Abstract: An Integrated Sequence Stratigraphy-Organic Geochemistry Study of the Vaca Muerta Petroleum Systems, Neuquen Basin, Argentina

M. E. Lara, D. A. Wavrek, R. Vines, G. A. Laffitte, S. Del Vo

This study shows that the Early Tithonian maximum flooding surface associated with the base of the Vaca Muerta Formation is an oil-prone marine condensed section which accumulated in the distal and shelfal parts of the basin during the maximum transgression. The overlying organic-rich sequences were deposited in a low-angle ramp setting in response to minor relative sea-level changes within an overall relative stillstand. Throughout the basin, the TOC content of the Vaca Muerta Formation decreases upward with the maximum TOC values correlating to the basal condensed section.

Lateral variations in depositional setting along the Neuquen Embayment correlate to different source facies within the Vaca Muerta Formation. The distal source facies consist of multiple stacked marine condensed depositional sequences of all systems I tracts. The upward decrease in TOC of the distal facies is gradual indicating that prolonged sediment starvation resulted in the accumulation of a thick organic-rich section. However, expulsion efficiency from the distal source facies was relatively low as it required high levels of thermal stress.

The shelfal source facies consist of a single marine condensed section whose TOC content abruptly decreases upward due to the diluting effect of clastic highstand progradation. The low-angle shelfal setting favored widespread accumulation of the relatively thin shelfal facies, but coarser sediment interbedding increased expulsion efficiency from this facies. Kimmeridgian-incised valleys provided a regional migration pathway for hydrocarbons generated from both the distal and shelfal source facies.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela