Classroom presentations
to accompany
Understanding Earth, 3rd edition
prepared by
Peter Copeland and William
Dupré
University of Houston
Chapter 22
Energy and Material Resources from the Earth
Part IV
Conserving Earth’s Bounty
Energy and Material
Resources
Thomas Kitchin/Tom Stack
Fig. 22.1
Natural resources
• Most geologists are employed
in looking for some kind of
resource.
• Resources range from
petroleum to precious metals
to water.
Resource
• A material that is both useful and
available in useable quantities.
• A renewable resource is one that is
produced faster than it is depleted.
Reserves
• Resources that are identifiable and
recoverable under today's economic
conditions
• Conditional resources: not economic
at the moment.
Energy Mix in the U.S.
1850–1997
Fig. 22.2
Photosynthesis
and Fossil Fuels
The Carbon
Cycle
Fig. 22.3
Fossil fuels
• Decayed organic material (plants)
• Must have relatively rapid burial
FOSSIL FUELS ARE A
NONRENEWABLE
RESOURCE
Hydrocarbons—oil and gas
Oil formation
1) Relatively large quantity of organic
matter
2) Rapid burial (before oxidation)
3) Subsequent chemical reactions [f(P,T)]
transform decaying organic matter into
hydrocarbons.
How do oil and gas deposits form?
• Production of large amounts of organic
material (mainly microscopic plants and
bacteria)
• Preservation in a reducing (oxygen-poor)
depositional environment (e.g., restricted
ocean basin)
• Burial causes increased heat and pressure,
resulting in maturation (the physical and
chemical breakdown of organic matter into a
liquid or gaseous hydrocarbon compounds) in
a source rock.
There’s more:
• Migration of fluids out of the source rock
into a more permeable reservoir rock.
• Trapping of fluids must occur by
encountering an impermeable seal.
• In short, you need
– Production
– Preservation
– Maturation
– Migration
– Trapping
Thermal conditions of oil formation
• Relatively narrow temperature range:
≈50–200°C (also depends on time)
• Temperature and duration determine
type of hydrocarbon:
oil wet gas dry gas gone
• Duration of process could last millions
of years
Environments of oil formation
• Continental shelf
• Continental rise
• Some nonmarine basins
Reservoirs
• For oil to be useful, it must
accumulate in concentrated and
accessible areas. Such spots are
called reservoirs.
• Accumulation is possible because oil
and gas are low-density fluids that
can migrate through the pore space in
rocks.
Reservoirs
To create a reservoir, the migration of the
fluids is retarded by cap rock.
Cap rocks
Reservoir rocks
shale
sandstone
gypsum
limestone
salt
limestone
Trap
Combination of cap rock and reservoir
rock favorable for petroleum
accumulation
• Stratigraphic trap
• Structural trap
Anticlinal Trap
Fig. 22.4a
Fault Trap
Fig. 22.4b
Stratigraphic Trap
Fig. 22.4c
Salt Dome Trap
Fig. 22.4d
Dry Holes
• Many potential reservoirs exist that
are free of hydrocarbons.
• Source rocks may have enough
organic matter but may never have
been hot enough.
Oil distribution
Most oil is found in Cenozoic rocks,
which have the best chance of
preservation (erosion, metamorphism).
How do we explore for oil?
• Map surface geology (use surface
geometry to interpret subsurface
conditions)
• Seismic exploration (good way to get
lots of information but subject to
interpret)
• Drilling, coring (more detailed
information from smaller area—like
seismic, very expensive)
How much oil is left?
• Proven reserves: 700 billion barrels
(over half in Middle East)
• Petroleum resources: 2 trillion barrels
• 1997 consumption: ~70 million barrels
per day
• At this rate reserves will last between 25
and 80 years.
This assumes no increase
in the rate of consumption, but
• Between 1985 and 1995, consumption
of oil in the world increased by 16%.
• The increase in Latin America was
30%.
• The increase in Africa was 40%.
• The increase in Asia was 50%.
Estimated
World
Reserve of
Crude Oil
Fig. 22.5
Total World Reserves
Fig. 22.7
Coal
• Coal is usually formed in swamps
• 1st stage - peat (high C, high H20)
• P,T  loss of gases, toward higher C
Ranks of coal:
Anthracite
Bituminous
Subbituminous
Lignite
Coal
• High sulfur is bad—H2SO4 is produced
during burning.
• Principle coal producing areas in United
States are Appalachia, Wyoming, New
Mexico, and Colorado.
Formation
of Coal
Fig. 22.8
Coalfields of the United States
Fig. 22.9
Strip Mining Coal in
Pennsylvania
Peter Kresan
Fig. 22.10a
Reclaimed Land in Pennsylvania
Peter Kresan
Fig. 22.10b
Alternatives to fossil fuels
1. Nuclear energy
Advantage:
virtually inexhaustible supply
Disadvantage:
dangerous waste
Possible Nuclear Waste
Contamination
After R.E. Gephart, 1998
Alternatives to fossil fuels
2. Solar energy
Advantage:
virtually inexhaustible supply
Disadvantage:
very expensive with current technology
Solar Cells
Fig. 22.11
Ned Gallate/The Stock Market
Alternatives to fossil fuels
3. Geothermal energy
Advantage:
cheap and clean
Disadvantages:
cannot be transported long distances
Geothermal energy
• Must have a concentrated heat source
near the surface: magma chamber
with porous rocks above
• Cool water pumped into hot rocks, hot
water or steam extracted (rocks may
be as cool as 80°C)
• Producing: Iceland, France
• Experimenting: New Mexico,
California
Geothermal Energy to Electricity
Pacific Gas and Electric
Fig. 22.12
World Energy Demand
1971-2010
Fig. 22.13
Mineral deposits
• If deposited in concentrated volume,
we get veins or lodes.
• If deposited in large volume, we get
disseminated deposit.
• grade: The relative quantity of ore in
an ore body (gold ≈0.05 oz/ton)
Mineral deposits
• hydrothermal deposits: minerals
deposited from hot waters usually
associated with igneous intrusions
• These fluids carry “low temperature
ions”; when the fluids cool off (near
surface) the solubility goes down and
minerals with Pb, Fe, Hg, Cu, Zn, Ag,
Au, etc. are precipitated.
Iron Ores
Siderite
Pyrite
Magnetite
Hematite
Chip Clark
Fig. 22.14
Native Gold
on a Quartz
Crystal
Chip Clark
Fig. 22.15
Hydrothermal Ore Deposits
Fig. 22.18
Vein Deposit of Gold and Silver
Quartz
Peter Kresan
Fig. 22.19
Metal Sulfide Ores
Galena
Chip Clark
Cinnabar
Pyrite
Sphalerite
Fig. 22.20
Copper Ores
Malachite
Chalcopyrite
Chip Clark
Chalcocite
Fig. 22.21
Open-pit Copper Mine, Arizona
Bob Lynn/Cyprus Minerals
Fig. 22.22
Layered Chromite Deposit
Spence Titley
Fig. 22.23
Manganese
Nodule
Chip Clark
Fig. 22.27
Other igneous sources
• Pegmatites
• Kimbelites
• Layered igneous complexes
Sedimentary mineral deposits
• Banded iron formations
• Placers
• Clays
• Sand and gravel
Precambrian Banded Iron Deposits
Spence Titley
Fig. 22.24
Fig. 22.25
Plate Tectonics and
Mineral Deposits
Fig. 22.26
Major Metallic Ore Deposits on Land
Fig. 22.28
Major Nonfuel Sub-sea Ore Deposits
Fig. 22.29
Metal Consumption (by Weight)
in the United States
Fig. 22.16
Enrichment
Factors
Required to
Make an
Economic
Deposit for
Various
Natural
Resources
Kanai National Wildlife Refuge
John Hyde/Bruce Coleman/Picture Quest
Wildlife
Affected by
an Oil Spill in
Alaska
UPI/Corbis-Bettmann
Fig. 22.6