Basin-Scale Geology and Hydrogeology of Coalbed-Methane Bearing Strata in Rocky Mountain Sedimentary Basins

Worldwide resources of methane trapped within the coal porous system are greater than the collective reserves of all known conventional gas fields. However, only in very few places, primarily in the United States, has this energy source been commercially tapped. Except for the Black Warrior basin in Alabama, all major basins in the United States where coalbed methane is produced or have producibility potential are foreland Rocky Mountain sedimentary basins. The coal beds in these basins are found in Upper Cretaceous and Tertiary strata. Canada also has abundant coal resources, particularly in the Upper Cretaceous-Tertiary succession of the Rocky Mountain foreland of the Alberta basin. Coalbed methane resource estimates for the Alberta basin vary between 300 and 540 Tcf. Coalbed methane producibility depends in an interrelated manner on geological factors, such as tectonic, structural and depositional setting, on coal distribution and properties, such as rank and gas content, and on hydrogeological factors, such as permeability and flow of formation waters. Several studies of coalbed methane potential and producibility in US Rocky Mountain foreland basins address is a comprehensive, multi-disciplinary manner all factors relating to coalbed methane potential and producibility. No comprehensive study exists to date for Canadian coalbed methane resources. An overview of the geological and coal characteristics of coal-bearing basins in the US and Canada was recently completed by the Geological Survey of Canada (GSC). However, no review of the hydrogeology of the coal-bearing strata and of the effect of groundwater flow on coalbed methane migration, accumulation and producibility was undertaken. Together with the GSC report, this review should provide the regional-scale information and understanding of the various geological and hydrogeological conditions in these basins and how they affect coalbed methane producibility. Particular attention is given to the Alberta basin, as it has probably the largest untapped resources.