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Reserves growth in a mature oil field: The Devonian Leduc Formation at Innisfail field, south-central Alberta, Canada

¹ Department of Geology, Baylor University, One Bear Place 97354, Waco, Texas 76798-7354; stacy_atchley{at}baylor.edu
² Auriga Energy Inc., Suite 680, 140-4th Avenue S.W., Calgary, Alberta, Canada, T2P 3N3
³ J. R. Sluggett Geophysical Consulting Ltd., 144 Edelweiss Drive, N.W., Calgary, Alberta, Canada, T3A 3R1

Stacy Atchley received his B.S. and M.S. degrees from Baylor University in 1984 and 1986 and his Ph.D. from the University of Nebraska in 1990. After working for Exxon Company, U.S.A., and Exxon Production Research from 1986 to 1995, Stacy rejoined Baylor, where he currently directs the Applied Petroleum Studies Program and is a researcher in the Ancient Environment Reconstructions Research Group.

Lawrence West received his B.Sc. (hons.) degree in geology from McMaster University in 1979 and his M.B.A. from the University of Calgary in 1989. His career began with Esso Resources Canada, Ltd., and Alberta Energy Company. He is currently the vice president of Geoscience with Auriga Energy Inc. Revitalization of mature fields is an area of interest.

Jeff Sluggett received his B.A.Sc. degree in geological engineering from the University of British Columbia in 1973. Jeff worked as an explorationist for Amoco Canada from 1973 to 1980 and was chief geophysicist and international corporate exploration advisor for Ranger Oil from 1980 to 2000. Jeff currently works for several companies in Calgary as a geophysical consultant specializing in three-dimensional seismic interpretation.

ABSTRACT

Oil has been continuously produced from the Devonian Leduc Formation at Innisfail field since its discovery in 1957. To date, cumulative production at Innisfail is 98.9% of recoverable oil in place (84.3 MMBO) and indicates that the Leduc is near the end of its productive life. A sequence-stratigraphic interpretation produced from core, well logs, and three-dimensional (3-D) reflection seismic data, however, suggests that production may be extended through the development of two previously undetected scenarios of bypassed oil entrapment: (1) attic oil accumulations associated with small buildups atop the isolated Innisfail platform 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 rates of long-term carbonate sediment accumulation exceeded by the rate of sea level rise. Positive bathymetric relief created at the time of deposition and, subsequently, present-day stratigraphic traps were produced during the final phase of stratal retrogradation that immediately preceded the drowning of the isolated Innisfail platform.

High-quality 3-D seismic data are essential in the exploration for both attic and backstep-edge oil accumulations at Innisfail. Integration of 3-D seismic data, well-log, and core data indicates that although depositional relief on both types of features may be low, they are nonetheless seismically resolvable. The small platform-top buildups are up to 0.16 km² (40 ac) in diameter and have up to 10 m (33 ft) of independent closure above spill point. Backstep-edge oil accumulations occur within the structurally highest parts of the Leduc high-frequency sequence G downlap limit. Depositional relief along the downlap limit and associated trap closure ranges from approximately 5 to 15 m (16 to 49 ft). During 2003 and 2004, two platform-top buildups were directionally drilled, and one existing well located near a backstep-edge position and suspended since 1988 was reactivated. All three wells are successful and, to date, have cumulative production of 71 thousand bbl of oil. A total of 17 platform-top buildups and backstep-edge development drilling prospects exist across Innisfail and have expected-case recoverable reserves of approximately 960 thousand bbl of oil. These reserve additions suggest the potential for 1.14% field growth at Innisfail and are representative of the potential value that may yet exist within all mature Leduc fields in western Canada.

This article has been cited by other articles:

				S. C. Atchley, D. M. Cleveland, and L. W. West A case for renewed development of a mature gas field: the Devonian Swan Hills Formation at Kaybob South field, Alberta, Canada Bulletin of Canadian Petroleum Geology, June 1, 2008; 56(2): 165 - 190. [Abstract] [Full Text] [PDF]