Transcript energy_resources

Earth Resources
Geology Today
Chapter 16
Barbara W. Murck
and
Brian J. Skinner
Petroleum, solar energy,
and biomass - California
N. Lindsley-Griffin, 1999
Renewable and Nonrenewable Resources
Renewable resource - can be replenished or regenerated on the
scale of a human lifetime.
Nonrenewable resource - being consumed faster than it is being
replaced.
N. Lindsley-Griffin, 1999
Energy
Resources
Nonrenewable fossil fuels
(oil, gas, coal) account for
90% of energy used in the
United States.
But - nonrenewable fossil
fuels are nearly used up.
Renewable fuels: < 10%
Energy lost - 49% - is due
to inefficient use and
limits of technology.
Fig. 16.3, p. 473
N. Lindsley-Griffin, 1999
Fossil Fuels
N. Lindsley-Griffin, 1999
Fossil fuels include all forms of organic matter
trapped in rock: peat, coal, oil, natural gas, tars.
Less than half the known petroleum reserves can
be recovered because of technological limitations.
Fig. 16.15, p. 484
Energy
Resources
The world’s energy use has changed
through time as new discoveries and
technology became available.
Wood (pre-1875)
Coal (1875-1950)
Oil (mid-20th
century)
© Houghton Mifflin 1998; N. Lindsley-Griffin, 1999
Natural Gas (late
20th, early 21st)
Alternatives will be
important in 21st
Energy
Resources
Demand for energy since 1860:
Total fuel use has increased as world population
increased. Only fuel wood use has decreased
among individual energy sources.
Fig. 16.13, p. 483
N. Lindsley-Griffin, 1999
Energy
Resources
Fuels of the future balanced against two possible
demand predictions.
(Assumes the use of coal, our environmentally
dirtiest fuel, does not expand.)
Fig. 16.14, p. 483
N. Lindsley-Griffin, 1999
Fossil Fuels
Fossil fuels form when plants use
photosynthesis to absorb the sun’s
energy and use it to combine water
and carbon dioxide, creating oxygen
and carbohydrates.
Burning a fossil fuel reverses the
process and releases heat.
Coal
Petroleum
Oil
Natural Gas (methane)
Oil Shales
Tar Sands
U.S. Geological Survey
N. Lindsley-Griffin, 1999
Fossil Fuels
Any organic matter that escapes
decay and is buried in sediments
becomes part of the reservoir of
stored solar energy.
The total amount of organic matter stored this way is less than 1% of all the
organic matter that has been formed by plants and animals over geologic time.
Fossil Fuels
are composed
of
hydrocarbons
N. Lindsley-Griffin; Dolgoff, 1998
Fossil Fuels
Undiscovered fossil fuel resources may potentially
be found in any unexplored sedimentary rock.
The largest petroleum reserves are in the Middle East.
N. Lindsley-Griffin, 1999
Coal
Coal begins forming when thick accumulations of
plant remains produce peat, a loose water-saturated
aggregate of biogenic sediment
Pennsylvanian Coal Swamp, The Field Museum, Chicago
N. Lindsley-Griffin, 1999
Coal
Coalification and diagenesis dewater and
compact plant remains.
Peat has only 60% carbon; coal has 80% carbon.
N. Lindsley-Griffin, 1999
Fig. 16.5, p. 475
Coal
The United States has ample reserves of coal, most of it
either the lowest grade - lignite - or the middle grade bituminous coal. Only small reserves of anthracite, the
highest grade coal, occur in the Appalachian Mountains.
Fig. 16.7, p. 477
N. Lindsley-Griffin, 1999
Coal
N. Lindsley-Griffin, 1999
Coal, a sedimentary rock, occurs in layers, associated with
other sedimentary rocks like shale and sandstone.
It is mined by stripping off the overburden, removing the coal
layer, and backfilling the hole with the waste rock.
Coal
Strip mining of coal looks messy, but after
restoration it may be hard to tell the difference
Restoration: Refill pit with tailings
Cover with stockpiled soil
Shape to “natural” appearance
Replant with native vegetation
N. Lindsley-Griffin, 1999
Petroleum
Organic-rich limestone - a good source rock
Coral reef, Mexico
Requirements:
Organic-rich source rocks
Permeable reservoir rock
Impermeable reservoir cap rock
Oil traps
N. Lindsley-Griffin, 1998
Petroleum
Certain conditions of
pressure and temperature
are required to create
petroleum - the
hydrocarbon window
Oil forms in a source rock
like organic shale.
It migrates until it is
trapped by a cap rock.
It resides in a reservoir
rock like sandstone.
N. Lindsley-Griffin, 1999
Petroleum
Reservoirs should have high
porosity, permeability
Examples: sandstone, conglomerate, cavernous
limestone, highly fractured rocks (even granite)
N. Lindsley-Griffin, 1998
Petroleum
N. Lindsley-Griffin, 1999
Oil migrates up dip because it is less dense
than rock. Oil floats on water of the
saturated zone; natural gas (methane)
floats on top of the oil.
Fig. 16.10, p. 480-481
Petroleum
N. Lindsley-Griffin, 1999
Faults may themselves seal off migration,
or may place impermeable rock against
the reservoir to block escape
Fig. 16.10, p. 480-481
Petroleum
N. Lindsley-Griffin, 1999
Angular unconformity traps oil in lower
dipping layers
Fig. 16.10, p. 480-481
Petroleum
N. Lindsley-Griffin, 1999
Sedimentary facies changes create lensshaped wedges or pinch-outs that may
serve as traps in some conditions.
Fig. 16.10, p. 480-481
Petroleum
N. Lindsley-Griffin, 1999
Salt domes are derived from less dense halite
layers that punch up through overlying
layers until they reach neutral buoyancy.
Folded and cut-off layers make traps.
Fig. 16.10, p. 480-481
Petroleum
N. Lindsley-Griffin, 1999
Fossil reefs are bulbous lenses interbedded
with normal layers. They trap oil derived
from lower source rocks.
Fig. 16.10, p. 480-481
Petroleum
Summary of petroleum traps.
You should be able to recognize where oil and gas will
accumulate, as well as good candidates for source, cap,
and reservoir rocks.
Lens or Pinch-out
Unconformity
Houghton Mifflin 1998; Dolgoff, 1998; N. Lindsley-Griffin
Fault
Anticline
Salt Dome
Petroleum
Petroleum can be extracted and transported
in environmentally friendly ways.
Alaska’s North Slope: Drill sites are
built on thick pads of gravel that
protect the permafrost from melting
Alaska Pipeline crossing
the Brooks Range on
elevated, cooled supports
U.S. Geological Survey; N. Lindsley-Griffin, 1998
Petroleum
Petroleum reserves - the known but not
yet exploited resources - are located near
ancient and modern plate boundaries.
Divergent (rifts) and convergent margins are best.
N. Lindsley-Griffin, 1999
Dolgoff, 1998; Houghton-Mifflin
Tar Sands
Tar is dense, very viscous, will not
flow easily, and cannot be
pumped like oil.
In tar sands, the pore spaces are
filled by tar.
Much of the world’s reserves of tar sands
are under Alberta, Canada, in the
Athabasca sandstone, where the sand
grains are cemented by tar.
Smaller deposits are in Venezuela and
the former Soviet Union.
Fig. 16.11, p. 482
N. Lindsley-Griffin, 1999
Tar Sands
N. Lindsley-Griffin, 1999
Athabasca sandstone is strip-mined, then heated
by hot water and steam to soften the tar and
loosen it from the rock.
Fig. 16.11, p. 482
Oil Shales
Oil shales contain
kerogen, a waxy organic
substance that forms at
lower temperatures
than oil and gas.
Because the removal process
is very expensive, oil shales
cannot be considered a
potential resource until the
oil removed yields more
energy than the energy
required to produce it.
Fig. 16.12, p. 482
N. Lindsley-Griffin, 1999
Oil Shales
The world’s largest oil
shale deposit lies under the
corner where the states
Colorado, Utah, and
Wyoming come together.
The Green River oil shale
formed during the Eocene,
in large shallow lakes.
It contains about 2000
billion barrels of oil.
N. Lindsley-Griffin, 1999
Earth’s
Energy
Budget
Fig. 16.16, p. 485
Earth’s energy comes from:
external sources (solar radiation), internal sources (geothermal energy), and
Earth-Moon-Sun interactions (tidal -- a very small component)
N. Lindsley-Griffin, 1999
Renewable Energy Resources
Sun’s energy:
Solar
Wind
Waves
Tides
Hydroelectric
Internal energy:
Nuclear fission
Nuclear fusion
Geothermal
N. Lindsley-Griffin, 1998
Wind
Energy
N. Lindsley-Griffin, 1999
Wind energy is obtained from wind turbines, fan
blades driven by sustained wind velocities of > 12
kph. Two wind turbines provide part of Lincoln
Electric System’s power.
Wind Farm, Palm Springs, CA -- Fig. 16.17, p. 486
Hydroelectric Energy
Hydroelectric power is generated when flowing water driven by
gravity turns the blades of a turbine to generate electricity.
Drawbacks: cost of dam building, ecological damage to natural
stream systems, silting of reservoirs
Fig. 16.18, p. 487
N. Lindsley-Griffin, 1999
Nuclear
Energy
Nuclear energy is heat
produced by controlled
nuclear reactions atoms of one species of
chemical element are
transformed into atoms
of another species by
nuclear change.
Fig. 16.19, p. 488
N. Lindsley-Griffin, 1999
Nuclear Energy
Fission occurs when heavy atoms are split into lighter atoms.
A continuous chain reaction is caused when neutrons ejected
from the nucleus strike other fissionable atoms, causing them to
split. An uncontrolled chain reaction results in an explosion.
Fusion occurs when two light atoms combine into a heavier atom.
N. Lindsley-Griffin, 1999
Houghton-Mifflin; Dolgoff, 1998
Nuclear
Energy
Nuclear power plants use the heat energy from fission to produce
steam that can drive turbines and generate electricity.
17% of the world’s electricity comes from nuclear fission. France,
Japan, and most European countries have so little fossil fuel that
they depend heavily on nuclear power.
Nuclear power is considered to be a clean source of energy because
it does not produce harmful emissions like fossil fuels.
Drawbacks - accidents can release toxic gases, radiation;
radioactive waste must be isolated and stored for long half-lives.
N. Lindsley-Griffin, 1999
Geothermal
Energy
Geothermal energy is derived
from hydrothermal reservoirs,
underground systems of hot
water or steam that circulate in
fractured or porous rocks.
To be efficient, temperatures of
>200o C and depths of < 3 km are
required.
N. Lindsley-Griffin, 1999
Geothermal
Energy
Most of the world’s
hydrothermal reservoirs
occur:
near plate boundaries
in recently volcanic areas
where hot rocks or magma are close
to surface
Mexico’s Cerro Prieto
geothermal plant is located at
the southern end of the
Imperial Valley
Fig. B16.1, p. 494
N. Lindsley-Griffin, 1999
Geothermal
Energy
Advantages:
renewable
environmentally clean
economical
Drawbacks:
practical only in limited areas
high initial capital investment
markets must be fairly close
actual installations unsightly
N. Lindsley-Griffin, 1999; Houghton-Mifflin, Dolgoff, 1998