Summary
The Vaca Muerta – Quintuco system is composed of dark, fine-grained, organic-rich mudstones, marlstones and limestones. This marine succession (Tithonian-Valanginian) is located in the Neuquén basin of western Argentina and was deposited in a restricted, low energy, back-arc setting (proto-Andes) with a predominant direction of progradation from southeast to the northwest . Compression during the Cenozoic associated with the Andean Orogeny uplifted the western portion of the basin, whereas the eastern portion remains in subsurface as one of the country's most productive oil and gas basins .
Regional seismic lines (100–180 Km) from proximal to distal facies (southeast to northwest), show a strongly regressive stacking pattern for the Vaca Muerta interval. When analyzed in detail, the succession can be divided into at least 5 major transgressive-regressive packages or depositional sequences with distinctive seismic stacking patterns. The base is marked by a regional flooding event overlain by prograding clinoforms with well-defined topsets (Quintuco), foresets, and bottomsets (Vaca Muerta) in the proximal and central areas of the basin (mostly subsurface). However, as we move northwest into the distal facies (subsurface and outcrops), most of the Vaca Muerta interval is characterized by parallel reflectors (railroad tracks) due to the distal stacking of multiple clinoform bottomsets, which results in a much thicker organic-rich section (~350m) than in proximal areas (~150m).
Based on the analysis of cores, well data, biostratigraphy, petrophysics, and geochemistry in distal facies of Vaca Muerta, in addition to regional 2D/3D seismic data, we were able to correlate (chronostratigraphically) distal facies of Vaca Muerta to proximal basin-margin settings. As a result, we created a predictive sequence stratigraphic model to explain lateral and vertical changes in facies, total organic carbon (TOC), and mineralogical composition. The combination of seismic stratigraphic and geomorphic techniques allowed regional interpretations for depositional systems, slope-break delineation, direction of progradation, and mapeable facies belts, all of which provide a basis for reservoir prediction, lithology distribution, and sweet spot identification for unconventional exploration. Additionally, the thermal maturity along the depositional dip ranges from "early oil" window in the east to "dry gas" in the west with cross-cutting relationships to facies belts. A clear understanding of these relationships is critical in defining reservoir property maps and regional basin play concepts.
