Biomarkers and Isotopic Characteristics of Crude Oils from a Central Niger Delta Depobelt Field, Nigeria

Twelve crude oils samples from a field in the central depobelt in the Niger delta, Nigeria were analyzed for their biomarkers and isotopic composition by Gas chromatography-Mass spectrometry and Isotope mass spectrometry. The percentage C-27,C- C-28 and C-29 steranes in the oils ranged from 35.80 to 39.9, 28.1 to 30.8 and 29.9 to 35.0, respectively. The distribution of molecular biomarkers and isotopic composition in the oils indicated that they were formed from source rocks of a mixed source (marine and terrestrial kerogen) but with greater input from marine organic matter. The Pr/Ph ratios of the oil samples ranged from 1.2 to 2.3 and this indicated organic matter deposited under suboxic conditions. The vitrinite reflectance (%VRc) values calculated from methylphenanthrene index-1 (MPI-1) parameter ranged from 0.89 to 1.07 indicating oils generated at the peak of oil window.