Baseline Hydrogeological Regime at the Intermediate Scale, AOSTRA Underground Test Facility

This report presents the baseline hydrogeological regime of formation waters in the Phanerozoic sedimentary succession in an area of approximately 4000 km² (5x8 townships) surrounding the Alberta Oil Sands Technology and Research Authority (AOSTRA) Underground Test Facility (UTF) near Fort McMurray in northeast Alberta. The study was prompted by the AOSTRA plans to expand the Underground Test Facility to a pilot operation. As part of this expansion, it is envisaged to dispose of residual waters by on-site deep well injection. Environment Canada and the Alberta Research Council initiated in 1990 a collaborative study on the effects of deep injection of residual water at the UTF site, with data support and cooperation from AOSTRA. The evaluation of the effects of deep injection of residual water is based on predictive modeling, which requires knowledge of the initial baseline hydrogeological conditions. Previous regional-scale studies of the hydrogeological regime in the sedimentary succession in northeast Alberta are too coarse for the resolution needed for predictive modeling at the UTF site. On the other hand, the data are very scarce and incomplete at the local scale. Thus, an intermediate-scale hydrogeological study is required for the identification and characterization of the hydrostratigraphic units at the UTF site, which form the content of this report.

The intermediate-scale hydrostratigraphy around the UTF site is less complex than at the regional scale because of the absence of Lower Elk Point Group halite beds and of extensive pre-Cretaceous erosion of Devonian strata. The sedimentary succession can be broadly divided into four main flow units (aquifers) separated by three barriers (aquitards or aquicludes). The flow of formation waters in the lowermost unit, the Winnipegosis-Basal aquifer, is regional in nature. The formation waters are very saline, with depth related trends. The halite and shale Prairie-Watt Mountain aquiclude separates this aquifer from the Beaverhill Lake aquifer above, which exhibits local flow regime characteristics. The formation water salinity is much fresher, and the flow directions are toward the northeast where the formation waters discharge at outcrop along the Athabasca River and its tributaries. The McMurray-Wabiskaw aquifer also has local flow-regime characteristics, being controlled by the topography and physiography of the area. The bitumen-saturated sands at the McMurray Formation seem to form a strong barrier, separating the flow systems in the Beaverhill Lake below and McMurray-Wabiskaw above, respectively. The shale Clearwater aquitard, overlying the McMurray-Wabiskaw aquifer, appears to be a strong barrier to flow. However, its integrity in places may be questionable because of recent and present-day erosion. The post-Clearwater aquifers of Grand Rapids and Pleistocene strata are of limited extent, with paleo-valleys cutting down in places into the Clearwater aquitard.