ABSTRACT

The Leduc Rimbey-Meadowbrook reefs have produced prolific amounts of oil and gas for more than 40 years, yet their diagenesis is poorly known. We have initiated a study of their diagenesis and reservoir characteristics in order to determine whether a) they have served as a preferential conduit for fluid flow, and b) there are hitherto unrecognized diagenetic traps associated with the reef trend.

Petrographic and geochemical characteristics of Leduc dolomites suggest that replacement dolomitization was probably related to a major preferential conduit system in the Cooking Lake platform. Dolomitization being related to this conduit system explains several features of replacement matrix dolomites in buildups along the Rimbey-Meadowbrook trend: the similar selective replacement of limestone components, the relative homogeneous petrography and cathodoluminescence, their narrow range of carbon and oxygen isotopes (+2.2 to +3.5°/¹³C PDB, -6.7 to -5.0°/¹⁸O PDB), and low Sr (<150 ppm) and Mn (<250 ppm) concentrations. The presence of fabric-destructive dolomitization in the interior of the buildups and in the underlying Cooking Lake platform suggests that these were the zones where fluid flow was most active.

Similar features occur in matrix dolomites in Devonian buildups in the Rocky Mountains. Ongoing analyses of Leduc and Cooking Lake dolomites along the Rimbey-Meadowbrook trend, in conjunction with the study of Devonian dolomites elsewhere in the basin, will help to better determine their origin. This has implications for petroleum exploration and development.

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