Spatial-Temporal Evolution of Channelized Depositional Systems in the Cretaceous McMurray Formation, Alberta, Canada: Implications for Delineation of Oil Sands Reservoirs

Abstract

The McMurray Formation of northeastern Alberta represents the principal bitumen reservoir within the Athabasca Oil Sands Region (AOSR). Economically recoverable reserves are hosted exclusively within sandstone-dominated, channelized geobodies (i.e., valley fills or channel belts) distributed amongst regional coarsening upward packages bound by flooding surfaces. Using a vast, publically available dataset of well logs (n=2800) and cores (n=55), we develop and apply an updated stratigraphic framework across a vast portion of the southeastern AOSR (5,700 km²) in order to: (1) document the stratigraphic evolution of drainage systems; and (2) compare and contrast the stratigraphic architecture and facies distribution of four distinct channel trends, which account for all of the major reservoir fairways defined in the study area.

Regional 3D models and petrophysical maps are constructed to evaluate the external geometries and internal fill characteristics of the channelized systems. Detailed facies analysis and sand distribution maps within several of these systems reveal a fundamental shift of internal architecture and sedimentary styles through McMurray Formation deposition. Earlier depositional systems are characterized by overall west-to-east oriented tributive channel belts or valleys, with complicated internal fills largely consisting of amalgamated fluvial point-bar deposits. In contrast, the youngest mapped drainage system is characterized by a distributive geometry, and its internal fill is dominated by clean sandstone. Significant variation in reservoir heterogeneity among these systems is readily apparent, and related to either: (1) shifts in the relative balance of fluvial and marine processes that are imparted on the channel settings; or (2) variations in the degree of meanderbelt confinement amongst the systems, which is associated with heterolithic counter point-bar and oxbow lake deposits. While the older McMurray channel systems can be ascribed to fluvially dominated systems, the latest McMurray channel system records a deviation from fluvial to tidal domination. This transition is reflected by a departure from heterogeneous stratified point-bar deposits, to homogeneous sand bars lacking laterally extensive muds beds. The varied distribution of mudstone beds has a significant impact on the implementation of steam-assisted bitumen recovery methods.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018