ABSTRACT

The hydrogeological study of formation waters in the northeastern part of the Alberta basin (defined as the area from 55 to 58°N and from 110 to 114°W) is based on information from 12,475 wells, 3187 formation-water analyses, 2531 drill-stem tests, and 452,030 core-plug analyses. Because the study area, covering approximately 76,000 km2, is located at the feather edge of the basin, local topography and physiographic features, particularly the Athabasca River system, exert a strong influence on the flow of formation waters in most of the aquifers. Generally, temperature seems to be the main controlling factor on salinity distributions. The salinity of formation waters increases in the vicinity of evaporitic beds, and decreases close to the surface because of mixing with fresh meteoric water introduced through local flow systems.

The Lower and Middle Devonian pre-Prairie aquifer systems, beneath the regionally extensive Prairie aquiclude, are characterized by regional topographically-driven flow updip to the northeast. This updip flow is opposed by buoyancy forces caused by salinity increase with temperature downdip to the southwest. The post-Prairie Devonian aquifers are characterized by transitional flow regimes. Because of erosion at the sub-Cretaceous unconformity and outcrop at the Athabasca River, local physiographic influences are superimposed on basin-scale regional flow in these aquifers. Hydraulic communication between the Beaverhill Lake-Cooking Lake and Grosmont aquifers is inferred in places caused by Cooking Lake reefs penetrating the intervening shales of the Lower Ireton aquitard. Finally, the Cretaceous aquifers all can be described as having local flow regime characteristics with no buoyancy effects as a result of recharge in topographically high areas and discharge in low regions along the valleys of the Athabasca River system.

The flow of formation waters in northeastern Alberta played an important role in the formation of the huge Athabasca oil sands deposits. Hydrocarbons that migrated into the area from the west were trapped into local reservoirs, and biodegraded and washed by fresh meteoric water introduced by local flow systems. Environmentally, the subsurface hydrogeology in the area imposes specific constraints on waste disposal in deep formations mostly because of the absence of a thick, continuous regional aquitard and because most aquifers subcrop at shallow depth or crop out and discharge along the valleys of the Athabasca River system and at the basin edge.

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