Rejuvenation of a Mature Oil Field: The Devonian Leduc Formation at Innisfail Field, South-Central Alberta, Canada

Stacy C. Atchley¹, Lawrence W. West², and Jeff R. Sluggett^2
1 Baylor University, Waco, TX
² Chariot Energy, Inc, Calgary, AB

Oil has been continuously produced from the Devonian Leduc Formation at Innisfail Field since its discovery in 1957. To date, cumulative production is 98% of recoverable oil in-place (~ 85 mmbbl), and indicates that the Leduc is in the twilight of production. An integrated sequence stratigraphic framework generated during the summer of 2003; however, suggests that the productive life may be extended through the development of two previously undetected categories of bypassed oil entrapment: (1) “attic” oil accumulations associated with small, isolated bank-top buildups, and (2) backstep-edge accumulations located in positions structurally low to currently producing wells. In both cases, oil accumulations are related to a Leduc depositional history that was characterized by long-term carbonate sediment accumulation exceeded by the rate of sea level rise. Positive relief at the time of deposition, and subsequently, present-day stratigraphic traps were produced during the final phase of stratal retrogradation that immediately preceded “drowning” of the Innisfail carbonate bank. High quality 3D seismic data is essential in the exploration for both attic and backstep-edge oil accumulations at Innisfail. Integration of 3D seismic, well log and core data indicates that although depositional relief on both types of features may be low, they are nonetheless seismically resolvable. Attic features range from 200-300 m in diameter, and provide 2-7 m of closure above spill-point. Backstep-edge oil accumulations occur within the structurally highest portions of the Leduc G cycle downlap limit. Depositional relief, and associated trap closure on the Leduc G is less than 10 m. Targeted drilling during 2004 has resulted in a 50% increase in oil production.

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