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Transcript for The Future of Energy Gases, segment 04 of 13
But natural gas brings new questions to an energy marketplace that has experienced two decades of periodic disruption and confusion. What is natural gas? How does it form? Where do we find it? How much is there? What will it cost? And how will it affect the environment?
Natural gas occurs throughout the Earth's crust. It is not simply a by-product of oil as many of us assume. It is actually a fuel in its own right, different from oil in its occurrence, its properties as a gas, and in its origin.
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Oil occurs mainly at depths less than ten thousand feet and always in association with natural gas. But natural gas occurs to depths of at least forty thousand feet often on its own but also in association with coal and even dissolved in hot brine. Natural gas is forming today in landfills from the breakdown of organic materials and is even found lodged within the crystal structure of ice.
Methane is the main component of natural gas. This simple compound contains less carbon and fewer impurities than coal or oil and burns more cleanly than either. Most importantly, burning natural gas produces less carbon dioxide, a major contributor to the greenhouse effect and potential global warming. Burning natural gas also adds fewer nitrogen compounds and almost no sulfur to the atmosphere, resulting in less of the acid rain and acid fog that are produced from the combustion of oil and coal.
Like oil, natural gas is formed from organic materials contained in rocks. When these rocks are heated slowly in the Earth or more rapidly in a test tube, the organic material breaks down, forming oil and natural gas. Unlike oil, however, natural gas is also produced from organic matter by the work of archibacteria. These organisms occur in the Earth almost everywhere that oxygen is absent, at least to temperatures of ninety-seven degrees Centigrade. Most oil and natural gas originate from the decomposition of plant materials that accumulate in lakes, marshes, and along the shores of oceans.
At shallow depths, archis produce methane from these plant remains, sometimes in large amounts. As the sediment layers are buried, temperature rises. At depths of about two miles heat begins to break the chemical bonds of organic molecules, forming oil and natural gas. As burial continues, temperature rises still higher, oil becomes unstable, and only natural gas forms. Pushed by pressure and buoyancy, the oil and natural gas travel from their source, moving through the Earth at perhaps a few inches per year. Some is trapped by dense layers of impermeable rock called seethe. If enough pore space is available beneath the seethe, a rich deposit of oil and gas may develop.
Most oil and gas never gets trapped. Some remains in the source while the rest moves to the surface. Natural gas enters the atmosphere, and oil turns to tar or is decomposed by microorganisms.
Much of the natural gas we have found was discovered during the intense ongoing search for oil. This oil-associated natural gas is known as a conventional resource because it can be tapped using standard techniques. Recent estimates by the National Petroleum Council show that we have at least seven hundred and seventy-five trillion cubic feet of conventional natural gas available to us in the United States, forty years' supply if we burn it at the rate we do today.