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Coal Formation Petroleum and Natural Gas  

Introduction to
Nonrenewable Resources

Energy is the ability to do work. Energy is needed to power cars and factories, heat schools and homes, refine metals, and make many of the things we take for granted. Wind, water, the sun, nuclear reaction, coal, petroleum, natural gas, gasohol, the tides, and geothermal steam are some of Earth's energy resources. Some of these resources are renewable, others are nonrenewable. Several of the nonrenewable energy sources are being rapidly exhausted.

Fossil Fuels
Coal Formation

  Coal (Press the green button to see a diagram.)
Coal forms in swampy areas as the result of the decay of plants in the absence of oxygen. Biochemical changes produced by bacteria release oxygen and hydrogen and concentrate carbon. Coal goes through several changes during formation. With increased pressure and time, impurities and moisture are removed. In swamps where coal forms, other sediment, such as sand, clay, and silt, also is deposited. The weight of the sediment compresses the underlying organic matter. During this process, moisture and other materials are squeezed out, leaving a high carbon concentration.

Peat (Press the green button to see a photo)
The first stage in coal formation is material composed of about 75 to 90 percent water plus twigs, leaves, branches, and other plant debris. Although peat itself is not coal, it is an important fuel used in Ireland and the Soviet Union.

 

Lignite (Press the green button to see a photo)
The second stage of coal formation is brown coal composed of compressed woody matter that has lost most of its moisture. It is used for local fuels in homes and industry. Germany uses its lignite to provide synthetic petroleum.

 

Bituminous (Press the green button to see a photo)
The third stage of coal formation is a dense, dark, brittle material that has lost all its moisture and most other impurities. It is ignited easily by a flame. Although bituminous coal is an efficient heating material, it produces a smoky yellow flame, ash, and sulfur compounds when it is burned. Strict emission laws have limited the amount of pollutants industries can release when this coal is burned. Bituminous coal is mined throughout the United States with major fields in the Appalachians, the Great Plains, and the Colorado Plateau.

 

Anthracite (Press the green button to see a photo)
Anthracite, sometimes called "hard coal," is the final stage in coal formation. Lignite coal and bituminous coal are sedimentary rocks. Anthracite is a metamorphic rock. It is found only in areas of mountain building where heat and pressure were great. Anthracite is the cleanest of all coals with the least impurities because it is mostly carbon. It does not produce as much heat as bituminous coal, but it is preferred because it burns cleaner and longer. Anthracite fields occur in northeastern Pennsylvania, Great Britain, and parts of the Soviet Union.

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Fossil Fuels

Petroleum and Natural Gas

Petroleum, or crude oil, and natural gas are important hydrocarbons that are found in nature within pores and fractures of rocks. Oil and gas form over millions of years as the result of the decay of marine organisms. These organisms die and collect on the ocean floor. Sediments such as clay and mud are deposited above these organisms. During burial and compaction, the organic matter becomes heated. Hydrocarbons are formed and are forced out of the source rock into permeable beds such as sandstone.

 

Because oil and gas are not very dense, they migrate upward through the water-saturated rock layers. In some cases, this movement is stopped by overlying impermeable layers of rock such as shale or rock salt and the hydrocarbons are trapped. Then, the oil and natural gas form a reservoir in the porous rock. This type of hydrocarbon accumulation requires a source rock, a reservoir rock, and a cap rock. Most of the world's reservoirs are in sandstone, limestone, and dolomites. Structural traps are related to folds, faults, or salt domes. When an anticline fold that contains hydrocarbons is drilled, the first material encountered is usually natural gas. This gas often is underlain by oil due to density differences. Water is the densest fluid and is found at the bottom of a reservoir.

 

Natural gas was once burned at wells as waste. Now natural gas is a very important fuel because it is the easiest fossil fuel to transport and the cleanest to burn. Although natural gas often occurs with oil, some fields produce only natural gas. Both natural gas and oil supplies are limited, and the cost of using these fuels is rapidly increasing. Every person in the United States uses the equivalent of a barrel of oil every six days, and much of this oil must be imported from the Middle East. In fact, in 1985 the United States imported about seven million barrels of oil each day. Before 1970, a barrel of oil cost $3.00. In 1973-74, the Arab oil embargo caused the price to raise to $12.00 per barrel. In 1985, the price of one barrel was $27.00. (These statistics change and students need to research what it is at the present time.)

 

Secondary recovery methods can be used to increase the amount of crude oil that can be pumped from wells. Presently only about 30 percent of the crude oil in a well can be recovered. However, as oil reserves dwindle, steam, carbon dioxide, and detergents can be used to force out the heavy oil that normally cannot be pumped. Because oil and natural gas are nonrenewable natural resources, each person must take an active part in the conservation of these valuable energy sources. Carpooling, fuel-efficient cars and furnaces, and the lowering of home thermostats during the winter are just a few examples of energy-saving measures. How can you assure adequate supplies of oil and gas for the future?