PETROPHYSICAL AND GEOMECHANICAL RESERVOIR MODELS FOR DEVONIAN SHALE RESERVOIRS IN WESTERN CANADA FROM DETAILED FACIES ANALYSIS (Invited Presentation)

Upper Devonian shale formations in western Canada are targets for hydrocarbon exploration and development, including the Horn River Group in northestern British Columbia, and the Duvernay Formation in Alberta. Numerous long cores and additional wells with electric logs have enabled us to develop detailed depositional and sequence stratigraphic models for both units. Depositional facies and stratigraphic sequences are then related to geochemical composition, from which we deduce paleoenvironmental parameters and biogenic production. Finally, we relate facies and composition to petrophysical and geomechanical properties.

Late Devonian paleogeography in western Canada was dominated by carbonate platforms and isolated reefs with mudstones in intervening basins. Bioturbation, benthic body fossils and trace element geochemistry distinguish sedimentary facies deposited in anoxic and dysoxic to oxic settings. Anoxic facies are most enriched in organic carbon and dominated by biogenic silica or carbonate minerals; much of the sediment was deposited through suspension settling. Dysoxic to oxic facies are bioturbated, contain less organic carbon and more clay and were deposited by sediment gravity flows and contour currents. Transitional facies are locally present. Anoxic facies are more widespread in transgressive systems tracts and are abundant in distal locations. Dysoxic to oxic facies are more widespread in lowstand and falling-stage systems tracts and are more common in settings near basin margins.

Brittleness and hardness are strongly related to clay content; increasing clay content results in more ductile formation, whereas carbonate and biogenic silica produce a harder formation. Because rock composition is controlled by paleogeography and sequence stratigraphy, geomechanical properties can be spatially and stratigraphically predicted. Petrophysical properties are less strongly related to rock composition, because several primary and secondary porosity types are present and because thermal maturity exerts a control. A weak positive correlation between total organic carbon and total porosity was observed. Matrix permeabilities are clearly related to permeability with a strong positive correlation.