Title: Assessment of Unconventional Gas Resources of the Western Canada Sedimentary Basin; Mannville Fm and Equivalents a More Promising CBM Target?
Speakers: Brian McKinstry and Garth Sloan, GTI E&P Services Canada Inc.
Date: November 15, 2002
Publication: The Outcrop, November 2002, p. 4-5
As part of an on-going industry-funded study of unconventional gas resources of the Western Canada Sedimentary Basin (WCSB), detailed work has been carried out over the past year in assessing the coalbed methane (CBM) potential of the coals of the lower Cretaceous age Upper Mannville Formation and equivalents. This investigation has included core examination, case studies and detailed localized geological analysis. The intent has been to ascertain the relative prospectivity of these coals with respect to other coal-bearing intervals within the basin and identify specific play types that may assist industry in their exploration efforts.
Within the Upper Mannville Formation, it has been well recognized that both coal seam net thickness and rank of coal increase downdip toward the Rocky Mountain thrust belt. However, with increasing depth of cover, reduced permeability becomes an increasing issue. At relatively shallow depth of cover (less than 700 meters), seam development is often thin and sporadic while rank of coal suggests biogenic rather than thermogenic gas production processes will prevail. Effort has been made to investigate coal thickness anomalies at depth of cover that would offer a balance between these opposing factors.
Recent CBM exploration efforts have indicated that measured permeability in Mannville coals at moderate depth of cover may offer economic potential. Preliminary data suggests that level of gas saturation and the nature of gas composition (low CO2, significant C2+ components) may make this zone an excellent CBM target. The oily nature of the coal, perhaps an outcome of the basin-wide petroleum migration updip towards the northeast Alberta oil sand deposits, suggests minimal water production should be expected. Additional play opportunities are also offered in the deep basin where overpressuring may stimulate CBM production; and the overthrust belt where high rank coals have been emplaced at relatively shallow depths in discrete thrust sheets.