Abstract: Origin of Petroleum of Duran Oil Field -- Noroeste Basin, Argentina

Cerqueira, J. R. ? Petrobras/Cenpes; Schulz A. E. ? Tecpetrol

Geochemical analyses have been performed on two crude oil samples (Los Monos reservoir - Devonian - and Tupambi reservoir - Carboniferous/Permian) and two condensate samples (Las Peñas and San Telmo reservoirs - Carboniferous/ Permian) from the Duran oil field, located in Noroeste Basin, Argentina, with the aim of determining their source rock characteristics.

The geochemical composition of the oils were evaluated by high pressure liquid chromatography (HPLC), gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS and GC-MS/MS), carbon isotopic analysis of whole oils and of saturated and aromatic fractions and isotope ratio monitoring-gas chromatography-mass spectrometry (irm-GC/MS) of normal alkanes.

Geochemical properties, liquid and gas chromatography data, and carbon isotopic composition of the samples (table 1), would indicate that the Las Peñas and San Telmo condensates are more mature than Los Monos and Tupambi oils, but maturation parameters based on abb/abb+aaa C₂₉ steranes show that they have lower thermal evolution and different distributions of C₂₇, C₂₈ and C₂₉ steranes. Terpane analyses show that diahopanes are present in the oils and are absent in the condensates.

Analyses of light compounds of the oils and condensates (Fig. 1) indicate that the condensates are not a product of evaporative fractionation, but originated from kerogen cracking. These facts suggest that the condensates were generated by a different organic facies than that which sourced the oils.

The results indicated that Los Monos and Tupambi oils were generated by the organic facies present in the base of the Los Monos Formation (Devonian), which is predominantly amorphous. However, the condensates possibly had their origin related to the organic facies that occur in the upper and middle portion of the same formation with a predominance of liptinite and woody organic matter. There is a good correlation between geochemical analyses of the organic rock extracts of both intervals and of the oil and the condensates.

Table 1: Geochemical Properties of oils and condensates

Sample °API Sulfur Sat. Arom. NSO Pr/n d^aC Maturation Diahopanes

(%) (%) (%) (%) C₁₇ (?) abb/abb+aaa

L. Monos 40.9 0.041 77 17 6 0.17 -26.45 0.64 YES

Tupambi 48.1 0.022 74 16 10 0.17 -26.48 0.64 YES

Pescado 50.0 0.007 91 6 3 0.13 -26.46 0.62 YES

Las Peñas 59.3 0.003 82 9 9 - -26.17 0.52 NO

S. Telmo 62.9 0.003 92 3 5 - -26.32 0.57 NO

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil