About Coalbed Methane

When plant material such as roots, bark, and wood are deposited in swamps or swampy lakes, they undergo bacterial and chemical changes to make peat deposits. As the peat is buried deeper, under layers of sand and mud, over millions of years, it changes to brown coal, then bituminous coal, and eventually hard, anthracite coal (coalification process).

As the coal is formed, the decomposing organic material produces methane gas, as well as nitrogen, carbon dioxide, and other gases. The burial process puts pressure on the coal, which keeps much of the gas in the coal.

Characteristics of CBM

• the natural gas found in coal is "sweet" not "sour", as it does not contain hydrogen sulphide;
• it is generally methane with small amounts of carbon dioxide and nitrogen;
• it is generally of near-pipeline quality when produced and requires minimal processing; and,
• it is generally produced at lower pressures than conventional natural gas.

An unconventional gas

CBM is called an unconventional gas because the coal acts as both the source of the gas and the storage reservoir. Most of the CBM is attached to or "adsorbed" on the coal surfaces and it may also be trapped in the coal fractures, which tend to have low permeability.

Conventional natural gas is gas that is created from organic-rich sediments and moves into a different rock's pore space. Gas released from coal beds can also move into adjacent rocks. If this occurs, the gas is no longer considered CBM.

CBM and other unconventional sources of natural gas (i.e. shale gas, gas in tight sands, gas hydrates) generally are less economically viable compared to conventional gas. Over time, technological breakthroughs could reduce production costs.

Extraction

CBM is extracted by drilling a well into a coal seam using similar techniques used for other gas wells. The sides of the well are "cased" with cemented steel pipe. Usually, small holes, called perforations, are then made in the wall of the casing to let the CBM flow through into the well bore and up the casing to the surface. The coal seams are often stimulated or "fractured" to make the CBM flow more freely.

Standard drilling and extraction technology is used or adapted as conditions require. After the gas is extracted, it may be compressed before it is piped to market.

Potential in Alberta

The Alberta Geological Survey estimates there may be up to 500 Trillion cubic feet of natural gas in Alberta's coals. It is not known how much of this gas may be economic to produce. As more information becomes available the production potential will become clearer.

• Cross-section of Coal-bearing Formations Across Alberta

Current drilling activity

In 2000, there were about 50 CBM wells drilled in Alberta.   As of December 31, 2006, there were a total of 10,723 CBM wells in Alberta, which includes all wells completed in coals plus any wells licensed for CBM which were finished drilling by that date.  A total of 2943 CBM wells were added in 2006.

Of the total 10,723 CBM wells, 6905 had produced or were producing by December 31, 2006.  These wells may have produced only from coals or from a combination of coals and other gas zones.

ERCB Well List

• CBM Well List (as of 2003)                                  
• CBM Well List (as of 2004)
• CBM Well List (as of 2005)
• CBM Well List (as of 2006)

The majority of coalbed methane development is taking place in the dry Horseshoe Canyon and Belly River coals of south-central Alberta. 

Alberta's geology - learning from projects in Alberta

As more wells are drilled in Alberta, we are getting valuable information about the potential and characteristics of associated water production, and a clearer picture of Alberta's geology.

Over 90 percent of the wells drilled at the end of 2006 had targeted thinner coal seams in the Horseshoe Canyon (gas in place 71 Tcf) and Belly River coal zones.  Wells targeting these seams tend to produce gas with little or no water.  The depth range of these coals is 200 to 800 m.

About eight percent of the projects have targeted the Mannville coals (gas in place - 239 Tcf).  These coals tend to be thicker, deeper, and more continuous with substantial saline (salt) water production.  The depth range of these coals is 900 to 1,500 m.

Less than one percent of wells have been completed in the shallower Ardley coals of the Scollard Formation (gas in place - 57 Tcf).  These coals can produce varying quantities and qualities both saline and non-saline water as well as no water.  The depth range of these coals is 350 to 700 m.

Less than one per cent of the CBM wells were drilled to test production from Kootenay coals, which generally produce small volumes of water.