Fossil Fuels

Fossil Fuels

• Remains of ancient organisms

• Accumulated, compacted, modified

• Estimated less than 0.1% of matter incorporated

Fuel-forming Reactions

• Not well understood– Many products– coal, kerogen hard to characterize

• Fragmentations– loss of small molecules: H2O, CO2

• Condensation and Polymerization

Oil

• Most versatile fuel source– Easy to transport– Easy to refine– Many different derivatives– Refined product burns without residue

Forming Oil

• Dead plankton settle to sea floor– Incorporated in mud– Decomposes anoxically

• Becomes kerogen in oil shale

• Water, pressure, heat chemical change– Bitumen, Oil,Gas

Oil Deposits

• Oil seeps to surface destroyed

• Must be trapped underground

• Must be recoverable

Recoverable Oil

• Source rock: organic matter subjected to proper conditions

• Reservoir rock: porous and permeable

• Cap rock: impermeable

Oil from Shale

• Large recoverable deposit in Green River Formation

• Heating oil shale: retorting

• Product similar to crude oil

Coal

• Created from swampy plant residue

• Compacts, decays anaerobically

• Compression and heating “matures” coal

Forming Coal

Coal Rank

Peat

Lignite

Sub-bituminous

Bituminous

Anthracite

Graphite

Low maturity

High maturity

Low %C

High %C

Low energy

High energy

Worldwide Coal

• Mostly from Carboniferous

• Lots of swamps, warm climate

• Later sea-covered– Sulfate-reducing bacteria acted on deposits– Put sulfur compounds in coal– Pollution upon combustion!

Wyoming Coal

• Wyoming arid during Carboniferous

• WY coal is Cretaceous– Low grade– Never subsequently sea-covered– Low-sulfur

US Coal Production

Gas

• Principally CH4, some C2H6

• May include CO2

• Formed in all stages of organic degradation

• Can be associated with coal or oil

Gas Hydrates

• Ice-like complexes of water and methane– water framework with methane in voids

• Stable at low temperatures and high pressures– Found in permafrost, marine sediments

• Estimated to be world’s largest fossil fuel resource