Geological Setting for Shallow Gas in Quaternary Sediments of Northern Alberta

This 64-page presentation was given at the annual meeting of the Canadian Society of Petroleum Geologists, June 2003.

Abstract

Recent years have seen an increased level of exploration for shallow gas in Northern Alberta. One such area, the Sousa field near High Level has been producing gas from thick Quaternary sediments since 1998, but other areas with similar geology are present throughout Northern Alberta. Shallow gas has been discovered at a variety of locations and at depths of a little as 30 m.

The last major geological events to modify the present-day landscape were the multiple glacial advances and retreats during the Quaternary. These left a drift cover which in part masks both the board uplands and deep channels of the preglacial drainage system.

Major preglacial valleys are present throughout Northern Alberta with drift thickness accumulations of over 200 m. Many contain preglacial fluvial sediments near their base which are overlain by tills or glaciolacustrine clays separated by fluvial sediment. The fluvial sediments commonly are sands and gravel of either preglacial or glacial age. The tills are characteristically clay rich because the source material during glacial erosion and deposition was from the underlying Cretaceous-aged shale bedrock.

The drift, in general, consists of alternating fluvial sequences, which can form aquifers and/or gas reservoirs and till and glaciolacustrine layers which form aquitards and/or caprocks. These fluvial channel may be confined between till layers or have eroded through underlying till to intersect the underlying glaciofluvial or in some situation the underlying preglacial sediment.

The Alberta Geological Survey is conducting a multiyear program of mapping the bedrock topography and drift thickness of Northern Alberta at 1:250 000 scale, and characterizing the drift sediments to eventually provide a basis for developing a stratigraphic framework throughout the area. However data are already available for some on the areas in the central and northwestern part of the region.

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