TRAZADORES DIAGENÉTICOS DE LAS PALEOMIGRACIONES DE HIDROCARBUROS EN LAS ARENISCAS ROJAS CRETÁCICAS DEL GRUPO NEUQUÉN, CUENCA NEUQUINA

FRANCHINI MARTA; ANA LAURA RAINOLDI; JOSEFINA PONS; ADOLFO GIUSIANO; AGNES IMPICCINI,; CESARETTI NORA; DANIEL BEAUFORT; PATRICE PATRIER

Mendoza

Congreso; XIX Congreso Geológico Argentino IX Congreso de Exploración y Desarrollo de Hidrocarburos; 2014

Diagenetic tracers of hydrocarbon paleo-migratios in Cretaceous red beds of the Neuquén Group, Neuquén Basin Striking arrangement of colorful facies in the sandstones outcrops of the Candeleros, Huincul,And Portezuelo formations at Los Chihuidos high (Neuquén Group) and at the Huincul Ridge has been attributed to the surface expression of hydrocarbon-induced alteration. According to visual distinctions, four diagenetic facies have been recognized: red, white, gray, and brown sandstones. Differences in the mineralogy between sandstones facies depend on the degree of interaction with hydrocarbon-bearing solutions and the relative position of the redox roll front developed during this process. The red facies represents the original oxidized sandstones withhematite, kaolinite or corrensite, quartz and albite overgrowths, and calcite cement precipitated under oxidizing conditions during the regional burial diagenesis. The white facies formed during the interaction of red beds with hydrocarbons-organic acids, where clasts and cement were partially dissolved, iron was reduced to Fe2+ and removed or precipitated as pyrite, resulting in the sandstone decoloration and in a notorious enhancement of the secondary porosity. Only minor montmorillonite precipitated replacing kaolinite and detrital feldspars and multistage calcite filling the pores. The gray and the brown sandstones locally bound the redox front with abundant clay and oxide minerals. Montmorillonite and secondary hematite are dominant in the more oxidized gray sandstones whereas interstratified chlorite-montmorillonite is more abundant in the more reduced brown sandstones. The coexistence of these minerals indicates metastable reducing-oxidizing conditions at the redox front. This multi-scale study of patterns of bleaching in a succession of clastic rocks allowed the definition of a redox system at regional scale linked to structure controlled upflow of hydrocarbons and associated fluids, and the chemical reactions between reducing fluids