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КР3 - Natural gas and petroleum - 2008 / 3 рейтинг,устно

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I YEAR, 2TERM, MAY RATING 3 Orally Var.2

Natural gas and petroleum.

Natural gas is a mixture of hydrocarbon gases and vapours found in porous formations in the earth's crust Natural gas is mostly methane. Frequently natural gas occurs with petroleum. Petroleum is a complex mixture of hydrocarbons. This hydrocarbon mixture varies greatly in composition from place to place. The hydrocarbon molecules in petroleum contain from one to more man 50 carbon atoms.

Natural gas and petroleum were probably formed by the decay of plants and animals living millions of years ago. Because of changes in the earth's surface, these plant and animal residues* were trapped in rock formations where they slowly decomposed in the absence of atmospheric oxygen.

Natural gas and petroleum are the most common sources of fuels. But, more importantly, they are a source of hydrocarbon chemical raw materials that is rapidly being used up. Discoveries of new sources of natural gas and petroleum are not keeping up with the amounts being used.

* residue - осадок