Lithofacies-dependent pore-throat radii and reservoir properties in the Lower Triassic Montney Formation, Puskwaskau Field, Alberta

The reservoir quality of the Lower Triassic (Induan-Olenekian) Montney Formation of the Puskwaskau Field is assessed from two cored intervals. Four lithofacies are identified in the present study: these are defined by their detailed sedimentological characteristics. Lithofacies 1 (L-1) is composed of interlaminated bituminous very fine-to medium-grained siltstone and dolomitic medium-to coarse-grained siltstone. Lithofacies 2 (L-2) consists of interbedded dolomitic medium-to coarse-grained siltstone and bituminous very fine-to medium-grained siltstone. Lithofacies 3 (L-3) is dominated by bitumen-stained dolomitic medium-to coarse-grained siltstone. Lithofacies 4 (L-4) is characterized by dense, dolomitic coarse-grained siltstone to very fine-grained sandstone. Sediments within the study area are interpreted to have been deposited within a wave-to storm-influenced shoreface and offshore transition zone, comprising conformable progradational successions. The reservoir quality of these deposits is evaluated by comparing reservoir characteristics of each lithofacies. Analyzed properties include porosity, permeability, pore throat radius, clay content and cementation. Winland plots are used to show the predicted pore-throat diameters of lithofacies based on measured permeability (to air). The reservoir quality of L-1 is poor, with pore-throat radii ranging from 0.10 to 0.45 μm (micropores). The reservoir quality of L-2 is considered fair, with pore-throat radii ranging from 0.11 to 0.94 μm (micro- and mesopores). L-3 has the best reservoir quality in this study, with pore-throat radii ranging from 0.20 to 3.01 μm (mesopores). The reservoir quality of L-4 is considered poor due to pervasive dolomite cementation. Pore-throat radii for L-4 range from 0.17 to 0.25 μm (micropores). The range of values observed within each lithofacies effectively constrains the reservoir characteristics and demonstrate the correspondence of lithofacies classification to reservoir quality in this producing field.