Environmental Geology Spring 2010 – Text Notes
Energy Resources

Types of Resources:
Renewable Resources: replenished on a human time scale (a few generations), or those used without depletion of supply

Non-renewable resources: not produced at present, or at rates much slower than current rates

Resource: currently or potentially available includes both know and undiscovered sources

Reserves: concentration of a material in such a form that extraction is economically, technically, and legally possible at the current time.  Reserves are not static: affected by economics; technological advances; amount of resource available

Fluctuations occur because of changing demand, discovery of new deposits, changing technologies

Example: Gold: price controlled in U.S. at $35 per troy ounce in 1968.  In 1980 price was allowed to go to world market price and climbed to over $1000 per troy ounce.  Heap leach mining is feasible at these prices but was unrealistic at $35 per troy ounce.

Example: Drilling in the Arctic National Wildlife Refuge.  These resources were not counted in the U.S. reserves because they were legally off-limits as a result of the 1992 ban on drilling, exploration and production in this area.  While the environmental groups have successfully blocked drilling activities in this region to this point, it is likely only a matter of time before the resource is tapped.

Response to limited supply:
Find more sources
Find substitutes
Recycle
Conserve
Do without (That’s Just Downright Un-American!!!!)

Fossil Fuels:
1.    Oil
2.    Natural Gas
3.    Coal
4.    Shale Oil
5.    Tar Sand

Oil is various liquid hydrocarbons (H + C)
Natural gas is gaseous hydrocarbons (CH4 – methane is most common)

Formation:
Need large accumulation of organic matter
Rapid burial, avoid decay by biological means, avoid reaction with oxygen
Usually in marine environments

Burial increases pressure and temperature; chemical reactions break down complex organic molecules.

Early stage: heavy hydrocarbons (asphalt)
Middle stage: lighter hydrocarbons (oil)
Later stage: Natural gas; above about 100 degrees C all organics are converted to natural gas

Exact time needed for conversion to oil and natural gas is unknown: virtually no petroleum in rocks younger than 1 to 2 million years old.

Conversion occurs in the source rock (usually a shale or limestone).

Migration occurs after conversion to liquid or gas; oil and gas moves along with circulating formation fluids (water); oil and gas are less dense than water so they float; rise to the surface and escape if not trapped by a low permeability barrier (often a shale layer)

Reservoir Rock is often sandstone or siltstone, but may be fractured limestone, or sometimes fractured igneous and metamorphic rocks.

Illustrated diagrams of various traps (see text for diagrams): Anticlinal trap; fault trap; reef trap; stratigraphic trap; salt dome.

Supply and Demand:
Oil is King!!!

Measure oil in barrels: 1 barrel is approximately 42 gallons

We have consumed over 750 billion barrels with over half of this in the last decade

Estimated remaining world reserves is about 1,000 – 1,450 billion barrels

Present word consumption is between 24 and 28 billion barrels per year.

About 40 years of reserves at current rate of consumption (so out to about 2050 or so, who cares, I’ll be dead!!).

Estimated total resource is about 3,000 billion barrels

Estimated future demand is anticipated to double to 50 billion barrels per year.  Considering this we might be able to stretch the resource for about 65 years (2070 or so)  (me and my kids will probably be dead, but my grandkids and great grandkids will likely still be around!!).

U.S. oil resources including the amount already consumed  accounted initially for about 10% of world resources.  We have consumed over 200 billion barrels of the U.S. resource

Estimated U.S. resource as of 1997 was about 77 billion barrels

Are other new sources of oil and natural gas available?
•    Best and easiest prospects already discovered
•    Exploration slowed in 80’s and will likely not resume in many areas of the continental U.S.
•    Many of the areas not yet explored are in igneous and metamorphic areas.

Enhanced recovery:  This accounts for about 1/3 of oil extracted today

Water flooding
•    Burning in-situ, reduces viscosity, increases pressure in formation
•    Steam injection, reduces viscosity, increases pressure in formation
•    Carbon dioxide injection, increases pressure in formation
•    Surfactant injection, washes oil from sediments

Oil Shale: sedimentary rock containing waxy solid hydrocarbon called kerogen.  U.S. has about 2/3 of world supply.
•    Must crush and heat at over 500 degrees C to distill the shale oil
•    Must remove huge amounts of rock to obtain small amount of oil – much waste product
•    Large amounts of water required to process

Tar Sands: sedimentary rock containing tar-like petroleum, that either never fully matured or the lighter gases and liquids volatilized.
•    Must be crushed and heated to extract oil
•    Waste disposal is a problem

Coal:
Remains of dead plants
Burial in swampy environment
Much of the coal we mine today was formed about 300 million years ago

Increasing heat content as you go down the list
•    Peat
•    Lignite – soft brown coal
•    Bituminous – this is what is currently produced in Wyoming that fuels most of our power plants
•    Anthracite – metamorphic grade of coal

Coal Reserves and Resource:
World reserves about 650 to 1,000 billion tons
Total world resource about 10 trillion tons
U.S. has about 30% of world reserves about 200-500 billion tons (we are the king of coal)

Total U.S. resource is about 2 trillion tons

We use about 1 billion tons/year

Alternate Energy Sources:

Nuclear
Fission – splitting of atoms; use uranium 235, which only accounts for about 0.7% of all uranium.

Problems: accidental release, waste disposal; not viewed as a strong player over the next few decades

Solar:
Passive solar – heat an object and then use the heat

Direct solar – conversion to electricity using solar cells: must store energy, requires large space for solar cells (shading the Arizona desert), cells contain toxic elements that must eventually be disposed.

Geothermal:
Magma warms rocks and produces heat which generates hot water or steam to drive electrical turbines or is used for direct heating.
•    Clean
•    Limited numbers of sites
•    Sites can be exhausted

Shallow heating and air conditioning loops that tap the subsurface or groundwater are also examples of geothermal energy utilization.

Hydroelectric:
Cheap, clean, efficient, limited numbers of sites, eventually become choked with sediment

Wind: cheap, clean, renewable, requires large space, need steady relatively low velocity winds, may represent an unpleasant landscape (example is system being built off the U.S. northeast coast).

Biomass: (wood, crop residue, paper, garbage, sewage)
Renewable, often resolves other disposal problems (as example conversion of excess poultry litter to energy in Northwest Arkansas removes this as a waste product in this area of the state.).