Characterising Hydrogeological Conditions to a Depth of 1 km in West-Central Alberta

Unconventional shale-gas plays in west-central Alberta require approximately 30000 m3 of water per well for hydraulic fracturing, which is sourced from surface water and shallow groundwater during the early development stage. However, shallow groundwater availability varies widely and will not be reliable when industry transitions to commercial production. Non-saline groundwater deeper than typical domestic and agricultural uses is considered a potential source, but hydrogeological information is sparse. As part of evaluating Alberta’s groundwater inventory, the Alberta Geological Survey is completing a hydrogeological project for a 22000 km2 region in the west-central part of the province. Regional mapping of total dissolved solids (TDS), opportunistic isotopic sampling (3H, SF6, 4He), and 3D analysis of net-to-gross sandstone ratio begin to characterize deep groundwater. Geological characterization of the uppermost bedrock unit (Paskapoo Fm) shows the unit to be highly heterogeneous with sandstone bodies embedded within a dominantly siltstone and mudstone formation. Groundwater in the Paskapoo Fm has TDS <800 mg/L, and 3H and SF6 concentrations with an apparent age of 30 to 50 years. An underlying bedrock unit (Wapiti Fm) was found to have an upper portion dominated by siltstone and mudstone, and a lower portion with more widespread sandstone. In the Wapiti Fm, TDS varies from 600 to 8000 mg/L, spanning the important saline threshold (4000 mg/L) in Alberta. At one location in the Wapiti Fm where TDS is 1700 mg/L, elevated 4He concentration was found, corresponding to an apparent age of about 135000 years. This study suggests that bedrock units may provide sufficient vertical connectivity to promote circulation of non-saline water to depths of nearly 1 km, and the potential for a confluence of regional flow paths. Although sparse, these data contribute to an understanding of regional water resources and the potential of deep groundwater sources to support unconventional shale-gas in Alberta.