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of Formation Waters, Aquifer Characteristics, and Their Relation to Hydrocarbon
Accumulations, Northern Alberta Basin1
Based on the wealth of data generated by
the oil industry, the regional-scale characteristics of rocks, the flow
of formation waters, and their relation to hydrocarbon accumulations were
analyzed for the northern Alberta basin. The flow of formation waters in
several aquifers and aquifer systems separated by intervening aquitards
is at steady state and is driven by the present-day topography both on
a regional and a local scale. The flow is generally from a recharge area
in the southwest at the fold belt and Bovie Lake fault, to discharge in
the northeast at the Great Slave Lake, the lowest point in the basin. The
flow in Devonian aquifers is in open systems from recharge to discharge
areas, whereas the flow in Carboniferous and Cretaceous aquifers is in
semi-open systems, discharging into adjacent aquitards. Very high porosity
and permeability in places in the Devonian Elk Point aquifer system are
due to reefs, fracturing, dolomitization, and karst processes. Very high
permeability probably leads to relatively high flow rates along the Presqu'ile
barrier reef, resulting in local advective effects on the terrestrial heat
transport to the surface. On a regional scale, all of the aquifers are
underpressurized due to upstream propagation through high-permeability
zones of low hydraulic heads at discharge elevations. The flow pattern
is corroborated by salinity distributions, with comparatively lower salinity
in each aquifer at recharge in the southwest and at discharge in the northeast
caused by mixing with fresher meteoric water, and higher salinity between
recharge and discharge areas. Salinity distributions show that the aquifers
are not completely flushed of the original formation waters. Dissolution
of salt and anhydrite from adjacent strata leads to high salinity in the
Elk Point aquifer system and Beaverhill Lake aquifer.
1997. The American Association of Petroleum Geologists. All rights reserved.
received January 15, 1996; revised manuscript received July 8, 1996; final
acceptance November 22, 1996.
Geological Survey, Edmonton, Alberta T5K 2G6, Canada.
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