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AAPG Bulletin

Abstract

AAPG Bulletin, V. 99, No. 3 (March 2015), P. 525ndash554.

Copyright copy2015. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/08131413170

Mineralogical signature of hydrocarbon circulation in Cretaceous red beds of the Barda González area, Neuquén Basin, Argentina

M. J. Pons,1 A. L. Rainoldi,2 M. Franchini,3 A. Giusiano,4 N. Cesaretti,5 D. Beaufort,6 P. Patrier,7 and A. Impiccini8

1Consejo Nacional de Investigaciones Científicas y Técnicas; Centro Patagónico de Estudios Metalogenéticos, Universidad Nacional del Comahue, Buenos Aires 1400, CP8300, Neuquén, Universidad Nacional de Río Negro, Argentina; [email protected]
2Consejo Nacional de Investigaciones Científicas y Técnicas; Centro Patagónico de Estudios Metalogenéticos, Universidad Nacional del Comahue, Buenos Aires 1400, CP8300, Neuquén, Universidad Nacional de Río Negro, Argentina; Departamento de Geología, Universidad Nacional del Sur, Bahía Blanca, Argentina; [email protected]
3Consejo Nacional de Investigaciones Científicas y Técnicas; Centro Patagónico de Estudios Metalogenéticos, Universidad Nacional del Comahue, Buenos Aires 1400, CP8300, Neuquén, Universidad Nacional de Río Negro, Argentina; [email protected]
4Dirección Provincial de Hidrocarburos y Energía de la Provincia del Neuquén, Argentina; [email protected]
5Departamento de Geología, Universidad Nacional del Sur, Bahía Blanca, Argentina; [email protected]
6Université de Poitiers, IC2MP, CNRS-UMR 7285, Hydrasa, Bâtiment B08, Rue Albert Turpin, F-86022 Poitiers Cedex, France; [email protected]
7Université de Poitiers, IC2MP, CNRS-UMR 7285, Hydrasa, Bâtiment B08, Rue Albert Turpin, F-86022 Poitiers Cedex, France; [email protected]
8Centro Patagónico de Estudios Metalogenéticos, Universidad Nacional del Comahue, Buenos Aires 1400, CP8300, Neuquén, Universidad Nacional de Río Negro, Argentina; [email protected]

ABSTRACT

The Portezuelo Formation is part of a red bed sequence in the Neuquén Basin assigned to the Neuquén Group (lower Cenomanian–middle Campanian). In outcrops of the Portezuelo Formation in the Barda González region, iron oxide and hydroxide cements are only preserved in the less permeable claystone layers. Paleomigration of hydrocarbons and formation waters along the most permeable layers bleached the rocks due to partial to total dissolution of cements and grains and formation of several authigenic minerals: (1) montmorillonite and pyrite in the medium- to fine-grained sandstones and mudstones, and (2) multistage calcite and pyrite in the coarse-grained sandstones and conglomerates. The BLTN13170eq1 (Canyon Diablo troilite) of −24.4 to −60‰ values in pyrite point to microbial reduction of a sulfate precursor. The oxidation of hydrocarbons and fluctuations in pH and carbon dioxide pressure caused by organic acids resulted in multiple stages of dissolution and precipitation of calcite. Calcite crystals host hydrocarbon-bearing fluid inclusions (± pyrite) with variable fluorescence color, indicating that hydrocarbon composition changed with time. The intermediate BLTN13170eq2 (Peedee belemnite) (−8.11‰ to −8.52‰) and BLTN13170eq3(−9.76 to −9.83‰) isotope composition of calcites may have resulted from mixtures of BLTN13170eq4-rich BLTN13170eq5 after the dissolution of local calcrete with BLTN13170eq6-poor BLTN13170eq7 from oxidizing hydrocarbons.

This contribution provides for the first time key information to predict the distribution of authigenic minerals in reservoir rocks in the basin and improves understanding of the diagenetic history of the Portezuelo Formation.

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