Oil chemistry

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petroleum_compounds energy.usgs.gov

What is Oil?

Petroleum, or crude oil, consists of a mixture of several different chemical compounds. The most common type of compounds in crude oil are hydrocarbons, called so because they consist primarily of carbon (the grey molecules in the diagram to the right) and hydrogen (the blue molecules).

Hydrocarbons are what make petroleum combustible.  Petroleum can come in a variety of different colors and viscosities (thickness of a liquid) depending on the geographical location that it is found. The different physical characteristics of petroleum are a result of changes in the relative percentages of each type of hydrocarbons found in oil from different regions.

Chromatogram (2)

This is a chromatagram that is a result of an analysis of oil using 2D gas chromatoraphy. Each peak corresponds with a different chemical compound found within the oil; these graphs help researchers create fingerprints.

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The unique combination of these chemicals allow scientists to identify “fingerprints” of different types of oil.

Scientists use instruments like gas chromatography mass spectrometers to create chromatograms like the one to the left. Each type of oil will have a different chromatogram or fingerprint. The fingerprint of the oil will also change as it is exposed to weathering effects like light and bacterial degradation. On aspect of our research is to analyze how the oil degrades in the environment.

So what happens when there is an oil spill within the marine environment?

Pie Chart-Monica

An estimation of what happened to the 200 million gallons of spilled oil from the Deepwater Horizon disaster. Data from Lehr, 2014. (Florida Sea Grant/Anna Hinkeldey)

  • Some of the oil from the Deepwater Horizon blowout rose to the surface where emergency responders employed various methods such as controlled burns and skimmers (as seen in the above image) to contain and remove it. A larger portion was recovered directly at the wellhead.
  • Approximately 1.84 million gallons of a commercial grade dispersant called Corexit was used to break the oil up into smaller droplets (called micelles) that could be dispersed into the water column.
  • It is estimated that approximately 10-20% of the oil was dispersed chemically.
  • Additionally, 12-13% of the oil is estimated to have been naturally dispersed by the physical mixing action of currents and waves.
  • About 11-30% is still unaccounted for.
  • About 20-25% of the oil either evaporated when it reached the surface, or dissolved within the water

The oil that is dispersed either chemically (called the Chemically Enhanced Water Accommodated Fraction of Oil, or CEWAF) or naturally (called the Water Accommodated Fraction of Oil, or WAF) becomes more available for bacteria and other microbes to digest. ADDOMEx scientists are studying how the dispersed and dissolved fractions of the oil impact and are impacted by the microbial communities in the Gulf. Microbes are particularly talented at breaking down the hydrocarbons in spilled oil in order to use them as a food source. Watch this video produced by Scientific American to learn more about how microbes can help clean up oil spills.