Bulletin 061

Bulletin 061

BUL 061

Regional-Scale Subsurface Hydrogeology in Northeast Alberta

The hydrogeological regime of formation waters in the Phanerozoic sedimentary succession was determined for a region defined as Tp 70-103 W4 Mer (55-58 degrees;N latitude and 110-114 degrees;W longitude) in northeast Alberta, covering most of the Athabasca Oil Sand Deposit. The study was based on information from 12,479 wells, 3187 analyses of formation water, 2531 drillstem tests and 452,030 core analyses. Data management and processing were carried out using the INGRES Data Base Management System and specially designed software developed at the Alberta Geological Survey.

The regional geology was synthesized in terms of definable stratigraphic successions, and 26 individual units were characterized by structure top and isopach maps. The hydrostratigraphy was developed through several iterations starting from the stratigraphy and lithology of the strata. Complex groups of aquifers and/or aquitards exhibiting generally common overall characteristics were grouped into hydrostratigraphic systems. Thirteen hydrostratigraphic units were identified in the Phanerozoic succession. The hydrogeological regime in aquifers was described using isopach, salinity distributions and freshwater hydraulic-head distributions. Cross-formational flow was evaluated using plots of pressure variation with depth in selected wells.

Because the study area is situated at the feather edge of the Alberta Basin, topography and physiographic features exert a strong influence on the flow regime within most aquifers. In the most general sense, fluid flow is to the northeast toward the edge of the basin. Areas of high topography, such as the Birch and Pelican mountains, act as local recharge areas, introducing fresh meteoric water to aquifers unprotected by significant confining strata. The valleys of the Athabasca River system represent discharge areas for aquifers at outcrop or subcropping near them.

The salinity of formation waters generally increases with depth. This is the result of a combination of factors like temperature, hence solubility increase with depth, dissolution of deep Devonian evaporitic beds, and dilution near the surface by meteoric water introduced by local flow systems. In terms of flow regime and overall characteristics, the hydrostratigraphic units can be grouped into pre-Prairie Formation aquifers, Beaverhill Lake-Cooking Lake aquifer system, Grosmont-to-Wabamun aquifers, and Cretaceous aquifers. The aquifers below the Prairie evaporite exhibit regional flow-regime characteristics. Overall high formation water salinity is associated with the proximity of Elk Point Group evaporites. The Beaverhill Lake-Cooking Lake aquifer system has hydrogeological characteristics consistent with an intermediate-to-local flow regime. Within subcrop and outcrop areas, local physiographic influences are superimposed over a regional northeastward flow trend. The Grosmont aquifer and Winterburn-Wabamun aquifer system may act locally as a 'drain' for aquifers in hydraulic continuity above and below. The flow of formation waters is generally to the northwest, towards discharge at outcrop along the Peace River. The Cretaceous aquifers are characterized by low salinity and local flow regime.The synthesis of this vast amount of information on the hydrogeological regime of formation waters in northeast Alberta was carried out under a jointly funded research project by the Alberta Research Council and Environment Canada.

Bachu, S., Underschultz, J.R., Hitchon, B. and Cotterill, D.K. (1993): Regional-scale subsurface hydrogeology in northeast Alberta; Alberta Research Council, ARC/AGS Bulletin 61, 49 p.