Olivier Galland

This contribution presents a detailed geological study of a well-exposed igneous petroleum system at Sierra de Cara Cura, Neuquén Basin, Argentina, which consists of sills, dykes, laccoliths and hybrid intrusion morphologies. The size of the exposed intrusive complex (19 km in north–south direction) is similar to those of sill-clusters hosting producing oil fields of the nearby Río Grande Valley. Most sills (>80%) are preferentially emplaced in the organic-rich rocks such as Vaca Muerta and Agrio Formations. Sills are extensively fractured and represent potentially good fractured hydrocarbon reservoirs. We document several fracturing mechanisms that can lead to heterogeneous fracture distribution. Laccoliths represent very different igneous reservoirs with a typical zonation: the core of the laccoliths are massive and poorly fractured, whereas the rims consist of a breccia formed during laccolith emplacement. The Vaca Muerta and Agrio Formations are thermally altered by the cooling of the sills. The deep parts of the outcropping laccoliths likely altered thermally the shale formations they were emplaced in. Hydrogen Index (HI) and Transformation Ratio (TR) of the organic matter are the best parameters to determine the thickness of the thermal aureole. The Sierra de Cara Cura appears as a world-class field analogue of igneous petroleum systems.