Abstract

Geochemical controls on the generation and accumulation of oil and gas have been reviewed in several Canadian sedimentary basins. Application of the thermal model of oil and gas generation allows zones of oil generation to be delineated on a regional scale in areas such as the Sverdrup Basin, Beaufort-Mackenzie Basin, Alberta Basin and East Coast Offshore. Strata containing marine organic matter within these zones can be identified as potential petroleum source rocks. In some cases, sediments containing dominantly terrestrially derived organic matter have some oil source potential.

Local variations in maturation due to salt domes and igneous intrusions can be demonstrated in the Scotian Shelf and the Sverdrup Basin, respectively. However, there are hydrocarbon occurrences that do not fit a simple model of hydrocarbon generation. In the Sverdrup and Alberta Basins, the occurrences of substantial reserves of dry gas in the marginally mature or undermature zones suggests that over-maturity is not a prerequisite for the formation of such gas. In the same way, modifications to the hydrocarbon generation model are required in order to explain the occurrence of gas condensate and some oil in marginally mature Upper Cretaceous-Tertiary sediments of the Beaufort-Mackenzie Basin and the Cretaceous sediments of the Scotian Shelf. In the eastern part of Alberta, extensively biodegraded heavy oil shows evidence of generation at relatively low levels of thermal maturation.

It is evident that the nature of the source organic matter for hydrocarbons is quite variable both in character and in level of maturity at which hydrocarbons are generated. Understanding these variations, therefore, is critical in determining the time of hydrocarbon generation and entrapment.