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

FRANCHINI M.; RAINOLDI A. L.; PONS M.J.; GIUSIANO A.; IMPICCINI, A.; CECARETTI N.; BEAUFORT D.; PATRIER P.

Mendoza

Congreso; IX Congreso de Exploración y Desarrollo de Hidrocarburos; 2014

IAPG

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 with hematite, 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 and diagenetic minerals.