How Methane in Natural Gas is Formed

Published: 12th October 2007
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Natural gas is a fossil fuel found underneath the ground in large pockets. These pockets are located inside porous rock. The principal chemical ingredient of natural gas is methane which is considered the cleanest fossil fuel because of its clean-burning qualities. Small amounts of other gases also are contained in natural gas, including ethane, propane, butane and pentane. The natural gas delivered to our homes is almost pure methane because the other gases are removed.

The chemical makeup of methane is one molecule of carbon and four molecules of hydrogen. It's odorless and colorless and lighter than air. Methane is a gas made by anaerobic bacteria. Anaerobic bacteria are bacteria that can live without oxygen, unlike green plants. Millions of years ago when there was very little oxygen in the earth's atmosphere the anaerobic bacteria could survive. Today, the air we breathe is about 75% nitrogen and 25% oxygen. However, four billion years ago, no oxygen was present. Earth's atmosphere was a combination of carbon dioxide, nitrogen and hydrogen sulfide, uninhabitable by humans.

The anaerobic bacteria were the earth's first inhabitants. These bacteria pumped large amounts of methane into earth's atmosphere which changed it significantly. About 2.5 billion years ago, blue-green algae developed in the oceans and emitted large amounts of oxygen into the air. The oxygen reacted with methane, dissipating most of it. When the methane in the atmosphere dissipated most of the anaerobic bacteria were killed. Blue-green algae became the dominant life form and the Earth's atmosphere got free oxygen. Aerobic bacteria became predominant which made multicellular life, including human beings, possible.

Today, there are three theories about how methane is formed. The three main theories as to the origins of methane are called: thermogenic, biogenic and abiogenic. The thermogenic theory says that methane is formed when the remains of plants and animals are compressed deep underground at high pressure for a long period of time. The plants and animals pile on top of each other and get covered with mud and other sediments. Eventually enough pressure is put on the plants and animals to compress it. The high temperatures deep underground in combination with this compression breaks down the carbon molecules. The deeper in the ground these compost piles are the more natural gas is formed. Closer to the surface the deposits contain more oil than natural gas because oil contains more carbon molecules than natural gas and the high temperatures aren't there to break the carbon down.

The biogenic theory states that methane is created when organic matter is transformed by tiny microorganisms. These microorganisms are found in the intestines of most animals and in areas close to earth's surface where oxygen is not available. A lot of the methane produced close to the surface dissipates into the atmosphere. It also is trapped underground and can then be recovered as natural gas. Landfills are examples of biogenic methane. The waste in the landfill decomposes producing methane and we are just starting to develop ways to recover this methane for our energy needs.

The abiogenic theory has to do with the hydrogen gases and carbon molecules that exist deep under the crust of the earth. These gases rise up toward the surface, interacting with other minerals causing reactions that change their chemical nature. This combined with the high pressure as they get closer to the surface forms methane deposits like the thermogenic methane. The thermogenic theory is by far the theory accepted by most researchers.

Mickey Horn is the Executive VP of Investor Relations of Western Pipeline Corporation. Western Pipeline Corp specializes in identifying, acquiring and developing existing, producing reserves on behalf of its individual clients.

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