Environmental Statement - Maersk Oil

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6 ‐ 8 Balloch Field Development Environmental Statement Section 6 Accidental Spills output of 19,700 m 3 /day; this is a worst case assumption as the flow rate is expected to decline with time. Shoreline oil modelled outputs There is a possibility of hydrocarbons beaching on Shetland, Orkney, mainland UK, Norway and Denmark following a 90 day subsea release. This is summarised in Figure 6‐3. A maximum of 1,986 tonnes of oil is predicted to reach the coastline, which could represent 9,930 tonnes of emulsion (based on 80 % water content predicted by the weathering analysis). The minimum time to reach shore is 20.7 days. The hydrocarbons reaching the Norwegian coastline are more likely to be in the form of dispersed oil in the water column, rather than a surface slick. The graphs in Figure 6‐3 show the amount of oil beached and the time it takes to beach, as well as the cumulative percentage of scenarios in which this happens. Water column and sediment modelled outputs The water column and sediment concentration outputs are summarised in Figure 6‐4. Water column and sediment concentrations are not expected to exceed 50 ppb beyond approximately 450 km from the release, except very locally around patches of surface oil. Sediment concentrations of around 1170 mg/kg (peak) and 200 mg/kg are predicted. Water column levels below 50 ppb are not expected to have a significant acute toxic effect while the sediment levels are higher than the 50mg/kg OSPAR recommendation for oil in sediment. Fate of oil and fixed wind analysis The fate of the hydrocarbons associated with a 90 day subsea blowout is shown in Figure 6‐5. This shows that 30 days after the release has been controlled, approximately 50 % has decayed, 10 % has evaporated, 30 % is in the sediment and less than 15 % is dispersed in the water column. Fixed wind analyses predict that in the presence of 30 knot offshore winds (east to west), hydrocarbons will cross the UK ‐ Norwegian median line in 3.5 days and in 6.5 days in the presence of 30 knot onshore winds (west to east). The surface slick would still cross the UK‐Norwegian median line in the onshore wind scenario, albeit in a longer time period, as a result of the prevailing water currents. The outputs are summarised in Figure 6‐5. Typical manifestation of oil during release Figure 6‐6 presents instantaneous snapshots of the appearance of the surface slick and water column plume. The surface example is chosen to represent a period of relatively calm winds that allow oil to accumulate on the surface, which in this scenario occur on day 84, i.e. it is a relatively pessimistic prediction as to the extent of the surface slick. The water column example is chosen as being at the end of the release period, after which concentrations would be expected to decline. The cross‐section image shows the oil accumulating in the water column above the release site on the seabed. Oil does not appear in the entire water column as it moves rapidly up towards the surface after release from the well, where it then accumulates.
Balloch Field Development Environmental Statement Section 6 Accidental Spills Figure 6‐2 Surface slick summary outputs for a well blowout at subsea. Volume released m 3 19,700 m 3 Probability of visible surface oil at any time Oil type SNORRE B Release position 1,773,000 Release duration Rate of release / day Median lines crossed % likelihood Mass balance (tonnes) 62°00'N 60°00'N 58°00'N 56°00'N 40000 30000 20000 10000 0 5°00'W 5°00'W 200 km Blowout ‐ subsea release 0°00'E 0°00'E 5°00'E 5°00'E Entire at seabed Norway Faeroes Denmark Germany Neth's 100% 0% 50% 1 ‐ 10 % 1 ‐ 10 % Typical mass of oil on surface over time 10°00'E Statistical Map: Surface: Probability of contamination above threshold (0.000 mm) [%] 10°00'E 90 days 0 20 40 60 80 100 120 140 Time (days) Surface 62°00'N 60°00'N 58°00'N 56°00'N 6 ‐ 9
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Environmental Statement Balloch Fie
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Balloch Field Development Environme
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B ‐ 2 Halocarbon release during e
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B ‐ 4 Lube and hydraulic oil spil
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Discharges to Sea Discharge from pi
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Production Phase Environmental Aspe
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B ‐ 10 Drainage water Discharge o
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Physical presence Oil and gas infra
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Major accidental events Other envir
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Environmental Statement - Maersk Oil

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