Large-scale underpressuring in the Mississippian-Cretaceous succession, Southwestern Alberta Basin
- Alberta Geological Survey, Edmonton (Canada)
The hydrodynamic regime of formation waters in the post-Devonian sedimentary succession was studied for an area of about 120,000 km{sup 2} in southwestern Alberta using approximately 15,000 drill-stem tests and 13,000 formation-water analyses. The salinity of formation waters generally increases both northward and with depth from 5000 mg/L to more than 100,000 mg/L. Based on flow characteristics and driving mechanisms, the sedimentary succession can be divided into two megahydro-stratigraphic groups overlain by an unconfined aquifer at the top. The Mississippian-to-Mannville (Cretaceous) hydrostratigraphic group is basically an open hydrodynamic system dominated by aquifers. The flow of formation waters is driven by basin-scale topography, and part of a basin-scale flow system with recharge at high elevations in the south and southwest and discharge at low elevations in the north-northeast. The Cretaceous Colorado-to-Edmonton hydrostratigraphic group is largely a closed hydrodynamic system dominated by aquitards. The flow in aquifers is driven west-ward downdip, toward the thrust and fold belt, by large-scale underpressuring caused by erosional rebound in thick shales. In places, pressures reach lower values than those corresponding to the lowest basin elevation located far to the north. This flow system is in a transient state of mechanical and hydrodynamic adjustment to the present topography. The different flow pattern in the two megahydrostratigraphic successions has consequences for hydrocarbon exploration in terms of secondary migration paths and possible hydrodynamic entrapment of hydrocarbons.
- OSTI ID:
- 90873
- Journal Information:
- AAPG Bulletin, Vol. 79, Issue 7; Other Information: PBD: Jul 1995
- Country of Publication:
- United States
- Language:
- English
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