Chapter 15 (Fossil Fuels and the Environment)

Oil shale

A fine-grained sedimentary rock containing or- ganic matter (kerogen). When heated to 500°C (900°F) in a process known as destructive distillation, oil shale yields up to nearly 60 liters (14 gallons) of oil per ton of shale. If not for the heating process, the oil would remain in the rock. The oil from shale is one of the so-called synfuels

Coal

A fossil fuel that forms underground from partially decomposed plant material.

Black Shale (tight) Natural Gas

According to the U.S. Geological Survey, Black De- vonian shale over 350 million years old buried a kilometer or so beneath northern Appalachia, contains about 500 trillion cubic feet of natural gas (mostly methane) of which10% or more may be ultimately recovered.

Allowance Trading

An innovative approach to managing U.S. coal re- sources and reducing pollution is allowance trading, through which the Environmental Protection Agency grants utility companies tradable allowances for pollut- ing: One allowance is good for one ton of sulfur dioxide emissions per year.

Methane hydrates

Beneath the seafloor, at depths of about 1,000 meters, there exist deposits of methane hydrate, a white, ice-like compound made up of molecules of methane gas, molecular "cages" of frozen water. The methane has formed as a result of microbial digestion of organic matter in the sediments of the seafloor and has become trapped in these ice cages.

mountaintop removal mining

Coal mining in the Appalachian Mountains of West Virginia is a major component of the state's economy. However, there is growing environmental concern about a strip-mining technique known as "mountaintop removal". This technique is very effective in obtaining coal as it levels the tops of mountains. But as mountaintops are destroyed, valleys are filled with waste rock and other mine waste, and the flood hazard increas- es as toxic wastewater is stored behind coal-waste sludge dams.

Fossil Fuels

Fossil fuels are forms of stored solar energy. Plants are solar energy collectors because they can convert solar energy to chemical energy through photosynthesis. The main fossil fuels used today were created from incomplete biological decomposition of dead organic matter (mostly land and marine plants).

Coal Mining and the Environment

In the United States, thousands of square kilometers of land have been disturbed by coal mining, and only about half this land has been reclaimed. Reclamation is the process of restoring and improving disturbed land, of- ten by re-forming the surface and replanting vegetation. Unreclaimed coal dumps from open-pit mines are numerous and continue to cause environmental problems.

Clean Air Amendments of 1990

Legislation as part of the Clean Air Amendments of 1990 mandated that sulfur dioxide emissions from coal- burning power plants be eventually cut by 70-90%, de- pending on the sulfur content of the coal, and that nitro- gen oxide emissions be reduced by about 2 million metric tons per year.

Why are Methane Hydrates interesting

Methane hydrates in the marine environment are a po- tential energy resource with approximately twice as much energy as all the known natural gas, oil, and coal deposits on Earth.

Crude Oil and Natural Gas

Most geologists accept the hypothesis that crude oil (petroleum) and natural gas are derived from organic materials (mostly plants) that were buried with marine or lake sediments in what are known as depositional basins. Oil and gas are found primarily along geologically young tectonic belts at plate boundaries, where large depositional basins are more likely to occur.

strip mining

Over half of the coal mining in the United States is done by strip mining, a surface mining process in which the overlying layer of soil and rock is stripped off to reach the coal. The practice of strip mining started in the late 19th century and has steadily increased because it tends to be cheaper and easier than underground mining.

Petroleum (Crude Oil) Production

Production wells in an oil field recover oil through both primary and enhanced methods. Primary production in- volves simply pumping the oil from wells, but this meth- od can recover only about 25% of the petroleum in the reservoir. To increase the amount of oil recovered to about 60%, enhanced methods are used.

Oil in the 21st Century

Recent estimates of proven oil reserves suggest that, at present production rates, oil and natural gas will last for a few decades.

The Environmental Effects of Oil and Natural Gas

Recovering, refining, and using oil and to a lesser ex- tent natural gas—cause well-known, documented environmental problems, such as air and water pollution, acid rain, and global warming. People have benefited in many ways from abundant, inexpensive energy, but at a price to the global environment and human health.

Tar sands

Sedimentary rocks or sands impregnated with tar oil, asphalt, or bitumen. Petroleum cannot be re- covered from tar sands by pumping wells or other usual commercial methods because the oil is too viscous (thick) to flow easily. Oil in tar sands is recovered by first mining the sands—which are very difficult to remove—and then washing the oil out with hot water. It takes about two tons of tar sand to produce one barrel of oil.

Peak Oil

The point at which half the total known oil supply is used up

Coal-Bed Methane

The processes responsible for the formation of coal include partial decomposition of plants buried by sediments that slowly convert the organic material to coal. This process also releases a lot of methane (natural gas) that is stored within the coal.

Source Rock

The source material, or source rock, for oil and gas is fine-grained (less than 1/16 mm, or 0.0025 in., in diam- eter), organic-rich sediment buried to a depth of at least 500 m (1,640 ft), where it is subjected to increased heat and pressure. The elevated temperature and pressure initi- ate the chemical transformation of the sediment's organic material into oil and gas. The pressure compresses the sediment; this, along with the elevated temperature in the source rock, initiates the upward migration of the oil and gas, which are relatively light, to a lower-pressure envi- ronment (known as the reservoir rock). The reservoir rock is coarser-grained and relatively porous (it has more and larger spaces between the grains). Sandstone and porous limestone, which have a relatively high proportion (about 30%) of empty space in which to store oil and gas, are common reservoir rocks.

The Future of Coal

There is serious concern about burning that coal. Giant power plants that burn coal as a fuel to produce electricity in the United States are responsible for about 70% of the total emissions of sulfur dioxide, 30% of the nitrogen ox- ides, and 35% of the carbon dioxide.

underground mining

Underground mining accounts for approximately 40% of the coal mined in the United States and poses special risks both for miners and for the environment. The dangers to miners have been well documented over the years in news stories, books, and films.

Why are Methane Hydrates hard to reach

Unfortunately, mining methane hydrates will be a difficult task, at least for the near future. The hydrates tend to be found along the lower parts of the continental slopes, where water is often deeper than 1 km. The deposits themselves extend into the seafloor sediments another few hundred meters. Drilling rigs have more prob- lems operating safely at these depths, and developing a way to produce the gas and transport it to land will be challenging.

Natural Gas

We have only begun to seriously search for natural gas and to utilize this resource to its full potential. One reason for the slow start is that natural gas is transported primarily by pipelines, and only in the last few decades have these pipe- lines been constructed in large numbers.

Examples of fossil fuels

coal, crude oil, natural gas