Impact of Biodegradation on Heavy Oil Compositions of the Peace River Tar Sands, Alberta

Jennifer Adams, Geology and Geophysics, University of Calgary, Calgary, Alberta; [email protected]

Most remaining petroleum resources have been altered by biodegradation in the subsurface making the oil more difficult to produce and more costly to refine. In Alberta, the genesis and key aspects of biodegradation of the tar sands are poorly constrained, despite being one of Earth’s largest petroleum accumulations. An understanding of the nature and rates of the biodegradation processes that produced these tar sands may elucidate the charge history and source rocks, facilitate prospect selection for future exploration or enhanced production and help define viscosity sweet spots in the tar sand environment.  The northeastern Peace River oils exhibit steep gradients of decreasing API gravity, and increasing viscosity towards the oil-water contact, which we attribute to active oil biodegradation.  Three vertical oil-saturated cores through the Peace River tar sands will be sampled for geochemical analysis. All samples will be analyzed (Iatroscan) for basic oil compositions to select 20 to 30 samples for gas chromatography and gas chromatography-mass spectrometry analysis for saturated and aromatic hydrocarbons and non-hydrocarbons. Biodegradation rates for a suite of oil compound classes in Peace River tar sands reservoirs will be derived using geochemical characterization of compositional gradients in these tar sand oils and calibrating one-dimensional numerical models of oil charging and degradation with these data.  Basic charge modelling will estimate the sensitivity of degradation rates to the underlying water column height and temperature.  In addition, the detailed geochemistry will be used to do oil-source rock correlations, which will inform timing estimates for maturation and migration.