Op ch14 lecture_earth3, solar energy

Chapter 14
Squeezing Power from a Stone:
Energy Resources

LECTURE OUTLINE

earth

Portrait of a Planet

Third Edition
©2008 W. W. Norton & Company, Inc.
Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak

Chapter 14: Squeezing Power from a Stone: Energy Resources

Energy Resources

Prepared by

Ronald Parker
Earlham College Department of Geosciences
Richmond, Indiana

Energy Resources
Energy is the capacity to do work.
 An energy resource is matter that can…


Produce heat.
 Power muscles.
 Generate electricity
 Move machinery.


In usable form, an energy resource is called a fuel.
 Energy stored in chemical bonds fuels biotic life.
 Many energy resources are geological materials.




Energy
Human energy consumption has grown steadily.
 Early humans had modest energy requirements.


Food.
 Fuel for fires.




We consume 110x as much.
Food for livestock.
 Agriculture.
 Transportation.
 Mining.
 Manufacturing.
 Industry.




Industrial societies depend mostly on fossil fuels.



Sources of Energy


There are 5 fundamental sources of energy.
Nuclear fusion in the Sun.
 The pull of gravity.
 Nuclear fission reactions.
 Energy in the interior of the Earth.
 Energy stored in chemical bonds.




Sources of Energy


Energy directly from the Sun’s nuclear fusion reactor.
Heat and light radiate outward from the Sun.
 A tiny portion of the solar output strikes Earth.
 Direct solar energy can be used by humans.


Conversion into electricity by photovoltaic cells.
Conversion into heat.


Controlled fusion is currently beyond human technology.



Sources of Energy


Energy directly from gravity.
Gravitational pull of the Moon on the Earth causes tides.
 Tidal flow can be harnessed to drive turbines.




Sources of Energy


Energy involving both solar energy and gravity.
Solar radiation heats air and evaporates water.
 Gravity…


Causes cooler air to sink and condense water vapor.
Pulls condensed water back to Earth, where it flows downhill.


Energy can be extracted from flowing wind and water.



Sources of Energy


Energy via photosynthesis.


Chlorophyll stores solar energy in H-C bonds.
Water and carbon dioxide react to form sugar and oxygen.
6CO2 + 12H2O + light > C6H12O6 + 6O2 + 6H2O



H-C bonds release stored energy when broken (oxidized).
Organic respiration (breakdown of food by organisms).
Rapid thermal oxidation (combustion).



Sources of Energy


Energy from chemical reactions.
Energy stored in chemical bonds drives reactions.
 When bonds are broken, this energy may be used.


Exothermic reactions produce heat.
Some also produce light and usable energy.



Sources of Energy


Energy from fossil fuels.
Oil, natural gas, and coal derive from living organisms.
 These materials store energy in preserved H-C bonds.


Created by photosynthesis; solar energy from the past.
Thus, oil, gas, and coal represent “fossilized sunshine.”



Sources of Energy


Energy from nuclear fission.
Certain radioactive atoms can be fragmented.
 This process, called fission, yields tremendous energy.
 Fission energy is used to run nuclear power plants.




Sources of Energy


Energy from Earth’s internal heat.


Earth’s internal (geothermal) energy has 2 sources.
Residual heat from planet formation.
Heat from radioactivity.

Geothermal energy drives
tectonic plates.
 Heat lost through the
crust can be harnessed.




Oil and Gas
Industrial society depends on
oil and natural gas.
 Oil and gas are hydrocarbons.


Complex organic molecules.
 Made of hydrogen and carbon.
 From once-living creatures.




Many hydrocarbon types.
Found as complex mixtures.
 Pure compounds are separated
by refining.




Oil and Gas


Hydrocarbon properties due to size and structure.
Viscosity – Tendency to flow.
 Volatility – Tendency to evaporate.




Short-chain hydrocarbons (1 to 4 carbon atoms).
Low viscosity and high volatility.
 Vapors at room temperature.
 Examples: Methane, propane.




Oil and Gas


Moderate-chain hydrocarbons (5 to 40 C atoms).
Medium viscosity and volatility; liquids at room temp.
 Examples: Hexane, octane, nonane.




Long-chain hydrocarbons (> 40 C atoms).
High viscosity and low volatility; solids at room temp.
 Examples: Tar.




Oil and Gas Genesis


Oil and gas hail from plankton and marine algae.
Dead plankton and algae sink in quiet water.
 This organic material accumulates with fine mud.
 Under anoxic conditions, organic matter is preserved.
 Lithification forms a black shale petroleum source rock.




Oil and Gas Genesis


Burial to depths of 2 to 4 km heats the black shale.
Heating breaks the organics down into waxy kerogen.
 Kerogen-rich source rocks are called oil shales.


Continued heating breaks
down kerogen.
 Oil and gas form in
specific T ranges.


Oil and gas – 90o to 160oC.
 Gas only – 160o to 250oC.
 Graphite – >250oC.




Oil and Gas Genesis
The “oil window” T range is quite narrow.
 Oil window depth dictated by geothermal gradient.


25oC/km – 3.5 to 6.5 km depth.
 15oC/km – Below 11 km depth.




Hydrocarbon Systems
Oil and gas preservation is geologically rare.
 A known supply of oil is called an oil reserve.
 Oil reserves are geographically limited.
 Most oil is in super-giant fields in the Persian Gulf.




Hydrocarbon Systems


Creation of an oil reserve is
dependent on 4 features.
A source rock.
 A migration pathway.
 A reservoir rock.
 A trap.




These features must develop in
a specific order.



Hydrocarbon Systems


Source rocks and hydrocarbon generation.
Organic-rich black shale is the source of oil and gas.
 The organic matter is transformed within the oil window.
 The source rock does not store oil or gas.




Hydrocarbon Systems


Reservoir rocks and hydrocarbon migration.
Recoverable oil and gas are found in reservoir rocks.
 Reservoir rocks can store and transmit fluids.


Porosity – Open space in the rock that stores fluid.
Permeability – Ease of fluid movement through pore space.

Low – Small well yields.
High – Large well yields.



Hydrocarbon Systems


Reservoir rocks and hydrocarbon migration.
Oil and gas must migrate from source to reservoir.
 Migration is facilitated by density/buoyancy differences.


Oil floats on water; gas floats on oil.

Migration is promoted by fractures in rock.
 Reservoirs can leak to form an oil seep at the surface.




Hydrocarbon Systems


Traps and seals.
An oil or gas reserve requires trapping in the reservoir.
 Trap – A geological configuration that holds oil and gas.
 Seal – A low-permeability rock layer above a reservoir.
 Trap geometry is often crucial for fluid collection.




Hydrocarbon Systems


Traps and seals.


Anticline trap – A structural arch traps oil.



Hydrocarbon Systems


Traps and seals.


Salt-dome trap – Plastic flow in salt faults and folds rock,
forming traps.



Hydrocarbon Systems


Traps and seals.


Fault trap – Displacement juxtaposes rocks with varying
permeability.



Hydrocarbon Systems


Traps and seals.


Stratigraphic trap – Subtle depositional features create
traps.



Birth of the Oil Industry
Oil from seeps has been used for millennia.
 The 1st oil well was drilled in Titusville, Pa., in 1859.


Eased petroleum recovery.
 Initiated an oil boom.




Within years, 1,000s of oil wells
had been drilled.



Oil Exploration


The modern search for oil:
Early exploration involved searching for rare oil seeps.
 Investors realized systematic exploration was needed.
 Petroleum exploration became a subdiscipline of geology.




Oil Exploration
Complex, dangerous, and exciting; many steps.
 Geologists map sedimentary rocks.


Guide searches for source rocks, reservoirs, and traps.
 Rock sequences compiled from outcrops and drill cores.




Cross-sections show rock geometry, aid search.



Oil Exploration


Seismic reflection profiles subsurface layers.
Sound is “bounced off’ subsurface layers.
 Permits geologists to look for traps without drilling.
 Seismic imaging is conducted on land and at sea.
 Seismic studies are sophisticated and expensive.




Oil Exploration


Expensive drilling required to tap a potential trap.


A diamond rotary bit pulverizes rock.
High-density drilling mud cools the bit and lifts cuttings.
The heavy mud reduces blowouts.



Oil Exploration
As the bit advances, the open borehole deepens.
 Drill pipe is added by a drill derrick.
 Some derricks are mounted on offshore platforms.
 Platforms can drill many holes in many directions.




Oil Production
When a reservoir is encountered, drilling ceases.
 Steel casing prevents collapse of the hole.
 After casing, the well is pumped.




Oil Production


Primary recovery.
Uses reservoir pressure and pumping to extract oil.
 Inefficient; only able to recover about 30% of the oil.




Secondary recovery.


Fluids (steam, CO2) are injected to heat and push oil.



Hydrofracturing – Artificially increases permeability.



Oil Production


Crude oil must be refined.
Crude oil is distilled into separate compounds.
 Lighter molecules rise to the top of distillation columns.
 Heavier molecules remain at the bottom.




Alternative Hydrocarbons


Tar sands – Deposits of residual petroleum in sand.
Heavy oil, or bitumen, is residue of a former oil field.
 Lighter hydrocarbons are removed by bacterial digestion.
 The remaining hydrocarbon is too viscous to be pumped.
 Tar sands must be mined and processed.
 Extensive deposits in
Alberta and in Venezuela.






Oil shale – Shale containing abundant kerogen.
An oil source rock that has not been in the oil window.
 Burning transforms the kerogen into liquid hydrocarbon.
 Large supplies occur in…


Estonia.
Scotland.
China.
Russia.
Western United States.





Natural gas – Volatile, short-chain hydrocarbons.
Methane, ethane, propane, butane, and others.
 Gas floats on top of oil in a reservoir.
 Below the oil window, hydrocarbons are turned into gas.
 Natural gas is more abundant than oil; a cleaner fuel.
 Utilization requires expensive, high-pressure pipelines.






Gas hydrate – Methane (CH4) in a cage of water ice.


CH4 is from bacterial decomposition of organic matter.

Methane hydrate forms in water depths exceeding 300 m.
 Stores more carbon than all other reservoirs combined.
 Recovery is not currently feasible.




Coal
Black, brittle, carbonaceous sedimentary rock.
 Remains of organic matter from vegetation.
 Important global energy source; CO2 emitter.




Only found in rocks younger than 420 Ma.



Coal


Coal-forming eras.


Carboniferous (354 – 286 Ma).
Warm climate.
Broad epicontinental seas.
Tropical deltaic wetlands.



Cretaceous (144 – 65 Ma).



Coal Formation


Vegetation accumulates in an O2-free setting.



Absence of oxygen prevents organic matter decay.
Marine deltas.
 Tropical coastal wetlands.




Sea level rise and fall buries wetland deposits.



Coal Formation
Coal formation requires heat and pressure.
 Compaction and decay turns plant debris into peat.


Approximately 50% carbon.
 Readily cut out of a wetland deposit.




Coal Formation
Peat is buried several km in a subsiding basin.
 Burial compaction squeezes out water.
 At depth, heat alters the plant material.


H, N, and S are expelled as gases; C content increases.
 At 70% carbon, this solid material becomes coal.




Coal Rank


Classification based on the carbon content.
Peat
Lignite
Bituminous
Anthracite

50% C
70% C
85% C
95% C

Anthracite forms by metamorphism in an orogenic belt.
 Higher-rank coal yields more energy when burned.




Coal Rank



Coal Mining


Coal is part of a specific sedimentary sequence.
Shallow marine, coastal, fluvial, and deltaic environments.
 Tropical to subtropical.




To be mined, coal must be…
Within reach.
 Thick enough (1 – 3 m).




Coal Mining
Huge coal reserves have been discovered.
 Mining type depends on the depth of the coal seam.


Within 100 m, coal is strip mined.
 For deeper coal seams, underground mining is required.




Coal Mining


Strip mining – Landscape destroyed to reach coal.


A large drag line bucket is used to scrape off overburden.
Spoil is stockpiled nearby for later use during reclamation.



Exposed coal is removed and the excavation is reclaimed.
Excavation is backfilled with spoil and soil, then planted.



Coal Mining


Underground mining – Coal removed by tunneling.
For coal deeper than 100 m, shafts are advanced to seam.
 Tunnels excavated along the seam remove the coal.
 Coal mining is specialized, expensive, and dangerous.


Tunnels can collapse.
Methane gas.

Asphyxiation.
Explosions.
Black lung disease.



Coal


Coal can yield energy without direct combustion.
Coalbed methane – Natural gas trapped in buried coal.
 Coal gasification – Coal is changed to a combustible gas.


Old coal gas plants in many cities are now waste sites.
Modern coal gasification is much less polluting.



Coalbed Fires


Runaway coal combustion underground.
Coal can be ignited in place by lightning, spontaneous
combustion, gas explosions, or deliberate ignition.
 Difficult to extinguish, these fires may burn for decades.
 Produce hazards like toxic fumes and ground collapse.




Nuclear Power


Energy from breaking apart atomic nuclei.
Neutrons strike the fuel and start fission.
 Fission splits a large nucleus into smaller fragments.


Nuclear reactors are contained in a domed
building.
 Reactors are loaded with uranium oxide fuel rods.




Nuclear Power


A high-speed neutron initiates fission creating…
Nuclear fragments.
 A large yield of energy.
 More high-speed neutrons.


Neutrons fuel a sustained
nuclear chain reaction.
 Control rods absorb
neutrons, slowing fission.




Nuclear Power


Fission produces enormous amounts of energy.
High-pressure steam is created in a closed reactor loop.
 Heat is transferred to an external water loop.
 Steam in the external loop is used to spin electrical turbines.




Nuclear Power
Nuclear power is a major source of electricity.
 Nuclear power emits zero greenhouse gases.
 Nuclear power use likely to increase in the future.




Nuclear Power


The geology of uranium.
Uranium – 235 (235U) is the most common nuclear fuel.
 Uranium has 2 major isotopes.






U – 99.3% (not fissionable).
235
U – 0.7% (fissionable).
238

U must be enriched 2 to 3 times to be fissionable.

235



Nuclear Power


The geology of uranium.


Uranium occurs naturally in all rocks; amount varies.
Uranium dissolved from minerals is transported by water.
Dissolved uranium solidifies in mineral veins and fractures.



Radiation detectors are used to find uranium.



Nuclear Problems
Nuclear power is expensive.
 Loss of reactor control may start core “meltdown.”


Molten reactor materials could bore through containment.
 A steam explosion could then spread radioactivity.




Nuclear Problems
Plant safety is a major concern.
 Extensive efforts applied to thwart terrorism.
 Nuclear accidents are rare but have occurred.


1986 – Chernobyl (Ukraine) spread radioactivity globally.
 1979 – Three Mile Island (Pennsylvania, U.S.).




Nuclear Problems


Generates highly radioactive wastes.
Extremely toxic, wastes are poisonous for 1,000s of years.
 High-level waste storage is a major societal issue.




Wastes also generated by processing uranium ore.



Other Energy Sources


There are a number of other energy options.
Geothermal energy.
 Hydroelectric power.
 Wind energy.
 Solar power.




Geothermal Energy


Energy from Earth's internal heat.
Geothermal gradient: Earth becomes hotter with depth.
 Geothermal gradients vary (15oC/km to 50oC/km).
 High geothermal gradients: hotter at shallower depths.




No wastes; no greenhouse gases or air pollution.



Geothermal Energy


Geothermal energy is utilized in 2 ways.
Hot water is pumped and used to heat buildings.
 Steam is used to drive electric turbines.




Geothermal is a dominant energy source in some
areas (e.g., Iceland, New Zealand).



Hydroelectric Power
Flowing water turns potential energy into kinetic energy.
 This energy works by eroding and moving sediment.
 Hydroelectric power dams arrest the flow of water.
 Water is directed past turbines to create electricity.
 Some dams generate electricity via tidal flux.




Hydroelectric Power


Positive aspects.
Reduces the risk of floods.
 Impounds water for drinking,
irrigation, and recreation.
 Provides renewable energy
without creating wastes.




Hydroelectric Power


Negative aspects :
Dams destroy valued landscapes and alter ecosystems.
 Reservoirs accumulate the sediment load of the river.


Sediments added to reservoirs require expensive dredging.
Erosion is accelerated downstream of dams.



Wind Energy


High-tech wind farms are sprouting worldwide.
Wind drives a large turbine to produce electricity.
 Wind-derived electricity is renewable and carbon-free.




Drawbacks.
Wind farms have negative aesthetic impacts.
 Turbine blades are noisy and kill birds.




Solar Power
By far the most abundant source of energy to the surface.
 Solar energy dwarfs that of hydrocarbon resources.
 But solar energy is hard to utilize because it is…


Diffuse.
Highly variable on a seasonal and daily basis.
Difficult to convert into more usable forms of energy.



Solar Power


There are two ways to use solar energy directly.
Solar collectors concentrate sulight for heating.
Photovoltaic (PV) cells convert light directly into electricity.



Both are useful for small buildings; not large cities.



Biomass


Biomass – Energy from plant and animal matter.
Early humans used biomass (wood, charcoal, dung).
 To be useful today, biomass must be grown quickly.
 Ethanol – Alcohol derived from corn.


Burned as a motor fuel.
Produced in large quantities.
Unproven as a gasoline replacement.



Hydrogen Fuel Cells
Produce electricity via chemical reactions.
 Hydrogen reacts with oxygen in an electrolyte bath.







Generates electricity, heat, and H2O.
The reaction is environmentally benign.

Fuel cells are useful as engines for motor vehicles.


Technological issues must be addressed 1st.
Safely storing compressed hydrogen.
Producing hydrogen efficiently.
Distributing hydrogen.



Energy Problems
Global energy use increased dramatically.
 Use reflects rapid expansion of industrialization.
 Oil, the dominant energy source, is dwindling.
 Many countries import
oil to meet demands.




Energy Problems


The 1970s energy crisis.
In 1973, the Organization of Petroleum-Exporting
Countries (OPEC) began to limit the volume of exports.
 The price of oil skyrocketed, resulting in fuel shortages.
 Gas stations witnessed long lines for the 1st time.




Energy Problems


The 1970s energy crisis.


The result was a new understanding of energy by all.
Regulations lowered speed limits and raised mileage stds.
Goods tended to be smaller and more energy-efficient.
A new consumer ethos was born.

Reducing home energy usage.
Carpooling.
Public transportation.



Energy Problems


The oil crunch - Renewable vs. nonrenewable.


Renewable – Can be replaced within months to years.
Biomass, solar, wind, geothermal, hydroelectric.



Nonrenewable – Replacement requires hundreds to
millions of years.
Oil, natural gas, coal, uranium ores.



Energy Problems


The oil crunch.
We consume nonrenewable resources too rapidly.
 We face running out of nonrenewable resources.
 For each resource, the question is “When?”
 The answer, for oil, may be “Soon.”




Energy Problems


The oil crunch.
Oil extinction will occur by 2050 to 2150.
 Future historians will see the “Oil Age” as a 200-year era.
 We are now close to the peak of global oil production.
 Humanity faces many changes as oil runs out.




Energy Problems
The oil crunch: What can humanity do?
 There are many sources of energy that we can use.


Tar sands and oil shales.
 Coal.
 Natural gas.
 Coalbed methane.
 Uranium.
 Renewables.


Each energy source has associated difficulties.
 Society faces difficult choices.




Environmental Issues


Energy production creates environmental insults.
Oil drilling and production scars the landscape.
 Spills from oil storage tanks, pipelines, and ships...


Contaminate surface water and ground water.
May devastate large areas of coastline.


Coal mining creates pits, spoil piles, and acid mine runoff.



Environmental Issues


Air pollution results from fossil fuel combustion.
Unburned hydrocarbons add to photochemical smog.
 Sulfur dioxide (SO2) from coal yields acid rain.




CO2 addition fuels global warming and climate change.



This concludes the
Chapter 14
Energy Resources

LECTURE OUTLINE

earth

Portrait of a Planet

Third Edition
©2008 W. W. Norton & Company, Inc.


Op ch14 lecture_earth3, solar energy

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