The Alberta basin covers part of three provinces in Western Canada, namely, British Columbia, Alberta, and Saskatchewan. It is 340,000 square miles in area and contains 485,000 cubic miles of sediments. The first geological work was carried out in 1857 by Sir James Hector and the first commencai production of gas began in Medicine Hat in 1890. As of December 1954, 8,760 crew months of geophysical work have been carried out; 3,330 exploratory wells have been drilled with the discovery of 104 oil fields and 83 gas fields. Oil reserves are estimated at approximately 2 billion barrels.
This paper does not cover in detail the geology and information on the basin but stresses that the keynote of the oil accumulations to date is that the major part of the oil (95 per cent) has been found in stratigraphic traps of two types—1. Devonian reefs, and 2. Cretaceous sand pinchouts in a homoclinal area with dips of a degree or less. From a depositional point of view both types are developed in shallow shelf areas. The variations in stratigraphy were probably caused by shifts in basin shape and microtectonics in the immediate vicinity but these latter cannot be mapped structurally today.
The occurrence of the Devonian reef fields is discussed, showing the relationship of these fields to the changes in shale-carbonate ratios. The Viking sandstone is used as the example of Cretaceous sand pinchouts and the oil and gas fields are shown with relationship to the Viking member itself and to the regional changes in sand thickness. As shown by isogravity maps a similar quality oil is found in both the Devonion reef and Cretaceous sands and very little change occurs over a broad areal extent regardless of present depth of burial.
The similar types of crude are indicative of similar environments and tectonic history. Long-range vertical or lateral migration from a central source is probably not the answer. The ideal relationship of source and reservoir rock appears to be the association of relatively small anaerobic lagoons or embayments set up in a shallow sea by restriction of currents due to reef growth or sand bar developments.
Figures & Tables
The history of oil exploration in a large basin is very much like the history of research in most fields of investigation. In the history of research into the subject of oil occurrence, however, the rate of increase of knowledge has fluctuated greatly. Sourced from the 1955 AAPG Annual Meeting, this publication contains many of the papers presented at that meeting, which discuss the habitat of most of the oil found in the world prior to 1955.