Chapter 17: Fossil Fuels and the
Environment
Fossil Fuels
• Fossil fuels are forms of stored solar energy
– Plants convert solar energy to chemical energy
through photosynthesis
– Incomplete decomposed organic matter then
covered up
– Converted to oil, natural gas, and coal
• Provide 90% of energy consumed
Crude Oil and Natural Gas
• Most geologist accept the hypothesis that
these derived from organic matter
– Buried in what are known as depositional basins
• Oil and gas primarily found along plate
boundaries
– Exceptions to this include Texas, Gulf of Mexico
and the North Sea
Crude Oil and Natural Gas
• Source rock is fine grained, organic-rich
sediment
– At a depth at least 500 m
– Subjected to increased heat and pressure that
initiates the chemical transformation
– Elevated pressure causes sediment to be
compressed
– This initiates upward migration to lower-pressure
reservoir rock
Crude Oil and Natural Gas
• Reservoir rock is coarser grained and relatively
porous
– E.g. sandstone and porous limestone
• Trap
– Natural upward migration of the oil and gas is
interrupted or blocked
– Rock that helps form a trap known as cap rock,
often shale
Petroleum Production
• Primary production
– Involves simply pumping the oil from wells
– Recovers only 25% of petroleum in reservoir
• Enhanced recovery
– Increase the amount recovered to about 60%
– Steam, water, or chemicals injected into the
reservoir to push oil towards wells
Petroleum Production
• Next to water, oil is the most abundant
fluid in the upper crust
– Concentrated in a few fields
– Proven oil reserves are the part of the total
resource that has been identified and can be
extracted now at a profit
• Domination of energy use in NA but not
reserves.
– Leads to trade imbalance
Oil in the Twenty-First Century
• Recent estimates of proven oil reserves
suggest that oil and natural gas will last only a
few decades.
• When will we reach peak production?
– Likely to be between 2020-2050
– Will have to adjust to potential changes in lifestyle
and economies in a post-petroleum era
Oil in the Twenty-First Century
– For every three barrels of oil we consume, we are
finding only one barrel.
– In the US production of oil as we know it now will
end by 2090. World production by 2100.
Oil in the Twenty-First Century
• Before shortages we need to planning and
appropriate action to avoid
– Military confrontation
– Food shortages
– Social disruption
• Need to develop alternative energy sources
– Solar energy
– Wind power
– Nuclear power
Natural Gas
• Only begun to utilize this resource
– Transported by pipelines
• Worldwide estimates of recoverable gas
will last about 70 years.
– In US about 30 years
• Considered a clean fuel
– Produces fewer pollutants than burning oil or
coal
– Could be a transition fuel to alternative energy
Coal-Bed Methane
• The process of coal formation also produces a
lot of methane that is stored within coal
– Estimated amount is about five-year supply
• Promising energy source however there are
several environmental concerns
– 1. Disposal of large volumes of salty water
– 2. Migration of methane, which may contaminate
surrounding areas
Coal-Bed Methane
• Environmental benefits
– Produces a lot less carbon dioxide than does
burning coal or petroleum.
– Reduces the amount of methane released into the
atmosphere
Methane Hydrates
• Beneath the seafloor there exist deposits
known as methane hydrates
– White, ice like compound made up of molecules
of methane gas molecular “cages” of frozen water
– Forms as a result of microbial decomposition on
the sea floor and then trapped in ice
– Also found on land in permafrost
Methane Hydrates
• Found in ocean where deep, cold seawater
provides high pressure and low temperatures.
– Not stable at lower pressure and warmer temps.
• Documented cases of releases seen off coast
of Norway
• Potential energy source but currently no way
to mine or transport the gas
Environmental Effects of Oil and
Natural Gas
• Recovery, refining, and use of oil and natural
gas cause well documented environmental
problems
– Air and water pollution, acid rain, and global
warming
Recovery
• Possible environmental impacts on land include:
– Use of land to construct pads for wells, pipelines, and
storage tanks and to build a network of roads and other
production facilities.
– Pollution of surface waters and groundwater from: leaks
from broken pipes or tanks containing oil or other
chemicals and salty water (brine) that is brought to the
surface in large volumes with the oil.
Recovery
– Accidental release of air pollutants, such as
hydrocarbons and hydrogen sulfide (a toxic gas).
– Land subsidence (sinking) as oil and gas are
withdrawn.
– Loss or disruption of and damage to fragile
ecosystems, such as wetlands or other unique
landscapes.
Recovery
• Environmental impacts associated w/ oil production
in marine environment:
– Oil seepage into the sea from normal operations or large
spills from accidents.
– Release of drilling muds containing heavy metals, such as
barium, that may be toxic to marine life.
– Aesthetic degradation from the presence of offshore oil
drilling platforms, which some people think are unsightly.
Refining
• At refineries, crude oil is heated so that its
components can be separated and collected
– Fractional distillation
• Accidental spills and slow leaks
– Over years large amount of hydrocarbons
released, polluting soil and ground water
• Variety of chemicals used in the industrial
process which have the potential to pollute.
Delivery and Use
• Crude oil mostly transported on land by
pipelines and across the ocean in tankers
– Both have danger of oil spill
• Air pollution most serious impact associated
with use (burning)
– Contributes to urban smog
Coal
• Partially decomposed vegetation, when buried
in a sedimentary environment, may be slowly
transformed into the solid, brittle,
carbonaceous rock.
– Most abundant fossil fuel
– At current consumption rate could last 250 years
Coal
• Classified according to its energy and sulfur content
–
–
–
–
Anthracite
Bituminous
Subbituminous
Lignite
• Energy content greatest in anthracite and lowest in
lignite
• Lower sulfur coal emits less sulfur dioxide
Coal Mining and the Environment
• In US thousands of sq miles disturbed by coal
mining
– Only about half reclaimed
• The process of restoring and improving disturbed land,
often by reforming the surface and replanting
vegetation.
Strip Mining
• A surface process in which overlying layers of
soil and rock is stripped off to reach the coal.
– Over half of the coal in US mined this way
• One serious problem is acid mine drainage
– The drainage of acidic water from mine sites
– Happens in eastern US where there is abundant
rain fall
Strip Mining
• Acid mine drainage occurs where surface
water infiltrates spoil banks
– Water reacts with sulfide minerals to produce
sulfuric acid.
– The acid then pollutes streams and groundwater
Strip Mining
• In arid and semiarid regions the land may be
more sensitive to activities related to mining
– Exploration and road building
– Soils thin and water scarce
• Makes reclamation more difficult
• Reclamation can minimize damage
– Laws vary by site
Strip Mining
• Appalachian Mountain’s of West Virginia
– Technique known as “mountaintop removal”
– Strip-mining levels tops of mountains and fills
valleys w/ mining waste
– Flood hazard increases as valleys filled w/ mine
waste and toxic waste water is stored behind coal
waste sludge dams
– Also produces voluminous amounts of coal dust
Strip Mining
• Surface Mining Control Act of 1977
– US government has required that mined land
restored to support pre-mining use
– Prohibit mining on prime ag land
– Reclamation includes
• Disposing of wastes
• Contouring the land
• Replanting vegetation
Underground Mining
• Accounts for 40% of coal mined in the US
• Some of the environmental problems:
– Acid mine drainage from the mines and waste
piles has polluted thousands of kilometers of
streams.
– Land subsidence can occur over mines.
– Coal fires in underground mines may be either
naturally caused or deliberately set.
Transport of Coal
• Transporting coal from mining areas to large
population centers where energy is needed.
– Significant environmental issue
– Freight trains and slurring pipelines have been
used
The Future of Coal
• Burning of coal
– produces 60% of electricity used and
– 25% of total energy consumed in US
• Coal 90% of our energy reserves
• However coal power plants emit
– 70% of sulfur dioxide
– 30% of nitrogen oxides
– 35% of carbon dioxide
The Future of Coal
• Clean Air Amendments of 1990 mandate reducing
these emissions.
• Option for cleaner coal include:
– Chemical and/or physical cleaning of coal prior to
combustion.
– New boiler designs that permit lower temp of
combustion.
– Injection of material rich in calcium carbonate into the
gases following burning.
• Scrubbers-removes sulfur dioxides
The Future of Coal
– Conversion of coal at power plants into gas before
burning.
– Convert coal to oil.
– Consumer education about energy conservation
and efficiency to reduce the demand for energy.
– Development of zero emissions coal-burning
electric power plants
The Future of Coal
• As oil and gas reserves dry up more pressure put
on coal.
• Increased use of coal will have significant
environmental impact.
– More land strip mined.
– Burning coal produces large amounts of air pollutants
– Handling of large quantities of coal through all stages
has potentially adverse environmental effects.
• include aesthetic degradation, noise, dust, and release of
harmful or toxic trace elements into the water, soil, and air.
Allowance Trading
• EPA grants utility companies tradable
allowances for polluting
– 1 allowance good for 1 ton of sulfur dioxide
– Could then be traded and sold by brokers
– Idea is to reduced overall pollution through
economic market forces
Oil shale
• Fine grained sedimentary rock containing
organic matter (kerogen).
– When heated to 500oC oil shale yields oil
– Destructive distillation
– The oil from shale called synfuel
Tar Sands
• Sedimentary rocks or sands impregnated with
tar oil, asphalt, or bitumen.
– Recovered by mining the sands and then washing
the oil out with hot water.
– Most in Alberta, Canada
• Strip mined
– Similar problem as w/ shale, greater volume
Oil shale
• Recovery done both surface and subsurface
– Disposal of waste a problem because shale must
be retorted
– Volume of waste 20-30% greater than original
volume.
– Despite this oil shale may developed as oil prices
rise.