LeSchack, Leonard A.1, Richard E. Wyman2, John R.
(1) Hectori Inc, Calgary, AB
(2) Dyloc Exploration Inc, Salt Lake City, UT
(3) Pinemont Technologies Inc, Littleton,
ABSTRACT: Surface Exploration Successful in Finding Alberta Leduc Pinnacle Reefs
Prolific pinnacle reefs that are typically associated with the larger reef trends have proven difficult to locate in Alberta. But when they are, they can be enormously profitable. In 1982, Gulf Canada Resources discovered a small pinnacle, called the Rumsey Reef, which produced over 3.7 million barrels of high gravity oil from one well. During the first three years it flowed 3-4000 B/D. Despite intensive drilling to the Leduc during the next two decades, results, with very few exceptions, were most disappointing. What is the explanation?
The present authors believe they have the answer: Probably most of the remaining Leduc pinnacle reefs in central Alberta, and we have measured many of them, are physically too small to be adequately resolved by reconnaissance seismic exploration, whether 2D or 3D. Our non-seismic measurements suggest pinnacle reefs, some similar to Rumsey in size, are pillars of coral growing between 550' to 700' high from the Cooking Lake carbonate platform. They appear to range from 70' to 225' in diameter. Structures of this physical size will likely result in seismic anomalies that would go unnoticed or deemed not of interest by seismic interpreters.
Using high resolution ground magnetic surveys and passive telluric technologies we have located and detailed the geometry of several reefs. We drilled for one reef, so defined, and it was discovered within 30’ of the depth predicted. Logs from the well, 14-29-59-19W4, aimed at this reef, display as much Leduc buildup as seen in the Rumsey Reef well logs. Our current work suggests that by using non-seismic geophysical measurements of anomalies, small reefs as well as large ones can be relatively inexpensive to locate and define.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.