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What is coalbed methane?

  Mar 18, 2017

What is coalbed methane?

Coalbed methane is a form of natural gas extracted from coal beds. The term refers to methane adsorbed into the solid matrix of the coal. It is called 'sweet gas' because of its lack of hydrogen sulphide. The presence of this gas is well known from its occurrence in underground coal mining, where it presents a serious safety risk. The methane is usually held in place by water pressure. Methane, CH4, is a naturally occurring gas; it is the major component (95 percent) of natural gas. It can be produced in a variety of ways. For example, methane is produced during the natural coalification process, when organic matter such as trees or vegetation is quickly buried and then heated. Methane can also be produced by farming and ranching activities or as a by-product of industrial processes. Methane is a greenhouse gas that remains in the atmosphere for up to 15 years, and it is also a relatively inexpensive, clean burning fuel.

Where is coalbed methane found?
Coalbed methane is associated with coal deposits, and is found in coal seams. In the past, the gas was the cause of numerous explosions in underground mines. More recently, the gas has been vented to the surface from underground mines. It is only during the last twenty-five years that it was realized that coalbed methane could be used as a resource. Various basins in the Rocky Mountains hold much of this country's coalbed methane resources.

How is coalbed methane extracted from coal?
When water is removed from a coal seam, it lowers the reservoir pressure. Methane that was held in place by water pressure tends to follow the water as it is pumped to the surface, where it is captured and transported through pipelines to storage facilities or shipped. This relatively inexpensive and straightforward procedure has made coalbed methane a useful, easily accessible form of energy.

How does water extraction affect local aquifers?
Local aquifers may or may not be affected, depending on the local geology, but there is usually some drawdown measured. Various agencies now monitor water in the affected areas to learn more about this process.

What is the environmental cost of coalbed methane?
Coalbed methane production results in changes to the land, to surface water, and to ground-water systems. These changes should be monitored and managed in order to reduce their impact. Environmental Impact Statements have been completed, and although they are being challenged, they remain a starting point. With care, it seems that the environmental costs of coalbed methane can be reduced.

What is the environmental benefit of coalbed methane?
Coalbed methane is produced domestically, reducing our need to import energy. Geologists are aware of the depositional environments that can produce coalbed methane, reducing the cost of extensive exploration. And most importantly, methane is a relatively clean-burning source of energy, much cleaner than coal. All of these factors combine to make coalbed methane a locally-produced, affordable source of energy.

What is Underground Coal Gasification (UCG)?
Coal is the major source of energy all over the world including India. However, it is not technically feasible or economically viable to mine all coal resources and this is where UCG (underground coal gasification) finds its usefulness. UCG has been practiced, though off and on, since the last 50 years by almost all major coal producing countries but it could never become the major energy source. Availability of large amount of cheap natural gas, the danger of contamination of underground water, non-availability of suitable drilling technology, and failure to administer proper control over gasification process are some of the reasons. However, with the efforts put in by many countries over the years, the technology of UCG has matured for commercial application. 

In India the experience of UCG is minimal. However, many deeper coal seams and deeper lignite deposits not economical to mine by conventional mining techniques are good candidates for UCG. Large number of abandoned mines and some shallow coal deposits with difficult geo-mining conditions can use UCG gainfully. Cabinet has approved a policy framework for development of Underground Coal Gasification (UCG) in coal and lignite bearing areas in the country.