Assessment of Thermal Maturity of Crude Oils Using Biomarker Fingerprinting

Abstract

The study assesses the thermal maturity levels of crude oils from the Niger Delta Basin of Nigeria using biomarker fingerprinting technique. Thirteen (13) crude oil samples were deasphaltened by the addition of n-heptane. The maltene fractions were analysed using the Gas Chromatography-Mass Spectrometer (GCMS) in Selected Ion Mode (SIM) to obtain the biomarker chromatograms. The respective biomarker thermal maturation peaks were extracted and their ratios computed. The odd to even predominance (OEP) and carbon preference index (CPI) values vary from 0.94 to1.08, with an average value of 1.02 and 1.01 to 1.12, with a mean value of 1.07 respectively. The ratios of Pr/n-C17 and Ph/n-C18 for the samples vary from 0.44 to 1.04, with a mean value of 0.73 and 0.53 to 0.77 with a mean value of 0.63, respectively. The Ts/Tm ratio ranges between 0.56 to 1.25. The Ts/(Ts+Tm) ratio ranges from 0.36 to 0.56. The C32 22S/(22S + 22R) hopane ratios for the samples range between 0.53 to 0.58. The C29 sterane maturity ratios 20S/(20S + 20R) and ββ/(ββ+αα), vary from 0.33 to 0.56 and 0.34 to 0.67, respectively. The estimated biomarker maturation parameters suggest the analysed samples reached and or exceeded the peak of the oil generation window, with high levels of thermal maturity.