Geochemical Study of Crude Oil Samples to Evaluate Extent and Effect of Secondary Alteration Process (i.e. Biodegradation).

Abstract- A mild chemical treatment i.e. Ruthenium ion catalysed oxidation (RICO) has been employed to examine the asphaltenes of two oils (fresh and slightly degraded) chosen from four oils samples after bulk geochemical analysis. The oils were from same geographical location but unknown oilfield in North America. The distributions of hopanoic acids released from the asphaltenes were investigated and compared with that of hopanes in the maltenes. The distributions were dissimilar e.g. distribution of carbon number maximized at C32 in the terpenoic acids which are not consistent with that of terpanes (hopanes) in the maltenes. However, C29 and C30 hopanes were the prominent in the maltenes where as C32 hopanoic acids homologues in the released products. Comparatively, biodegradation was inferred to have no effect on the bonded biomarkers due to their unaltered nature after RICO treatment. Concomitantly, the difference and level of degradation between the samples were also investigated and found to be small (insignificant) with minor or no loss of n-alkanes or any other biomarkers in the samples. Although, samples 6661 and 8673 were slightly degraded and ranked “1 ” in the Peters and Moldowan (1993) scale, still none of the sample appeared to have lost their isoprenoids, hopanes and steranes. This indicates that the samples were slightly biodegraded. On the other hand, oils (8673 and 8676) were ranked “0 ” on the same scale indicating that they are not degraded