2α-Methylhopane: Indicator for Oil–Source Correlation in the Pearl River Mouth Basin, China

Oil samples collected from the Pearl River Mouth Basin (PRMB) were analyzed using comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC?×?GC-TOFMS). High abundances of compounds in the 2α-methylhopane series were observed and accurately quantified. Although the 2α-methylhopane series can be a prominent biomarker in the oil and source rock samples, it has generally been used less than non-methylated hopanes. In this study, the 2α-MHI [C₃₁2α-methylhopane?×?100/(C₃₁2α-methylhopane?+?C₃₀-αβ-hopane) (%)] ranges from 0.81 to 5.77% and 9.06 to 23.93% in Enping Formation- and Wenchang Formation-derived oils, respectively. The high abundance of the 2α-methylhopane series in Wenchang Formation-derived oils is attributed to anoxygenic phototrophs. The relevant 2α-methylhopane parameters showed correlations with C₃₀-4-methyl steranes/∑C₂₉ steranes, Pr/Ph and bicadinane-T/C₃₀-αβ-hopane. Furthermore, the 2α-methylhopane series are rich in middle-deep lacustrine environments as well as marine sedimentary environment. The results indicated that the 2α-methylhopane series could be used as effective biomarkers to distinguish oils derived from different source rocks, as well as to enlarge the PRMB biomarker assemblages, which is beneficial to the evaluation of petroleum resources.