New Perspectives on Hydrocarbon Potential of Bakken and Torquay Formations, Southeastern Saskatchewan

L. K. Kreis¹, A. L. Costa¹, and K. G. Osadetz^2
1 Saskatchewan Industry and Resources, Regina, SK
² Geological Survey of Canada, Calgary, AB

Late Devonian to Early Misssissippian Bakken shales in the Williston Basin are believed to have generated and expelled hundreds of billions of barrels of oil, yet only a few tens of millions of barrels have been produced. Recently, horizontal drilling and large sand fracture completions have established significant Bakken production in Richland County, Montana. Careful examination of cores, geophysical logs and production data indicates strong potential for similar horizontal completions, by-passed pay and undiscovered oil in siltstones and sandstones of the middle member of the Bakken in southeastern Saskatchewan. In addition, a large area of anomalously high resistivity response within Bakken shale intervals has been mapped. In this area, Bakken shales appear to have retained a proportion of the generated oil within the formation, which may represent an enormous exploration target. Much of the oil reservoired within the Bakken shale likely resides in a network of enhanced porosity and permeability related to microfractures. Fracturing is interpreted to be related to hydrocarbon generation, where the combination of the excess pressure (hydrostatic stress) and tectonic stress, particularly that associate with, pre-existing structure, tectonic stress, motions on basement faults, salt dissolution and differential compaction during Laramide time may have resulted in a hydraulic fracturing of the Bakken Formation shales, which provides a mechanism for porosity and permeability improvement.

In recent years, dolostones and dolomitic siltstones of the Upper Devonian Torquay Formation, underlying the Bakken Formation, have also proven to be productive for the first time in Saskatchewan in an area along the Saskatchewan-Manitoba border.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005