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Thermal Maturity of Orange Basin Source Rocks: Insights from Aromatic Hydrocarbon Contents

Adekola, Solomon A.*1; Akinlua, Akinsehinwa 2; Mangelsdorf, Kai 3
(1) Department of Geology, Obafemi Awolowo University, Ile Ife, Nigeria.
(2) Fossil Fuels and Environmental Geochemistry Group, Department of Chemistry, Obafemi Awolowo University, Ile Ife, Nigeria.
(3) Previous HitHelmholtzTop Centre Potsdam GFZ, German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany.

Aromatic hydrocarbon distribution patterns have been evaluated for a series of thirty two Orange Basin source rocks of Cretaceous age using gas chromatography - mass spectrometry (GC-MS). The study concentrates on naphthalene and phenanthrene and their homologs. The distribution patterns of both naphthalenes and phenanthrenes are strongly controlled by thermal maturation. Thus, well developed aromatic hydrocarbon derived maturity parameters were used to evaluate the thermal maturity of the rock samples. The rock samples contain enhanced concentration of 1,2,5-trimethylnaphthalene relative to 1,2,7-trimethylnaphthlene that is typical characteristic of mature rocks. The methylnaphthalene ratios also indicate that the rocks are mature except for some Turonian age samples. Methylphenanthrene index and methylphenanthrene ratio show that thermal maturity increases with age (from Turonian to Early Aptian) and with depth.

The calculated vitrinite reflectance (Rc) values of most of the rock samples indicate thermal maturity in the oil window.


AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California