by Patrick Coyle

Created on: March 17, 2009

Methane hydrates, essentially frozen methane gas and water, are a double edge sword. They have the potential for being a clean energy source. They are, unfortunately, an essentially un-renewable fuel and a source for new' atmospheric carbon dioxide if burned. Even if left un-mined, they are a potentially potent greenhouse gas that could accelerate global warming.

Methane Sources

The methane gas portion of the hydrate comes from two sources. The first source is produced by decomposition of hydrocarbons (coal and oil) buried deep beneath the earth's surface. Since that decomposition is driven by heat this is known as the thermogenic methane. The second source is from biological activity in ocean sediments. Here anaerobic micro-organisms consume dead plants and animals and produce methane as a waste byproduct. The methane gas produced by these biological organisms is collectively called biogenic methane.

As the methane gas rises from either source some of it becomes trapped in hydrate stability zones. These are areas where the methane can mix with water in the proper combination of temperature and pressure. In these conditions the water and methane freeze to form a methane hydrate. This stable crystalline material will stay in this solid form as long as the temperature and pressure remain within the critical range. Decreasing pressure or increasing temperature will cause the material to melt and disassociate into methane gas and liquid water.

According to a recent report to Congress the Energy Department conservatively estimates that the volume of methane hydrates exceeds the known reserves of all other hydrocarbon fuels combined. This makes this material valuable as a potential fuel source, especially since the methane gas is not contaminated with the sulfur compounds found in most liquid fossil fuels and coal.

Finding Methane Hydrates

Because of the temperature and pressure requirements for forming and maintaining methane hydrates they are found in two locations. On land they can only exist in areas where the ground is always frozen (permafrost) and layers of impermeable rocks trap and concentrate the rising thermogenic methane gas. Thus far methane hydrate deposits have been found in the far north in Russia, Canada and Alaska. Presumably deposits could be found in Antarctica.

In the oceans methane hydrates are normally found out beyond the continental shelf in the deeper waters on the Continental slopes. Here the biogenic source of the material is close to the surface

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