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TitlePaleovalleys revealed by bedrock topography and drift thickness mapping show potential for shallow gas, northwestern Alberta, Canada
AuthorPawlowicz, J G; Nicoll, T J; Fenton, M M; Rokosh, D; Ahmad, J; Schmitt, D R; Plouffe, A
SourceExploring energy systems: 2005 Canadian Association of Petroleum Geologists-American Association of Petroleum Geologists Joint Annual Convention: abstracts; 2005, 1 pages
Alt SeriesEarth Sciences Sector, Contribution Series 2004440
PublisherAmerican Association of Petroleum Geologists (Tulsa, OK, USA)
MeetingCanadian Society of Petroleum Geologists - American Association of Petroleum Geologists 2005 Joint Annual Convention; Calgary, Alberta; CA; June 19-22, 2005
Mediaon-line; digital
File formathtml
AreaNorthwestern Alberta
Subjectsfossil fuels; sedimentology; bedrock geology; glacial deposits; drift deposits; bedrock geology; fluvial deposits; fluvial systems; tills; glaciolacustrine deposits; reservoirs; hydrocarbon migration; permeability; hydrocarbons
ProgramNorthern Resources Development Program
LinksOnline - En ligne
Quaternary mapping studies being conducted by the Alberta Geological Survey and Geological Survey of Canada in Northwestern Alberta have identified deeply buried valleys eroded into the bedrock and infilled with as much as 350 m of drift. The drift primarily consists of unconsolidated glacial Quaternary sediments with lesser amounts of pre-glacial Quaternary or Late Tertiary sediments. As a result of the multiple glacial advances and retreats during the Quaternary, the bedrock is almost entirely covered by drift. Subsurface mapping of the drift has identified several topographic depressions in the bedrock surface that are interpreted to be deeply buried valleys of glacial or pre-glacial origin. Many contain fluvial sediments near their base overlain by tills and/or glaciolacustrine clay units separated by glaciofluvial sediment. Clay-rich tills and glaciolacustrine deposits act as impermeable beds or reservoir seals within the Quaternary package.
Fluvial and glaciofluvial sequences, at the base and within the drift, may form gas reservoirs and/or aquifers. In places where the paleovalleys have intersected the gas-bearing Cretaceous Bluesky Formation, it is speculated that the hydrocarbons have migrated from the bedrock through the permeable fluvial and glaciofluvial sediments and become trapped by the impermeable units. High resolution seismic data collected by the University of Alberta from a 10 km line over a paleovalley shows incision down through the Bluesky Formation to the Devonian Wabamun surface. Preliminary interpretation shows stacked channels within the drift and possible gas-bearing 'bright spots' which appear to correspond to Quaternary gas production from offset wells.