Savanna Journal of Basic and Applied Sciences 2(1):41-52
Geochemical Characterization of Crude Oils from Tertiary Reservoir Units in Trinidad, Eastern Venezuela Basin
Abubakar, A. S. and Phillips, O. A.
ABSTRACT
Twelve crude oil samples from eight Tertiary reservoir units in Trinidad were analysed by using gas chromatography combined
with mass spectrometry (GC-MS)) to achieve their geochemical characterization. The specific objectives were to establish
genetic relationships between the oils; determine their maturity and source lithology; and unveil the environment of deposition
and extent of biodegradation. The biomarker characteristics established is an indication that the oils were generated from open
marine source rocks deposited in a reducing environment. This is consequent upon, the moderate pristane/phytane ratio (1.0-
2.0); carbon preference index (CPI) and odd over even preference (OEP) close to 1; low dibenzothiophene/phenanthrene ratios;
absence of 18α(H)-oleanane and; abundance of tricyclic terpanes. The oils are also characterised by high relative abundances
of regular steranes, diasteranae and hopanes compared to tricyclic terpanes and correlation between the set of analysed oils
also made possible. Overall, a single genetic type was established for the oils based on aliphatic and aromatic hydrocarbon
fractions contained. Biodegradation was clearly evident in the majority of samples analysed as demonstrated by the presence
of unresolved complex mixture and high Pr/nC17 and Ph/nC18 values. Thermal maturity assessment based on saturated and
aromatic hydrocarbon maturity parameters showed that the oils are at least marginally mature and corresponds to the early oil
generation window.
