Igneous Reservoirs in Triangle Zones, Neuquen Basin, Argentina

H. J. Belotti, L. O. Rebori, G. H. Ibanez

Important oil and gas fields in the Neuquen basin were discovered in the external zone of the Subandean fold-and-thrust belt over the last decade. This zone is characterized by thin-skinned deformation generating triangle zones. The lower detachment of the tectonic wedge is in the base of the Mendoza Group (Upper Jurassic Vaca Muerta Formation) and the upper detachment is in the Lower Cretaceous Huitrin Formation.

Reservoirs in the triangle zones consist of sandstones of the Avile Member (Lower Cretaceous Agrio Formation) and the Troncoso Member (Huitrin Formation), and fractured carbonates of the Lower Cretaceous Chachao and Mulichinco formations and the Chorreado Member (Huitrin Formation). The Filo Morado, El Porton, and Puesto Rojas oil and gas fields are good examples of these types of accumulations.

Where the triangle zones involve distal facies of the Mendoza Group, as in the Sierra Azul, the conventional reservoirs are absent. However, east of this triangle zone, the oil production comes from Miocene to Oligocene igneous rocks in the Los Cavaos, Malal del Medio, and Rio Grande fields. Here hydrocarbons are contained in fractures and microvugs of andesitic sills that intruded the Mendoza Group shales. These andesitic sills could be a new exploration play in the triangle zones where conventional reservoirs are absent.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995