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Blind thrusts and fault-related folds in the Upper Cretaceous Alberta Group, deep basin, west-central Alberta: implications for fractured reservoirs

Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, QC H3A 2A7

Kurt J. Marfurt

Allied Geophysics Laboratories, Geosciences Department, University of Houston, Houston, TX 77204-5007

Bogdan L. Varban

Department of Earth Sciences, University of Western Ontario, London, ON N6A 5B7

A. Guy Plint

Department of Earth Sciences, University of Western Ontario, London, ON N6A 5B7

3-D seismic and log-based mapping of Upper Cretaceous units in the Deep Basin has revealed the presence of fault-related folds in the Cardium Formation and overlying units. The folds formed above low-angle thrust faults that cut clay-rich shales in the lower part of the Kaskapau Formation. Seismic data indicate a fold wavelength of approximately 5 to 8 km at the Cardium level, with fold axes trending NW-SE. Log-based stratigraphic analyses identified fault repeats of Kaskapau allomembers, whereas the 3-D seismic data show details of upward-branching fault splays and related folds. The faults also splay laterally, and transfer strain by overlapping. Post-stack processing of the original 3-D volume, including noise reduction, coherency processing, and volumetric dip analyses significantly improved our ability to image and map these structures.

The Cardium Formation produces oil in the study area from fields with orientations that are approximately parallel to the fold axes. These production trends are thought to be related primarily to depositional trends that predate the structural deformation. Nevertheless, the structures we illustrate are fractured, and so they are good analogues for potential drilling targets in similarly-deformed tight-gas reservoirs. Previously published core and borehole breakout studies support these interpretations.