OPRC Level I
Spilled oil properties,
behaviour and fate
Version No.2 - 19.05.2015
Aim
Knowledge of how oil behaves in the marine
environment is essential for mounting effective
response actions
• Physical & Chemical
Properties
• Spreading & Movement
• Weathering of Oil Spills
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Physical & Chemical Properties
– Oils of Concern
Crude oils
Refined products
•Heavy fuel oils
•Gasoline
•Diesel
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Physical & Chemical Properties
– Persistent and Non-Persistent Oils
Persistent
•Many crude oils
•Heavy refined products
Non-Persistent
•Naphta
•Kerosene
•Gasoline
•Diesel
•Vegetable oils
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Physical & Chemical Properties
– Key Physical Properties
Density (specific gravity)
•oil’s ability to float
Viscosity
•how much it flows
•how thick it is
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Physical & Chemical Properties
– Other Physical Properties
• Volatility
• Pour point
• Asphaltene content
• Flash Point
• Surface Tension
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Comparison of Oil Properties
Oil Type
Density g/ml
Viscosity cSt
Distillation
characteristics
% boiling below 200 °C
% boiling above 370 °C
Typical
Crude
0.85 to 0.90
10 to 50
25
Gasoline
0.75
1
Diesel
0.85
1 to 5
0.95 to 0.98
5000 to 10000
1
1
Heavy Fuel
Oil
Water
100
0
20
50
10
65
100
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Pour point
°C
-40 to -50
-20
-5 to15
0
Spreading & Movement –
Spreading of Oil Spills - Facts
• Oil spreads very quickly on
water
• Forms thin layer
• Covers a large area
• High rate of spreading at first
• Rate gradually slows down
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Spreading & Movement –
Spreading of Oil Spills - Factors
Spreading rate depends on:
•Oil properties
•Volume
•Temperature
•Wind velocity
•Waves and current
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Spreading & Movement –
Spreading of Oil Spills - Estimation
• Use spreading tables to predict size of slick
• Must know spill volume and general oil type
• Rapid spreading at first
• Reaches equilibrium - won’t spread more
• Estimate average slick thickness by dividing the volume of
spill by the area of spill
• Rule-of-thumb:
o
90% oil in 10% area
o
10% oil in 90% area
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Spreading & Movement –
Spreading of Oil Spills - Fragmentation
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Spreading & Movement –
Simplified Cross Section of an Oil Spill
Direction of wind
90% of oil
in 10% of
slick area
10% of oil
in 90% of
slick area
Lens shaped
oil layer
water
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Spreading & Movement –
Spreading of Oil Spills - Rule
Time and the spreading
process both detract from
the efficiency of the
response.
Rapid response is vital for
effective results.
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Spreading & Movement –
Movement of Oil Spills - Assessment
• Computer models
• Simple calculations
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Spreading & Movement –
Movement of Oil Spills – Rule of Thumb
Surface current speed and direction modified by 3% of
wind speed and direction
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Weathering of Oil Spills
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Weathering of Oil Spills –
Evaporation Facts
• Changes oil properties
• Reduces spill volume for light oils
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Weathering of Oil Spills –
Evaporation Rates
Evaporation rate is affected by:
•Chemical composition
•Slick thickness
•Temperature
•Wind speed
•Sea state
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Weathering of Oil Spills –
Typical Evaporation Losses
• Light crude oil and light refined products :
o
Up to 30% in 12 hours
o
Up to 50% in 1 day for light oils
• Gasoline up to 100%
• Heavy crude/fuel oil very little
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Weathering of Oil Spills –
Natural Dispersion
Important removal process
for low viscosity oils
Braer
Shetland Isles, UK, 1993
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Weathering of Oil Spills –
Emulsification
• Water-oil (mousse)
• Increase in spill volume
• Large increases in slick
viscosity
Typical emulsions
contain
75 to 90 % water
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Weathering of Oil Spills –
Interaction of spill processes
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Weathering of Oil Spills –
Dissolution
Not relevant in first response
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Weathering of Oil Spills –
Biodegradation
Not relevant in first response
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Weathering of Oil Spills –
Photo-oxidation
• Promoted by Sunlight
• Creation of tar-balls
• Result is water - soluble
compound or increased
viscosity
• Effect on overall
dissipation is minor
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Weathering of Oil Spills –
Sedimentation
• Adhesion of particles or organic matter
• Effects of temperature
• Some heavy refined products with specific
gravity >1 will sink in fresh or brackish water
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