Regional-scale hdyrogeology of the Upper Devonian-Lower Cretaceous sedimentary succession, south-central Alberta basin, Canada

摘要

The flow of formation waters in the Upper Devonian-Lower Cre- taceous sedimentary succession in the south-central part of the Alberta basin is controlled mainly by (1) outcrops of Devonian and Mississippian strata at high elevation in the south in Mon- tana, and at low elevation at the Peace River in the north; (2) sub crops of Devonian to Jurassic strata at the sub-Cretaceous unconformity; and (3) deposition of Cretaceous sediments on pre-Cretaceous relief exposed for a long period of time. Weath- ering of Upper Devonian strata during this long period of sub- aerial exposure and the concurrent paleokarsting of the Grosmont Formation led to high permeability in these aquifers. As a result, the Grosmont aquifer and the Upper Devonian aquifer system that sub crop at the sub-Cretaceous unconformity form a drainage path in a northward regional-scale flow system in the southern and central parts of the Alberta basin. This long-range flow sys- tern is fed by meteoric recharge in the south, by up dip flow of connate waters from deep Paleozoic aquifers that sub crop along " the western flank of the main system, and by downdip meteoric i recharge through Cretaceous strata along the eastern basin edge. lA plume of relatively high salinity is formed in the Lower Mann- ville aquifer in the area where highly saline Devonian waters dis- , charge at the sub-Cretaceous unconformity and mix with fresh 1 water of meteoric origin. IHydrocarbons generated in Upper Devonian to Lower Cretaceous strata of the deep foreland basin migrated northeast- r ward up dip, driven by uoyancy and supported by a concur- rent hydrodynamic drive. The great majority of the generated .I. hydrocarbons reached the sub-Cretaceous unconformity , where they were trapped in complex stratigraphic traps in the Lower Mannville Formation. Downward flow of meteoric water along the eastern flank of the basin hydrodynamically enhanced the trapping and led to hydrocarbo biodegradatio in place into heavy oils and oil sands in the Cold Lake and Athabasca areas.