Hydrocarbon Generation, Migration and Accumulation Related to Igneous Intrusions: An Atypical Petroleum System from the Neuquen Basin of Argentina

Felipe Rodríguez¹, Héctor J. Villar², and Roger Baudino^3
1Exploración Argentina Onshore, REPSOL-YPF, Talero 360 (8300) Neuquén, Argentina [email protected]
²Departamento de Ciencias Geológicas - FCEyN – Universidad de Buenos Aires - Conicet, Buenos.Aires, Argentina
³Gerencia de Exploración Brasil, REPSOL-YPF, Praia de Botafogo 300, 7 Andar (22250-040) Rio de Janeiro, Brasil

The stratigraphic record of the Altiplanicie del Payún area, in the Northern Platform of the Neuquén Basin, Argentina, includes Tertiary sills and laccolites that reach thicknesses of up to 600 m. Occurrence of thermally immature oil-prone shales of the Late Jurassic Vaca Muerta and the Hauterivian Agrio Formations is profusely documented in the area. However, when sills have intruded the Vaca Muerta shales, source rock sections become mature, displaying a wide-ranging maturity spectrum spanning thicknesses that exceed 400 m.

Commercial oil accumulations (20-33°API) and oil shows are found along the entire column, both in sandstone/carbonate reservoirs and fractured intrusives reservoirs. Oil-oil and oil-source rock correlations suggest a local generation related to the thermal effect of the intrusive bodies. Concurrently, diamondoid analyses point to mixtures of high-mature (cracked) with low-mature hydrocarbons: oils generated and cracked close to sills are considered to be mixed with oils generated from more distant source rock sections less affected by the thermal effect of the igneous bodies, as they migrate towards the sills and shallower reservoirs.

A 2D model that included the thermal effect of the three main igneous bodies of the area was satisfactory achieved, accounting for thermal maturation, oil and gas generation, migration and accumulation. From the modeling, hydrocarbons migration is favored by elevated generation pressures, source rock fracturing and convective water flows.

The integration of geochemical data and 2D-modeling of petroleum generation and migration related to the thermal effect of the igneous bodies led to the better understanding of this atypical petroleum system.

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands