Changes

Some of the sources of natural gas labeled unconventional in the past have produced gas profitably in the United States for at least a decade or two and will undoubtedly become major sources of energy in the decades to come. Not only in the United States but in many other countries of the world, such unconventional sources of natural gas are known to occur, and although they are not given serious recognition now, they will certainly be developed sometime in the future. Foremost in this category of former unconventional sources of natural gas in the United States are gas in coal beds (the [[coalbed methane]]), gas in low-permeability sandstones ([[tight sands]]), [[basin-centered gas]] accumulations, and gas in organic black shales (also known as fractured shales). As of 2002, they contributed 26% of the total United States gas production.<ref name=LawandCurtis_2002>Law, B. E., and J. B. Curtis, 2002, [http://archives.datapages.com/data/bulletns/2002/11nov/1851/1851.htm Introduction to unconventional petroleum systems]: AAPG Bulletin, v. 86, no. 11, p. 1851-1852.</ref>

Some of the sources of natural gas labeled unconventional in the past have produced gas profitably in the United States for at least a decade or two and will undoubtedly become major sources of energy in the decades to come. Not only in the United States but in many other countries of the world, such unconventional sources of natural gas are known to occur, and although they are not given serious recognition now, they will certainly be developed sometime in the future. Foremost in this category of former unconventional sources of natural gas in the United States are gas in coal beds (the [[coalbed methane]]), gas in low-permeability sandstones ([[tight sands]]), [[basin-centered gas]] accumulations, and gas in organic black shales (also known as fractured shales). As of 2002, they contributed 26% of the total United States gas production.<ref name=LawandCurtis_2002>Law, B. E., and J. B. Curtis, 2002, [http://archives.datapages.com/data/bulletns/2002/11nov/1851/1851.htm Introduction to unconventional petroleum systems]: AAPG Bulletin, v. 86, no. 11, p. 1851-1852.</ref>

Coalbed methane, which not too long ago was considered an unconventional type of gas accumulation (and the cause of deadly accidents in underground coal mines), is now being produced profitably in several basins in the United States (about 7% of the total United States natural-gas production) and in Australia and is being investigated in other parts of the world. Natural gas from tight-sand reservoirs is also becoming a substantial part of the total natural gas produced in the United States. Lesser production has been obtained for many years from organic black shales and from basin-centered reservoirs. Production of the natural gas in [[Gas hydrates|methane hydrates]] and in solution in [http://www.glossary.oilfield.slb.com/en/Terms/g/geopressure.aspx geopressured] formation waters will probably not be economically viable for many years, if ever. These last two occurrences of natural gas may be better called speculative.

Coalbed methane, which not too long ago was considered an unconventional type of gas accumulation (and the cause of deadly accidents in underground coal mines), is now being produced profitably in several basins in the United States (about 7% of the total United States natural-gas production) and in Australia and is being investigated in other parts of the world. Natural gas from tight-sand reservoirs is also becoming a substantial part of the total natural gas produced in the United States. Lesser production has been obtained for many years from organic black shales and from basin-centered reservoirs. Production of the natural gas in [[Gas hydrates|methane hydrates]] and in solution in [[geopressure]]d formation waters will probably not be economically viable for many years, if ever. These last two occurrences of natural gas may be better called speculative.

==See also==

==See also==