Sour-Gas Potential in Devonian of Western Alberta, Canada

James A. Podruski

The Geological Survey of Canada is presently conducting an assessment of the undiscovered gas resources of the Western Canada sedimentary basin using the exploration play analysis technique. The first system being examined is the Devonian, which has been divided into four exploration districts based on differences in depositional and tectonic histories, hydrocarbon compositions, and exploration practices. The western Alberta sour gas district contains most of the Devonian gas reserves (10 trillion ft³ of marketable gas) and potential in 12 exploration plays. Production in the Upper Devonian Swan Hills, Leduc, and Nisku formations is from the updip (northeast), basinward termination of carbonate shelves or large reef complexes and their associated patch and pinn cle reefs. Mapping the reef or shelf carbonate transition to basinal shale and carbonate delineates the play areas in these formations. Production in the Upper Devonian Wabamun Formation is from stratigraphic traps at shelf carbonate/shelf evaporite transitions and in structural-stratigraphic traps in dolomitized shelf carbonate. Pools in these plays typically contain from 50 to 500 billion ft³ of marketable gas, have 10-30% H₂S, and occur at depths from 8,000 to 15,000 ft. Potential in most plays is large, considering that between 90 and 99% of the play areas are unexplored. Present exploration is still concentrating on the conventional shelf margin or reef traps, such as in the area of the recent Caroline discovery. Subtle intrashelf traps are only beginning to be explored and could constitute a major resource target of the future, provided that economic conditions and improvements in seismic technology and geologic understanding will sustain the exploration effort in this district.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.