Hydrocarbon generation and migration in the Western Canada sedimentary basin

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Abstract
A total of ten marine, petroleum source rocks ranging in age from Middle Devonian to Late Cretaceous exist within the Western Canada Basin. Principal hydrocarbon reserves occur in the Lower Cretaceous Mannville Group and subcropping Paleozoic carbonates, where 270 × 10 9 m 3 (1.7 trillion barrels) of heavy oil form one of the largest deposits of oil on Earth. Biomarker analyses of these heavy oils, many conventional oils and most source rocks in the basin have been combined with basic geology to establish the source and migration history of the Western Canada Basin. Several pre-Cretaceous source rocks (principally the Lower Jurassic Nordegg Formation, the Mississippian Exshaw/Bakken Formation, the Triassic Doig/Phosphate Formation and the Upper Devonian Duvernay Formation) have contributed to the Mannville accumulations. The Joli Fou shale, overlying the Mannville, is a regional seal for the Mannville and older section. Oils present in the overlying Viking, Cardium, and Belly River sands are all of a single family, sourced from the Colorado Shale section and are quite distinct from the oils in the Mannville and older section. Meteoric water incursion at the eastern limb of the basin permitted biodegradation, which converted the conventional Mannville crude oil to heavy oil. The Western Canada Basin also contains an estimated 5 × 10 12 m 3 (180 TCF) of gas. Gas sources are the marine, oil-prone source rocks where overmature, as well as Lower Cretaceous Mannville coals and coaly shales. Hydrogen sulphide is contributed from overmature Paleozoic evaporites/carbonates with an estimated 36% of the total in-place gas reserves being classified as sour.