Abstract

The Swan Hills reef at Simonette is a complex, multi-cyclic body formed by a series of stacked reef growth stages which exhibit variable geometries. The entire buildup is broadly subdivided into seven stages. Stage I is a regional platform that is not considered part of the reef proper. The lower parts of the reef (Stages II and III) consist of semi-isolated shoals and carbonate islands separated by channels filled with high velocity argillaceous limestones. These shoals and channels were then partly eroded (?) and subsequently overstepped by a more widespread carbonate bank facies during stages IV and V. The reef edge of this widespread bank sequence exploits a combined Stage II and Stage III break in slope. The widespread bank in turn passes up to two backstepping, ramp-like sequences in Stages VI and VII. Reservoir is mostly present in dolomite. Dolomitizing fluids were hydrothermally sourced through vertical faults and fractures but then migrated laterally through the reef within high energy facies (grainier and faunal-rich facies with high original porosity). Consequently, dolomitization and reservoir are best developed in facies tracts close to the reef margin, becoming increasingly patchy and heterogeneous into the reef interior and off-reef.