Abstract

TOMAS, Germán  and  ACUNA, Adrián. Biomarkers applied to the study of crude oils extracted from the Magallanes Formation, Austral Basin, Argentina. Bol. Soc. Geol. Mex [online]. 2022, vol.74, n.1, e160621.  Epub May 02, 2023. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2022v74n1a160621.

In the stratigraphic column of the Austral basin, there are several units that behave as reservoir rocks, and one of them is the Magallanes Formation. Its lithological characteristics make it a unit of interest for the definition of the petroleum systems in the basin. For this reason, the organic geochemical biomarkers: saturated (n-paraffins, acyclic isoprenoids pristane and phytane, steranes and terpanes) and aromatic (naphthalenes, phenanthrenes and dibenzothiophenes) were evaluated in five crude oils from two Magallanes Formation reservoirs in order to establish their precursor organic matter type, the thermal maturity degree and, the lithology and depositional conditions that controlled the accumulation and preservation of organic matter in their source rock. The crude oils were subjected to separation of their aliphatic and aromatic fractions by solid-liquid adsorption column analyzed each one by gas chromatography-mass spectrometry (GC-MS). From the diagnostic ratios, calculated with the relative abundances of the biomarkers, it is suggested that the organic matter source (mixed marine-continental), were deposited in a sedimentary environment with moderate-to-low oxygen concentration (disoxyc-suboxyc), in which the source rock was characterized as marine and siliciclastic in nature (delta dominated shelf shales). The only difference was observed in the crude oils thermal maturity, with the Agua Fresca being mature and the María Inés located on the borderline between mature and over-mature. The experimental evidence suggests a thermal maturation process over Maria Inés crude oils in their reservoir.

Keywords : biomarkers; organic-matter; Magallanes Formation; Austral basin; Argentina.