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The occurrence of [http://www.glossary.oilfield.slb.com/en/Terms/n/natural_gas.aspx natural gas] in coal beds has been recognized for hundreds of years, because it is commonly released from the coal and occasionally causes deadly explosions in underground coal mines. [[Coal]] is the most abundant energy source in the Earth, and it should therefore be expected that large volumes of gas, generally called coalbed methane (CBM), should be present in coal deposits throughout the world, providing an enormous potential energy resource.<ref name=Bibleretal_1998>Bibler, C. J., J. S. Marshall, and R. C. Pilcher, 1998, [http://www.sciencedirect.com/science/article/pii/S0166516297000384 Status of worldwide coal mine methane emissions and use]: International Journal of Coal Geology, v. 35, nos. 1-4, p. 283-310.</ref>
The occurrence of [[natural gas]] in coal beds has been recognized for hundreds of years, because it is commonly released from the coal and occasionally causes deadly explosions in underground coal mines. [[Coal]] is the most abundant energy source in the Earth, and it should therefore be expected that large volumes of gas, generally called coalbed methane (CBM), should be present in coal deposits throughout the world, providing an enormous potential energy resource.<ref name=Bibleretal_1998>Bibler, C. J., J. S. Marshall, and R. C. Pilcher, 1998, [http://www.sciencedirect.com/science/article/pii/S0166516297000384 Status of worldwide coal mine methane emissions and use]: International Journal of Coal Geology, v. 35, nos. 1-4, p. 283-310.</ref>
Coalbed methane is generated during the coalification process, and most of it (98%) is found adsorbed in the coal, which is a [[Wikipedia:Microporous material|microporous]] solid with large internal surface areas in the [[http://www.britannica.com/EBchecked/topic/369508/matrix matrix] pore structure that can adsorb very large amounts of gas. Lesser amounts can occur as free gas in [[fracture]]s (called [http://eis.uow.edu.au/outburst/html/Factors/cleat_joints_pg1.html cleats]) and large pores, and/or dissolved in the groundwater present in pores and fractures; coal serves as both the [[Source rock|source]] and the [[reservoir]] rock for the coalbed methane.
Coalbed methane is generated during the coalification process, and most of it (98%) is found adsorbed in the coal, which is a [[microporous]] solid with large internal surface areas in the matrix pore structure that can adsorb very large amounts of gas. Lesser amounts can occur as free gas in [[fracture]]s (called [http://eis.uow.edu.au/outburst/html/Factors/cleat_joints_pg1.html cleats]) and large pores, and/or dissolved in the groundwater present in pores and fractures; coal serves as both the [[Source rock|source]] and the [[reservoir]] rock for the coalbed methane.
Gas produced from coal beds is composed mainly of [http://scifun.chem.wisc.edu/chemweek/methane/methane.html methane] (in excess of 95%) and very minor amounts of heavier hydrocarbons (mostly [http://pubchem.ncbi.nlm.nih.gov/rest/chemical/ethane ethane] and [http://www.propanecouncil.org/council/what-is-propane/ propane]), nitrogen, and carbon dioxide (CO<sub>2</sub>).
Gas produced from coal beds is composed mainly of [[methane]] (in excess of 95%) and very minor amounts of heavier hydrocarbons (mostly [[ethane]] and [[propane]]), nitrogen, and carbon dioxide (CO<sub>2</sub>).
The gas content of coal beds generally varies with the rank of the coal and its depth of burial; the higher the coal rank and the greater the depth, and the resulting pressure to which the coal has been subjected, the greater its potential gas content. For a given coal rank, the adsorbed gas content increases with increasing pressure and decreases with increasing temperature.
The gas content of coal beds generally varies with the rank of the coal and its depth of burial; the higher the coal rank and the greater the depth, and the resulting pressure to which the coal has been subjected, the greater its potential gas content. For a given coal rank, the adsorbed gas content increases with increasing pressure and decreases with increasing temperature.
* [[Historical sources of energy]]
* [[Historical sources of energy]]
* [[Natural-gas liquids]]
* [[Natural-gas liquids]]
* [[Natural gas]]
* [[Natural gas: history and forecast]]
* [[Natural gas occurrence]]
* [[Natural gas occurrence]]