oa Significance of 3’-Methyl-1,2-Cyclopentenophenanthrene in Characterization of Crude Oils (Se Pannonian Basin, Serbia)

C20, C21 and C26-C28 triaromatic steroids are widely used in investigations of sedimentary organic matter. On the other hand, C18 triaromatic steroid, 3’-methyl-1,2-cyclopentenophenanthrene has attracted much less attention. During investigation of crude oils from the most important oil fields in Serbia (SE Pannonian Basin), considerable concentrations of 3’-methyl-1,2-cyclopentenophenanthrene (MCpP) were observed in the total ion chromatograms of aromatic fractions. Therefore, the objective of this study is to establish applicability of MCpP in characterization of crude oils. A novel maturity parameter MCpP index: MCpPI = 10 × MCpP/(MCpP+SC26-C28 (S+R) triaromatic steroids) is proposed. It showed statistically significant correlations with common maturity ratios, and proved its applicability in wide range of maturity, Rr=0.60–1.05%. The typical values of MCpPI at different maturity levels are as follows: < 0.50 for early mature oils (Rr = 0.60–0.67%), 0.75–1.30 for moderately mature oils (Rr = 0.70–0.80%), 1.40–2.30 for mature oils (Rr = 0.85–0.95%), and > 2.50 for very mature oils (Rr = 0.95–1.05%). The MCpPI can be used up to the 4th stage of biodegradation. Another defined parameter is the 2-methylphenanthrene/MCpP ratio, which is particularly applicable at higher maturities, but can be used only for oils which did not exceed the 2nd stage of biodegradation.