Petrographic Variability of Horseshoe Canyon Coals in the Central Alberta Plains

David B. Moore, Murray Rodgers, David Bilenduke, and Darren Tisdale
Trident Exploration Corp, Calgary, AB

To date, dry coals of the Upper Cretaceous Horseshoe Canyon Formation, Edmonton Group, produce the only commercial CBM in Canada. These coals were deposited during the Upper Cretaceous along the eastern margin of the interior seaway in settings ranging from fluvial to coastal plainsto marginal marine. A detailed petrographic study was conducted by Trident as a component of a regional exploration methodology. These subbituminous to high volatile bituminous coals reveal considerable variation in rank with vitrinite reflectance of 0.42 to 0.62 (% Ro). In other CBM basins coal rank has been shown to have a direct relationship on coal seam gas content and ultimately gas production.

The Horseshoe Canyon coals also display significant variation in terms of coal composition. Maceral analysis of coal from approximately 25 wells over an area from Township 25, Range 16W4M to Township 42 Range 26W4M reveals important differences in vitrinite content, vitrinite-inertinite ratios, as well as variation in concentrations of individual macerals which suggest differences in depositional environments. These elements are expected to have an impact on well production performance.

Accessory minerals, such as pyrite, siderite, gypsum-anhydrite and clay minerals also reveal differences in environment and diagenetic histories. Some coals reveal ancient fluid flows, while others indicate they have been dry for most of their post-depositional history.

Maps showing coal rank and composition can be used in high grading CBM exploration trends within the Horseshoe Canyon Formation.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005