Reservoir characterization of channel-belt strata, McMurray Formation, northeastern Alberta

Abstract

The reconstruction of stacked channel-belt strata provides important insights into the heterogeneity that results from fluvial depositional processes over a range of spatial and temporal scales. The Lower Cretaceous McMurray Formation of northeastern Alberta represents one of the world’s most significant bitumen reserves, which is hosted in part, within fluvial strata. An extensive subsurface dataset, including production data, is used in this study to characterize stacked channel-belt deposits and demonstrate the impact of numerous scales of heterogeneity on reservoir quality and performance. Bed- through bar- and channel-belt-scale investigations of the McMurray Formation are numerous, however almost all previous studies have overlooked the impact of vertically stacked meander-belt deposits on heterogeneity delineation and production performance. This is a consequence of the difficulty in readily mapping older channel-belt units, which are partially eroded and unresolvable in seismic data. In this study, the delineation of channel-belt remnants that persist beneath the youngest, seismically-defined fluvial system, is achieved. A novel approach to mapping these units relies on: (1) correlating a recently-refined stratigraphic framework into the study area, and in particular, beneath the well-characterized upper channel-belt strata; (2) fine-scale focus of underlying units to define criteria to distinguish vertically stacked channel-belts, including changes in facies, bioturbation type and intensity, sandstone content, grain size, and dip azimuth of dipping strata, which help to define belt boundaries; and (3) the use of preserved parasequence elevations in combination with sub-Cretaceous unconformity paleotopographic elevations, which help identify restricted areas of potential channel-belt development at each stratigraphic level. We show that heterogeneous boundaries between belts, as well as differing stratigraphic architecture amongst successive channel systems, significantly impacts production performance. It is clear that detailed characterization of stacked channel-belt strata at the outset of a project could have a profound impact on their performance and long-term viability.