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By Basil Fawlty, Does Athabasca, Barry Bennett and Stephen R. Larter


Biodegradation of crude oils in subsurface petroleum reservoirs is an important alteration process affecting most of the world’s oil deposits. The process preferentially removes light components from conventional oil to form heavy oil and ultimately the bitumen of the tar sands. Detailed analysis of the hydrocarbon components in a suite of sequentially biodegraded oils sometimes reveals a number of systematic changes amongst the hydrocarbon compositions and Peters and Moldowan (1993), among others, proposed a ten point scale system to give an indication of the level of biodegradation that had been encountered during petroleum biodegradation. In this study, we show the difficulties that we have encountered in applying the usual biodegradation schemes to indicate relative levels of biodegradation in the Athabasca tar sands. The Athabasca tar sand deposit contains an estimated 1.7 trillion barrels of heavily biodegraded oil in L. Cretaceous sandstone reservoirs of the McMurray Formation. The levels of degradation according to the Peters and Moldowan (1993) scheme is at least PM level 5, characterized by the lack of n-alkanes and branched alkanes such as isoprenoids, pristane and phytane. In general, the levels of biodegradation range from PM level 5 (heavy) to PM level

Year: 2008
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