Petroleum system, filling history and age appraisal of source rocks of the Niger Delta Basin: Fingerprinting of pentacyclic triterpenoids

Gas chromatography-mass spectrometry (GC-MS) was used to analyze the pentacyclic triterpenoid distributions, specifically hopane and oleanane fingerprints, in 24 crude oil samples from the Niger Delta depobelts, with the aim of defining the petroleum system, filling history, and the age of source rock producing these oils. The results indicate that the Niger Delta oils belong to a single fluvio-deltaic petroleum system, reflecting similar source organic facies and depositional environments. Geochemical parameters, including C₂₉/C₃₀ hopane ratios, oleanane index, Ts/Tm, (Ts/(Ts + Tm)), moretane/C₃₀ hopane ratios, and C₃₂ 22S/(22S + 22R) ratios, suggest oxic conditions during source rock deposition and thermal maturity of the oils. The presence of terrigenous organic matter and complex filling history are also evident and influenced by multiple phases of sedimentation, and petroleum generation. A comparative plot of geologic time (Paleogene-Neogene age) and oleanane percentage composition show that the crude oils are constrained to the chronostratigraphic ages of their respective depobelts, demonstrating the potential of oleanane-derived parameters for relative dating of hydrocarbon sources, complementing traditional index fossil methods.