Regional Geology and Hydrostratigraphy in Northeast Alberta

The Alberta Oil Sands Technology and Research Authority (AOSTRA) is currently planning to expand the Underground Test Facility (UTF) near Fort McMurray in northeast Alberta to a commercial size operation. As part of this expansion, it is envisaged to dispose of produced residual waters by on-site deep well injection. Selection of a disposal zone is currently under way. The upgrading of the UTF operations provides an opportunity for monitoring possible environmental effects related to the deep disposal of waste water resulting from the in situ extraction of bitumen from oil sands. With this in mind, and the additional objective of developing strategies for similar future activities, Environment Canada and the Alberta Research Council initiated a collaborative study of the effects of deep waste injection at the UTF site, with data support and cooperation from AOSTRA.

The evaluation of the effects of deep injection of waste water is based on predictive modelling, which requires knowledge of the initial baseline hydrogeological conditions. Because the data are very scarce and incomplete at the local scale, a regional-scale hydrogeological study is required for the identification and characterization of the hydrostratigraphic units at the UTF site. For this purpose, a regional-scale study area is defined in northeast Alberta between latitudes 55°N and 58°N, and longitudes 110°W to 114°W (Tp 70-103, R 1-26, W4 Mer). The first step in the hydrogeological characterization is the description of the geology and the delineation of the hydrostratigraphy, which form the content of this progress report.

The geology and hydrostratigraphy of the Phanerozoic sedimentary rocks in northeast Alberta are extremely complex due to various depositional, salt dissolution and erosional events. The shales interbedded with sandstones, red beds and evaporitic units of the Lower Elk Point Subgroup (Lower Devonian) overlying the impervious crystalline Precambrian basement from a dominantly aquiclude system at the base of the succession. The overlying carbonates of the Winnipegosis aquifer are separated from the mainly carbonate Beaverhill Lake aquifer system by the halite and shale of the Prairie-Watt Mountain aquiclude system. The argillaceous Ireton aquitard separates the Beaverhill Lake and Grosmont-Wabamun aquifer systems. All the Devonian strata have been eroded and subcrop at the sub-Cretaceous unconformity. They are overlain by the succession of the McMurray, Clearwater and Grand Rapids formations of the Lower Cretaceous Mannville Group. These are defined as weak aquifer-aquitards because of a complex combination of interbedded sands, shales and oil sands. The Colorado aquitard system (mainly shales with a few sandy units) lies at the top of the hydrostratigraphic succession.

The hydrogeological characterization (porosity and permeability, formation pressure, and chemistry of formation waters) of the hydrostratigraphic units identified in this progress report will form the subject of the next research stage.