Duhamel: A seismic analysis of differential compaction in a Leduc reef

R. James Brown, N. L. Anderson, D. A. Cederwall, Zandong Sun, Peter Malcolm Manning, Qi Zhang

The Duhamel reef is an isolated Frasnian limestone bioherm of the Leduc Formation in south-central Alberta. Although Duhamel has a relatively small basal area (less than 12 km2), the reef rises some 275 m above the platform facies. The seismic data show what we interpret to be a raised peripheral reef rim, which appears to be elevated about 25 m relative to the interior of the reef. Raised rims are commonly considered to be diagenetic in origin, and attributed to differential compaction within reef complexes. Although late-stage accretionary growth about the periphery of the reef complex may have contributed to its development, we interpret the raised rim at Duhamel to be principally of secondary origin. This thesis is supported by the incorporated seismic and well-top data.

The seismic data also suggest that the facies within the reef rim have a lower seismic velocity than the facies within the structurally lower reef interior, consistent with the observation that raised rims are generally more porous than the encircled and structurally lower lagoon and, therefore, constitute a preferred well-completion site. Optimal hydrocarbon recovery could be realized if all producing wells were drilled into the raised reef rim. Our data for Duhamel show that even relatively small reefs can exhibit raised rims and that these rims may be seismically visible, especially if one can incorporate multicomponent and/or 3-D data. Such data should be acquired prior to drilling across similar reefs with a view to imaging and locating the complete raised rim, not simply its updip side, so that all parts of the rim can be targeted for the drill.