Integrating sedimentology and ichnology with rock typing and flow units: Implications for clastic reservoir characterization

Abstract

Shallow marine clastic reservoir facies prediction, correlation, distribution, thickness, and quality remains a challenge. This study integrates sedimentology and ichnology with reservoir rock typing and flow units to characterize the Lower Cretaceous Wabiskaw Member reservoir. An integrated geologic depositional model is presented using sedimentological data (rock types, sedimentary structures, grain size), ichnological data (trace fossils intensity, size, diversity), reservoir characteristics (porosity, permeability), and well log data. The Wabiskaw Member strata are characterized using four facies associations (composed of nine sedimentary facies). Facies association 1 (FA-1) comprises dark grey to blue-grey mudstone with a distinctly lenticular appearance (Facies 1, 2). Ichnologically, a stressed archetypal Cruziana Ichnofacies represent FA-1. Facies association 2 (FA-2) is fine-lower medium-grained sandstone with thin mudstone interbeds (Facies 3, 4). A stressed ichnological suite of mixed Skolithos-Cruziana Ichnofacies is present in FA-2. Facies association 3 (FA-3) is dark grey to bluish-grey mudstone with minor sandstone interbeds (Facies 5, 6). Trace fossils of archetypal Cruziana Ichnofacies are present in FA-3. Facies association 4 (FA-4) comprises upper fine to lower fine glauconitic sandstone (Facies 7, 8, 9) with a high-density trace fossil assemblage. FA-1 and FA-2 represent deposition in a wave-influenced prodelta to delta front settings, whereas FA-3 and FA-4 represent deposition in the offshore-shoreface environment. The reservoir quality of various reservoir facies (F-3, F-4, F-7, F-8) is evaluated by comparing facies reservoir characteristics (porosity, permeability, pore throat radii, flow-storage capacity, oil saturation, and thickness). F-4 is the best and most productive reservoir (pore throat radius >20 μm, 18% flow, and 4% storage capacity) in the study area. F-7 is ranked second-best in reservoir quality based on petrophysical characteristics (pore throat radius between 10 and 20 μm, 36% storage 47% flow capacity). F-8 is ranked third in reservoir quality with pore-throat radii ranging from 4 to 10 μm (mesoporous), 23% storage, and ≤5% flow capacity. F-3 is ranked last amongst the Wabiskaw Member reservoir facies. It is micro-porous (pore-throat radii ranging from 2 to 4 μm) with 37% storage and ≤5% capacity flow.