Geology of Hydrocarbon Occurrence in Woodbend Reefs (Devonian) of Western Canada: ABSTRACT

Abstract

The Upper Devonian Woodbend reefs of central Alberta contain important hydrocarbon reserves. The discovery of 200 million bbl of oil in the Leduc reef in 1947 launched the modern petroleum industry in Canada. The generation and capture of crude oil and natural gas in major pools require the associated development, within a depositional basin, of adequate volumes of petroleum source rock, reservoir rock, and strata configurations capable of trapping the hydrocarbons entrained in the fluid systems operative within the basin. The occurrence of the 3 requirements in relatively close proximity within the time-space realm provides a maximum opportunity for major hydrocarbon accumulations to form. The Upper Devonian Woodbend Group of western Canada provided such an opportunity in central Alberta. It was deposited during a vast southerly transgression of the continent. Many depositional environments were present throughout the great length of the epicontinental basin. Clastic sedimentation dominated the northern open marine part of the basin, and shelf carbonates and evaporites were deposited in the shallow seas of the southern part. Biotic and depositional conditions, unique to the basin as a whole, developed along the margins of the carbonate seas. Biohermal reefs formed amid organically rich shale banks and both were enveloped within a short period of time End_Page 843------------------------------ by organically lean, eventually impervious, shale. Source rock, reservoirs, and traps for petroleum were closely associated. Subsequent sedimentary loading brought about maturation, fluid migration, and trapping. The pools were formed before Cretaceous time. End_of_Article - Last_Page 844------------