Fossil fuels = energy from remains of once-living organisms. Fossil fuels are non-renewable resource because rate of use (past 100 -200 years) is much faster than rate of renewal (millions of years). Renewable resources = wind, solar energy, tides, biomass, methane from landfills.
Origin of Fossil Fuels - General
A) Accumulation of abundant organic matter
B) Preservation of organic matter - need to prevent oxidation (keep away from atmosphere)
C) Conversion of organic matter to fossil fuel - involves heating
(50 - 150°C) due to burial for long time (millions of years). > temperature
result in conversion to > grades of fossil fuel.
I) Oil (petroleum) - composed of hydrocarbons (organic chemicals composed of chains of C + H). Hydrocarbons range from long chains (polymers) of C (solid = tar), to smaller C chains (thick viscous lubricating oils to light oils such as gasoline) to single molecules (natural gas = methane = CH4). Heavy oil, light oil, + natural gas represent > grades of petroleum, formed with > temperature.
II) Origin of Oil - derived from remains of plankton (tiny marine plants + animals).
1) Accumulate + preserve plankton in layers of oceanic sediment
(usually mud)
2) Bury organic-rich mud with many overlying layers of sediment. High temperature (50 - 100°C) due to burial converts organic matter to oil (over millions of years). At same time, mud becomes shale - source rock (rock in which oil originally forms) for oil. Shale is impermeable (liquids such as oil flow VERY slowly through it), so little oil can be recovered.
3) Migration of oil from source rock (impermeable) to reservoir rock
(permeable - liquids can flow faster) located in oil trap (where
oil can be extracted by pumping). Oil is very light (buoyant) so
it tends to move upward, eventually reaching Earth's surface where it would
be lost. Need oil trap (configuration of rock layers which act as barrier
to upward migration of oil). Example of oil trap = folded or bent rock
layers with source rock on bottom, then reservoir rock (e.g., sandstone),
+ then impermeable seal rock on top (e.g., shale). Note: oil is not located
in large, underground cavities, but in tiny spaces between mineral grains
(pore space). Formation of oil is very complex, need all of above steps
or else you don't have economic oil deposit.
III) Production of Oil
1) Exploration - seismic reflection profiling - Set off dynamite,
shock waves penetrate into Earth, some are reflected back + recorded; gives
image of rock layers in subsurface to help find oil traps.
2) Drilling - platform with pipes connected to rotating metal drill with diamond bits to cut through rock
3) Pumping - use suction pressure
4) Transport - pipelines, large ocean tankers
5) Refining - chemical facility that changes crude oil into usable forms.
IV) World Supply + Demand of Oil
Where? Middle East
USA has ~3% of world's oil + imports ~half of its oil
How much remains? several decades (< 50 years)
V) Coal - remains of land plants; organic chemicals composed mostly of C (+ O, H, S, + N as impurities); major energy resource of 1800's; bulky, dirty (to handle + burn); major use = burning in power plants to generate electricity.
World Supply + Demand of Coal
Where? USA has abundant coal
How much remains? several centuries
VI) Origin of Coal
Swamp - Begin with prolific plant growth in freshwater swamp. Plants
fall into stagnant water (low in O2 because it is away from
O2 in atmosphere) + is preserved. Burial with overlying rock
layers changes character of plant matter. High temperature + pressure produces
different grades (ranks) of coal: peat (compacted plant debris -
50% C), lignite (brown coal - 70% C), bituminous - (dull,
black coal - 80% C), anthracite (shiny, black coal - 90% C), + graphite
(~pure C). > C content = > heat content.
VII) Production of Coal
Exploration - coal occurs in seams (layers) often near Earth's surface (easier to find than oil); common in Carboniferous-age (Late Paleozoic) rocks.
Two methods of extraction
Strip mines - use large motorized shovels (drag lines); dig down to coal layer, scrape it out + then refill hole.
Underground mines - underground hole + network of tunnels that
follow coal seam; used when coal is located too deep for strip mine to
be economic.