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AAPG Bulletin
Abstract
AAPG Bulletin, V.
Regional-scale hydrogeology of the Upper Devonian-Lower Cretaceous sedimentary succession, south-central Alberta basin, Canada
S. J. Anfort,1 Stefan Bachu,2 L. R. Bentley3
1University of Calgary; current address: Marathon Oil Company, 5555 San Felipe, Houston, Texas, 77056
2Alberta Geological Survey, 4th Floor, Twin Atria, 4999-98 Avenue, Edmonton, Alberta, T6B 2X3, Canada; email: [email protected]
3Department of Geology and Geophysics, University of Calgary, Calgary, Alberta, Canada, T2P 1G2
AUTHORS
Stephen Anfort obtained his B.Sc.E. degree in geological engineering from Queen's University in 1992 and an M.Sc. degree in geology from the University of Calgary in 1998. He was first introduced to petroleum hydrogeology through working for two consulting firms in Calgary between 1992 and 1996. Since 1998 he has worked as a geologist in the Gulf of Mexico Exploration Team with Marathon Oil Company in Houston.
Stefan Bachu has engineering and M.Sc. degrees and a Ph.D. in hydraulics, hydrogeology, and transport processes. After postdoctoral research at Cornell University, he joined in 1983 the Alberta Geological Survey in Edmonton, Canada, where he currently is geoscience advisor and leader of the Energy Section. His areas of interest and specialization include hydrogeology and geothermics of sedimentary basins, reservoir and aquifer analysis and characterization, and, more recently, sequestration of CO2 in geological media in response to climate change. He applies his interests to the platform-margin and foreland Alberta basin.
Laurence R. Bentley is an associate professor in the Department of Geology and Geophysics, University of Calgary. He received his B.A. degree in physics in 1971 from Hamilton College and his M.Sc. degree in geology and geophysics in 1974 from the University of Hawaii. He worked for ten years with Western Geophysical Company as a geophysicist and research geophysicist. In 1990 he received his Ph.D. in civil engineering from Princeton University. He joined the University of Calgary in 1991 and specializes in subsurface flow and transport and geophysical applications to fluid flow problems.
ACKNOWLEDGMENTS
Stephen Anfort would like to acknowledge funding support from the Alberta Geological Survey, from a NSERC grant awarded to Laurence R. Bentley, and from the Department of Geology and Geophysics, University of Calgary. We wish to express our thanks to M. Grobe from the Alberta Geological Survey for help in identifying wells where cross-formational flow is possible, to W. Hoyne from the University of Calgary who helped with the graphic material, and to K. Parks from Petro-Canada Ltd. and an anonymous reviewer, whose useful comments helped improve the quality of the manuscript.
ABSTRACT
The flow of formation waters in the Upper Devonian-Lower Cretaceous 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 Montana, and at low elevation at the Peace River in the north; (2) subcrops 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. Weathering of Upper Devonian strata during this long period of subaerial 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 subcrop 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 system is fed by meteoric recharge in the south, by updip flow of connate waters from deep Paleozoic aquifers that subcrop along the western flank of the main system, and by downdip meteoric recharge through Cretaceous strata along the eastern basin edge. A plume of relatively high salinity is formed in the Lower Mannville aquifer in the area where highly saline Devonian waters discharge at the sub-Cretaceous unconformity and mix with fresh water of meteoric origin.
Hydrocarbons generated in Upper Devonian to Lower Cretaceous strata of the deep foreland basin migrated northeastward updip, driven by buoyancy and supported by a concurrent hydrodynamic drive. The great majority of the generated 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 (Begin page 638) the eastern flank of the basin hydrodynamically enhanced the trapping and led to hydrocarbon biodegradation in place into heavy oils and oil sands in the Cold Lake and Athabasca areas.
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