Abstract

Most of the bitumen resources in the Athabasca oil sands area are contained in fluvial and estuarine channel deposits of the Lower Cretaceous McMurray Formation. Stratigraphic sections were measured along a 5 km stretch of the Steepbank River, north of Fort McMurray, near the Suncor Steepbank Mine. We have identified at least four channel complexes based on stratal bounding surfaces, arrangement of exposed lithofacies, and consistent paleoflow patterns. The lower part of each channel complex contains medium to large-scale, trough crossbedded sandstone, exhibiting high porosity and permeability. These sandstones were deposited in channel axes and are the highest-grade bitumen deposits in the study area. Overlying inclined beds (sandy or muddy inclined heterolithic stratification) downlap on the lower sandy beds and were deposited in estuarine point bars, but the permeability and bitumen saturation of these strata are considerably lower.

Nearby wells contain cored and logged intervals that are similar to exposed outcrops in the riverbank. For the outcrop sections, artificial sonic logs were constructed by comparison with sonic curves from these nearby wells, but the curves were modified to reflect differences in thickness and mud content at the exposure. Three structural-stratigraphic cross-sections and ray-tracing techniques were used to construct seismic models. These models compare favourably with four high-quality, industry-acquired seismic lines from the Clarke Creek Exxon Mobil lease area, about 20 km southeast of the Steepbank River outcrops. The deposits at Steepbank are thus similar in scale and geometry to those in the Clarke Creek area. The Clarke Creek channel complexes are very well imaged on the seismic profiles, and our seismic modeling indicates that high-resolution seismic data are necessary to image these channels.

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