Earth Sciences Report 2007-06

Author(s) Date 2007-06-30

Two major aspects of economic and environmental interest in Alberta - coalbed methane (CBM) exploration and development and CO2 injection in coal strata to increase the enhanced CBM recovery (CO2-ECBM)�motivated the present study. The economic importance of CBM in the Ardley Coal Zone, associated with the emerging issue of potential CO2 storage in coals have led the Alberta Geological Survey to undertake this project to better understand the geological reservoir conditions within the Edson CBM exploration block.

The present study focuses on the following: a. the development of a sequence stratigraphic model, which allows a realistic coal correlation in the Edson CBM exploration block; b. Ardley Coal Zone reservoir characterization, and c. geometry of the adjacent sandstone channels and their connectivity with the coal reservoirs units.

The report is structured in three parts: the first part presents an overview based on new data, of the Battle-Scollard-Paskapoo succession in the Edson CBM exploration block; the second part focuses on the Ardley Coal Zone reservoir characterization, where new lithologic and stratigraphic data associated with publicly available formation-pressure and water chemistry data have been systematically analysed, delineating the coal properties, coal zone internal structure, hydrogeology and fracture pattern, coal tonnage and gas-in-place estimation per coal subunit; and the third part defines the fluvial channels within Scollard-basal Paskapoo succession and the coal-channels architecture in the Edson block, emphasizing the potential pathways of geo-fluid migration.

This study recognizes five fluvial sequences in the Edson block. These are interpreted as dynamic responses to cyclic slow-thrusting tectonic stages followed by isostatic rebounding, similar to the model deciphered for the Pembina coal sub-basin (Pana, 2006). The depositional environments favourable to coal accumulation migrated from the east-central part of the Edson coal sub-basin at the beginning of coal deposition time ('N' coal subzone) to the west-central ('Ml' and 'Mu' coal subzones) and strongly to the southwest at the end of the Ardley deposition time ('S' coal subzone). The coal subzones ('N,' Ml,' 'Mu' and 'S') can be considered individual reservoirs due to their particular geometry and sealing characteristics. The examined drillcores have shown that the 'banded coal' category is the dominant type of coal in the Edson block. Cleats free of calcite infilling are dominant. Vitrinite reflectance is 0.54�0.59% within the onset of hydrocarbon generation. Interpretation of the fracture system suggests two areas of potential 'two-face-cleats systems' northwest and southeast of the Athabasca River. Differential compaction of the underlying sediments locally possibly amplified existing cleats or generated additional fractures at the contact of the coal seams with the sandstone channels. Outcrop of the Paskapoo sandstone channels shows the presence of post-lower Paleocene fractures. The Scollard-Paskapoo succession in the Edson exploration block is considered an unconfined aquifer, based on the formation-pressure and water salinity analyzed data. Ardley Coal Zone total gas-in-place is 528 x 109 m3 in the Edson block. Each of the lower three coal subzones ('N,' 'Ml' and 'Mu') presents a consistent estimative content of gas of 110-222 x109m3, except the uppermost coal subunit ,'S,' which has only 31 x109 m3, mainly due to the substantial erosion of the coal strata. The sandstone channels and the underlying coal seams show direct stratigraphic contact in some locations, which may allow the gas to migrate under specific reservoir conditions. Both coal and sandstone types of reservoirs have inherent permeability. The stratigraphic contact of the two types of reservoirs infers reservoir connectivity and can be considered potential pathways for gas migration in the CO2-ECBM strategy.

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Pana, C. (2007): Edson CBM exploration block-Alberta, Ardley Coal Zone characterization and sandstone channels geometry; Alberta Energy and Utilities Board, EUB/AGS Earth Sciences Report 2007-06, 124 p.