About Coalbed Methane
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How CBM is Created
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. Like natural gas from conventional sources, CBM is “sweet” not “sour” as it doesn’t contain hydrogen sulphide. CBM is an unconventional gas as the gas is contained in difficult-to-produce reservoirs, which require special completion, stimulation and/or production techniques to achieve economic production
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. In some cases the wells are drilled horizontally and 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.
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.
Approximately 95 per cent of the coalbed methane wells drilled in Alberta have targeted the thinner coal seams in the Horseshoe Canyon (gas in place 71 Tcf) and Belly River coal zones along the Calgary-Red Deer corridor. Wells targeting these seams tend to produce gas with little or no water. The depth range of these coals is 200 to 800 m.
Most of the remaining CBM wells drilled have targeted the deeper 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.
The Energy Resources Conservation Board/Alberta Geological Survey completed a report on the Ardley-Paskapoo entitled “Preliminary Investigation of Potential, Natural Hydraulic Pathways between the Scollard and Paskapoo Formations in Alberta: Implications for Coalbed Methane Production”. The report
, supports improved understanding of aquifer systems.
