Abstract

The Mannville Group in northeastern Alberta was deposited during the Early Cretaceous in a south- to north-trending valley system on the pre-Cretaceous unconformity surface. The Mannville Group overlies eroded Devonian carbonates and is overlain by the shale-dominated Colorado Group equivalent. Mannville Group strata are composed of fluvio-estuarine and marine siliciclastic sediments. Hydrostratigraphically, the Mannville succession can be subdivided into four aquifers separated by three intervening aquitards. The four aquifers are, from the base up, the basal McMurray, upper McMurray Wabiskaw, Clearwater and Grand Rapids sandstones. The intervening aquitards are the bitumen-saturated middle McMurray and the Wabiskaw and Clearwater shales. The flow of Mannville Formation water is driven by local topography from recharge at highlands in the southeast and at the Stony Mountain upland in the centre of the study area, to discharge along the valleys of the Athabasca, Clearwater and Christina rivers. In the southwest, the flow in the basal McMurray and upper McMurray–Wabiskaw aquifers is drawn toward the basin-scale drain formed by the underlying Devonian Grosmont aquifer. Vertical flow in the study area is downward, from the ground surface toward the pre-Cretaceous unconformity. Application of the Steam Assisted Gravity Drainage (SAGD) process for in situ bitumen extraction from the McMurray Formation raises several hydrogeological issues: sustaining the large volumes of water needed for steam production; safely disposing of any produced residual water; protecting energy and groundwater resources; and avoiding large-scale cross-formational flow.

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