Regional McMurray Oil Sands Resource Characterization and Assessment, Athabasca Basin, Alberta

Thomas Nardin
T.R. Nardin Geoscience Consulting, Calgary, AB

From 1997 through 1999 Imperial Oil undertook a regional study, integrating well, core, seismic and outcrop data, to characterize and assess the Athabasca Basin's McMurray oil sands resource. Since that time, land postings and drilling activity in the basin have reached unprecedented levels. Currently, four industry SAGD (Steam Assisted Gravity Drainage) commercial projects, targeting approximately 10 GB of bitumen, are underway. Six additional projects are scheduled to start-up by 2010.

The McMurray Formation is a deepening-upward fluvial-estuarine succession with an estimated 500 GB of bitumen in place outside the mining area. Only about six percent of this resource appears to be amenable to SAGD recovery and consist of two principal reservoir types: braided stream and fluvial-estuarine point bars.

Reservoir facies and their trends are partially controlled by the Early Cretaceous fluvial drainage system. Laterally continuous, amalgamated braided stream sands occur within basal sequences along the north-trending McMurray Channel system and its tributary confluences. Fluvial-estuarine point bars overlie the basal section within the main channel and are the dominant reservoir type within tributary systems. Point bar reservoirs are smaller and laterally discontinuous; however, channel belt complexes can be prospective. Sand body geometries were extensively modified by erosion during McMurray sea-level lowstands.

The first-order control on reservoir fluid distributions is the Athabasca anticline. At the field scale, stratigraphic traps beneath high-relief unconformities commonly control the distribution of gas and top-water thief zones. Bottom water occurs within structural lows formed by salt dissolution, erosion, and karst development of subjacent Devonian carbonates.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005