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Western Canada Sedimentary Basin
Use of Biomarker Geochemistry to Identify Variable Biodegradation Levels, Cold Lake Oil Sands (Fort Kent Area), Alberta
Located in the Cold Lake oil sands area, the Fort Kent thermal project of Suncor Inc. (Twp. 61, Rge. 4W4) has 171 closely spaced boreholes penetrating the Upper Mannville Group (Lower Cretaceous). Cores are available from fourteen of these boreholes. We have conducted organic geochemical studies of five bitumens from the Sparky, Waseca, and McLaren formations. Distributions of the terpane and sterane biological markers show a) no evidence of biodegradation of these compound classes, and b) that the five samples are virtually identical both in individual components and ratios among those components. This suggests a common source for these bitumens. Other biomarker ratios indicate that all five samples are at a similar moderate level of thermal maturity. Although the five samples are not extensively biodegraded as compared to, for example, the Athabasca oil sand bitumens, saturate fraction gas chromatograms (SFGC) demonstrate that there are differences in the degree of biodegradation among samples. These differences can be quantified using biomarkers. For example, the amount of pristane versus hopane decreases with increasing biodegradation since hopane is more resistant to microbial degradation. This ratio, plus the ratios pristane × 1000/(total SFGC signal), and hopane × 1000/(total SFGC signal), provide a quantitative measure of biodegradation. The only obvious control on the biodegradation of these samples is that of grain size of the host sands. Thus, a single sample from a very fine grained Waseca Formation tidal channel deposit is least biodegraded; two samples from Lower McLaren Formation incised, fine grained sand, channel-fill deposits are moderately biodegraded; and two samples from the fine to medium grained, regionally developed sands of the Lower Waseca and Sparky formations are most biodegraded.
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