenario would result in a shorter duration for an oil spill to reach the shore
(11.8 days) compared to the 20.7 days for the subsurface release. The surface blowout is expected to
result in a greater maximum mass of oil beached (3,385 tonnes), in comparison to the subsurface
blowout (1,986 tonnes).
A subsea blowout could cause elevated hydrocarbon levels in the sediments with typical
concentrations of 200 mg/kg; this is far greater than the 30mg/kg that is expected for the surface
blowout. The time taken to cross the UK‐Norway median line is shorter for the surface blowout spill.
Instantaneous Release of the Diesel Inventory from the Drill Rig.
The loss of the diesel inventory does not result in a large or significant impact:
The probability of a surface spill crossing into Norwegian waters is low (1 ‐ 10 %);
Diesel will not reach any European coastline;
The typical sediment would be 2 mg/kg;
In an offshore and onshore wind the surface slick is not expected to cross the UK‐Norwegian
median line.
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