Environmental Statement - Maersk Oil

Balloch Field Development Environmental Statement
6.4.3. SCENARIO 3: INSTANTANEOUS RELEASE OF THE DIESEL INVENTORY FROM THE DRILL RIG.
A worst case diesel inventory loss of 8,642 bbls over a one hour period was modelled.
Surface oil modelled outputs
6 ‐ 20
Section 6 Accidental Spills
In general, the diesel from the surface release travels in every direction from the source of the
discharge. Norwegian waters are at low risk (1 ‐ 10 % probability) of a visible surface spill. No other
countries are at risk of a surface spill entering their waters. The outputs are summarised in Figure
6‐12.
Shoreline modelled outputs
No European shorelines are at risk from the diesel spill.
Water column and sediment modelled outputs
Following a loss of diesel inventory from the drill rig, water column concentrations are not expected
to exceed 50 ppb beyond approximately 35 km from the release, except very locally around patches
of surface oil.
Sediment concentrations of around 3 mg/kg (peak) and 2 mg/kg are predicted in small, isolated areas,
which could be higher locally. This average value is considerably below the 50 mg/kg OSPAR
recommendation for oil in sediment.
Fate of oil and fixed wind analysis
The fate of the diesel associated with loss of inventory from the drilling rig is shown in Figure 6‐13.
This shows that after 30 days approximately 45 % has decayed, 45 % has evaporated and the
remaining 10% is in the sediment. Evaporation and decay are the main factors at work reducing
diesel in the environment. At the end of the simulations, a small percent of the oil is still present in
the water column, dispersed over a wide area.
Fixed wind analyses predict that in the presence of 30 knot offshore and onshore winds,
hydrocarbons will not cross the median line. The outputs are summarised in Figure 6‐13.