Mineralogical composition, texture and diagenesis of the Upper Cretaceous (Campanian) basal Belly River sandstone reservoir in the Pembina-Keystone ‘B’ Pool were studied in core from nine wells. Study techniques included stereoscopic examination, thin-section petrography, scanning electron microscopy and X-ray diffraction analysis.

The basal Belly River sandstone ranges from 17 to 21 m thick and consists of fine- to medium-grained well- to very well sorted lithic arenite. It gradationally overlies the marine Lea Park Shale as a progradational complex of nearshore and shoreline sands, including deltaic channel sands with interbedded overbank deposits.

Diagenesis has involved mechanical compaction, cementation, replacement, recrystallization and simple solution. Calcite, silica and authigenic clay (especially kaolinite) cements are widespread and the main porosity reducing agents. Calcite occurs as a pore-filling mosaic whereas silica occurs as quartz and “chert” overgrowths. Authigenic clays (kaolinite, mixed-layer montmorillonite/illite?, and chlorite) occur as pore linings and pore fillings characterized by small crystal size and submicroscopic porosity. Replacement of detrital feldspar and rock fragments by calcite and phyllosilicates is common.

Porosity and permeability have been significantly modified by diagenesis, resulting in porosities of 5 to 23% as measured by Core Laboratory analysis, and from less than 1 to 13% as measured by thin-section point counting. The permeability values range from less than 1 to 700 md. The variation in the porosity and permeability is due mainly to cementation and secondary solution.

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