Abstract

In the last decade or so, studies utilizing information from the more than 200 000 wells drilled in the Alberta basin to date have provided a good understanding at the regional scale of the patterns of formation water flow. The mechanisms driving the flow are also generally understood. In the Rocky Mountains and the thrust and fold belt, formation water flow is driven by topography in local systems. Two basin-scale flow systems in the undeformed part of the basin are also driven by topography. The first one, located north of the Peace River Arch, is recharged at the fold belt and Bovie Lake fault and discharges at Great Slave Lake. The second one, located in the southern and central part of the basin, is driven in a northward direction from high elevation outcrops of Devonian and Carboniferous strata in Montana to discharge along the Peace River where the Grosmont Formation crops out. Other intermediate- and local-scale flow systems driven by topography are present in the basin, mainly in the northeast. In the southwestern part of the basin, flow in Upper Cretaceous aquifers is driven inward downdip, toward the thrust and fold belt, by erosional rebound in thick intervening shaly aquitards. The flow in deep Paleozoic aquifers in the southwestern part of the basin is driven, probably by past tectonic compression, northeastward, updip toward the main northward basin-scale flow system. The increase of formation water salinity with depth, mainly in deep Paleozoic aquifers, retards the flow of formation water driven by hydraulic-head differences. High permeability Devonian reefs and carbonate platforms play the role of vertical pipes, lateral conduits and drains, allowing for cross-formational and focused flow. Although the basin is generally underpressured, zones of overpressures are present in tight strata in the deep part of the basin, most probably as a result of recent or current hydrocarbon generation. The complex pattern of flow of formation waters has influenced hydrocarbon migration and accumulation, played a role in the genesis of mineral deposits and in places still affects the geothermal regime in the basin. Regional- and basin-scale flow systems can serve for the hydrodynamic entrapment of liquid wastes and CO 2 injected into deep aquifers. Although a good understanding of the flow pattern in the basin has been achieved to date, there are a few issues that remain to be addressed. Such issues are the degree, if any, of interaction between flow systems in the deformed and undeformed parts of the basin, and between basement and the sedimentary succession, the effect of the last orogenic pulse, and the true magnitude and direction of formation water flow in the various systems.

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