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Eugenio Santos Neto1, José Cerqueira1, Tikae Takaki1, Previous HitAlainTop Prinzhofer2

(1) PETROBRAS/CENPES, Rio de Janeiro, Brazil
(2) French Institute of Petroleum, Rueil-Malmaison, France

ABSTRACT: Ponta Grossa-Itararé: An Unusual Gas System in the Paraná Basin, Brazil

Petroleum systems in the Paraná Basin are very complex to explore due to the geological peculiarities of this basin, especially because of the thermal influence of igneous intrusions on maturation of the source rocks.

Recently, the wells drilled in the central-southern area of the basin have revealed good potential for gas. Those gas accumulations have similar chemical compositions with methane, ethane, propane, iso- and n-butane representing approximately 90%, 5%, 0.2%, 0.2%, respectively.

Carbon isotopic compositions of ethane and propane, -33o/oo vs. PDB, are compatible with the relatively 13C-depleted sources of the Ponta Grossa shales (Devonian). However, methane has an anomalous enrichment in 13C relatively to C1-C4 fraction suggesting higher levels of thermal maturity. Such chemical and isotopic signature is typical of a mixing of hydrocarbons generated under variable levels of thermal stress influenced by direct heat from igneous intrusions.

The relationship between the carbon isotopic compositions of ethane and propane versus ethane/propane ratio suggest that secondary cracking, of preexisting hydrocarbons, was significant to this gas system.

The objectives of this study are to characterize geochemically the gas produced from the Itararé and Rio Bonito formations in the central-southern part of the Paraná Basin, and to infer their sources and possible secondary alterations.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado