Chapter 18: 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

• Argument that we are head toward a potential crisis– We are approaching the time when

approximately 50% of the total crude oil available from transitional oil fields will have been consumed.

– Proven reserves are about 1.2 trillion barrels. World consumption is quickly using what is left.

Oil in the Twenty-First Century

– For every three barrels of oil we consume, we are finding only one barrel.

– Forecasts that predict a decline in production of oil are based on many assumptions but most expert agree it is coming in the next few decades.

– 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.