Integrated petrophysical evaluation of the Lower Middle Bakken Member in the Viewfield Pool, southeastern Saskatchewan, Canada

Abstract

The Viewfield Pool of the Lower Middle Bakken Member, the largest light oil pool in Saskatchewan, Canada has been described as an unconventional resource play. Reservoir evaluation in this pool has been challenging because of low permeability, complex lithology and reservoir heterogeneity. To address the difficulties, this study employed an integrated approach to derive reservoir parameters and provided a detailed petrophysical characterization of the Viewfield Middle Bakken play, which led to a division of Unit A, the Lower Middle Bakken Member into two subunits: A1 for the lower interval and A2 for the upper interval. Petrophysical models were developed based on thorough analyses of core measurements, conventional well logs and available advanced nuclear magnetic resonance (NMR) well log data. The proposed models were applied to determine reservoir properties including shale content, porosity, permeability and water saturation for the two subunits in 163 vertical wells among which three have NMR logs. The results reveal that subunits A1 and A2 differ significantly in petrophysical properties and reservoir quality. A2, the very fine-grained dolomitic sandstone subunit has larger pore size, higher porosity and permeability, lower shale content and water saturation, and thus represents the preferred interval for oil production across the Viewfield Bakken Pool area and has greater resource potential than the siltstone subunit A1. The mapped petrophysical properties show spatial trends that align well with the previously recognized regional geological features. Favourable potential high productivity zones can be outlined by the areas of intersection of all essential reservoir parameters above defined threshold values.