Coalbed Methane in Alberta: History, Geology, Production and Current Activity

This 48-page presentation was given to the Mineral Exploration Group (MEG) in Calgary on December 3, 2003. The talk outlined general coal and coalbed methane (CBM) concepts, including coal geology, gas generation and migration in coal and the role of permeability in CBM production. CBM development history in the USA and Canada were compared. The coal geology and CBM potential of Alberta was presented for each of the four major coal-bearing formations, along with maximum gas-in-place estimates for the province. Current CBM activity, the presence of both wet and dry CBM wells, and CBM development issues were presented.

Abstract

Alberta has vast coal resources that are a potential source of coalbed methane. Exploration and research are currently underway in the province to quantify gas potential, identify key geological factors that maximize CBM potential, and identify the 'most favourable' areas for CBM production potential.

Alberta contains substantial coal resources in the Plains and Foothills. Potential coalbed methane targets exist in the Scollard Formation (Ardley coal zone), Horseshoe Canyon Formation (Carbon-Thompson, Drumheller coal zones), Belly River Group (Lethbridge, Taber, McKay coal zones) and the Mannville Group within the Plains, and in the Kootenay, Gething, Gates, Brazeau and Coalspur coal zones of the Foothills/Mountains. Maximum gas-in-place for all of the coal in Alberta is estimated to be 1.42 x 10¹³m³ (500 tcf). Although this number is large, the actual amount able to be produced remains unknown, in part due to limited data on gas concentration, permeability and production constraints.

Unlike conventional gas reservoirs, methane is adsorbed onto the coal seam 'reservoir.' The coal is both the reservoir and source rock for methane. Seam pressure must usually be reduced to allow methane to migrate from the coal matrix to the wellbore, sometimes achieved by removing fluids from the reservoir.

At present there are in excess of 180 CBM wells in production, with over 500 CBM 'test wells' identified in the province. A major challenge in CBM exploration is locating coals with adequate permeability to facilitate production. CBM wells tend to be relatively low gas volume producers, and a well density tighter than that of conventional wells is commonly required to allow reservoir depressurization and economic production.

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