Understanding Crude Oil and Managing Spills
Understanding Crude Oil: Formation and Characteristics
Oil is a natural liquid fuel, comprising a complex mixture of hydrocarbons. Its composition is highly variable from one reservoir to another. It is an oily, blackish-brown liquid, less dense than water and insoluble in it.
Oil is a fossil fuel, formed from the processing by the action of certain bacteria on large masses of plankton. This process took place in the absence of air and under layers of sediment in marine basins near the coast. Because of its low density and high mobility, oil can flow horizontally and vertically to reach a location where it is stabilized. It is often associated with saltwater and gases.
Properties of Crude Oil
Crude oil possesses several distinct properties:
- Has a liquid, oily consistency.
- Ranges in color from brownish to black.
- Insoluble in water.
- Less dense than water.
- Is a fuel.
- Its boiling point varies for each of its components.
Understanding Oil Spills
An oil spill is the release of petroleum hydrocarbons into the environment, especially the marine ecosystem, due to an accident or malpractice. Catastrophic oil spills often result from:
- A blowout.
- The rupture of a pipeline.
- The collision or grounding of a tanker or barge.
- Improper tank washing procedures.
How Oil Slicks Spread
An oil spill spreads over an area, forming an extensive layer. For instance, it has been observed that 1 m3 of oil can form a slick with a diameter of 100 m and a thickness of 0.1 mm in just half an hour.
Sources and Volumes of Marine Oil Spills
Historical data on oil spilled at sea (in tonnes):
| Year | Tonnes Spilled |
|---|---|
| 1973 | 6,110,000 |
| 1979 | 4,670,000 |
| 1981 | 3,570,000 |
| 1983 | 3,200,000 |
| 1985-1989 | 2,400,000 |
Sources of oil dumping at sea include:
- Natural causes: 10%
- Land-based sources: 64% (of which 15-30% is from air pollution)
- Tanker operations: 7%
- Other vessels: 5%
- Accidents (oil holdings/other vessels): 2%
- Other unspecified sources: 12%
Case Study: The 1991 Persian Gulf Oil Spill
In February 1991, one of the worst oil spills occurred in the Persian Gulf during the war between Iraq and a coalition of countries led by the United States. In a deliberate act of environmental terrorism ordered by Saddam Hussein, an estimated 525 million gallons of crude oil were released from the Sea Island oil terminal in Kuwait into the Persian Gulf. This volume was equivalent to 1.8 times the oil spilled in the Castillo de Bellver tanker accident and 13 times the volume from the Exxon Valdez tanker crash.
The Persian Gulf is particularly vulnerable to pollution because it is shallow (averaging 34 meters) and is almost closed. It is estimated that cleaning up the Persian Gulf will require 200 years.
Environmental and Economic Impacts of Oil Spills
The effects of oil on marine ecosystems depend on factors such as the type of oil (crude or refined), quantity, distance from the contaminated site to the beach, season, weather conditions, average water temperature, and ocean currents.
Key impacts include:
- Obstructing the passage of sunlight, hindering photosynthesis for phytoplankton.
- Covering the feathers of birds (especially diving birds) and the skin of marine mammals like seals and sea otters.
- Disrupting livelihoods, leaving thousands of fishermen and shellfish harvesters out of work. They also require significant financial efforts from institutions and authorities for cleanup and restoration.
Oil Spill Contingency Planning
Effective contingency plans should include the readiness of response teams, regular training exercises, and spill modeling.
Oil Spill Cleanup Techniques
Various methods are employed for oil spill cleanup:
Containment and Collection
Oil spills are surrounded by barriers and recovered by skimmers. Oil and water can then be separated by:
- Centrifugation
- Suction pumps
- Adherence to drums/belts
- Absorbent fibers
Dispersants
These are chemicals, similar to detergents, that break oil into small droplets (an emulsion). This process helps dilute the oil and allows it to mix with water, potentially reducing its immediate surface impact and accelerating natural degradation.
Incineration
Burning spilled oil can be an effective way to remove it. In optimal circumstances, this method can eliminate up to 95% of the discharge.
Biodegradation
In nature, microorganisms (primarily bacteria and fungi) feed on hydrocarbons, breaking them down into less harmful substances.
Shoreline Cleanup
Methods sometimes include using jets of pressurized hot water to dislodge oil from coastlines, moving it back into the water for collection or further treatment.