Great volumes of oil and gas have been generated, migrated and trapped in the clastic sediments of the Lower Cretaceous Mannville Group (Kootenai Formation equivalent) of the Western Canada basin. Aptian to middle Albian depositional environments have been summarized in a series of paleogeographic maps which show the many potential reservoir sands in their geological setting. The maps illustrate the important phases, or “events,” of a general sea-level rise in the basin.
Lower Mannville continental sediments of Aptian age deposited on a mature, erosional surface of Early Cretaceous to Paleozoic beds were inundated by a southward transgression of the Boreal Sea. Major northwest-trending fluvial systems were encroached and ultimately an interior seaway was extended into Montana. In Albian time, a terrigenous influx of Cordilleran origin prograded upper Mannville coastal and continental deposits more than 300 mi (480 km) from southern to northern Alberta. A multitude of shoreline sand trends which span Alberta in an east-west direction were deposited. The Mannville Group was capped by marine shales of the middle Albian Boreal and Gulfian (Skull Creek) seas which joined and inundated the western interior basin of North America.
Mannville sand trends contain an array of hydrocarbon traps including western gas-saturated “Deep basin” reservoirs, conventional stratigraphic oil and gas traps, and structural-stratigraphic traps in the heavy oil region of eastern Alberta and western Saskatchewan.
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Elmworth: Case Study of a Deep Basin Gas Field
This publication documents the geology and techniques used to explore Elmworth, the largest gas accumulation in Canada. Elmworth is peculiar in that gas lies downdip from water although no impermeable barrier lies between.