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Mapping of TOC rich intervals in the Vaca Muerta Formation


The Vaca Muerta Formation is the Late Jurassic - Early Cretaceous basal component of a time-transgressive prograding shelf system. Due to the prograding nature, and evolving fill of the basin, deposition of strata rich in Total Organic Carbon (TOC) is variable laterally, while temporally constrained.

The variability of organic-rich strata in outcrops and subsurface displays an increase towards the basin center. Extensive sampling (~4000 outcrop and subsurface samples) have shown that high TOC intervals are most prominent in the basal components of prograding clinoforms. By placing the data into a regional seismic and sequence stratigraphic framework we have mapped the lateral extent of TOC-rich zones on the scale of 10s to 100s of kilometers.

The position and lateral extent of the shelf break for key stratigraphic intervals have been identified on sets of 3D seismic data (Dominguez et al., 2017). Using this information, the offset distance between the shelf break and toe of slope (ToS) break can be measured and mapped across the basin. The position of the shelf break, and more importantly, the ToS break, migrates basinward as the time transgressive Quintuco-Vaca Muerta system progrades towards the center of the basin. Strata basinward of the ToS break consists of TOC-rich, condensed section. These intervals have subsequently been overlain producing a map showing the lateral extent of individual or multiple (depending on basin location) intervals with potentially high TOC. This data compilation displays the distribution and both lateral and temporal variability of the organic-rich intervals in the Neuquén Basin.

Furthermore, using a published regional acoustic impedance (AI) line and available subsurface geochemical and petrophysical measurements, we document the thickness of TOC-rich intervals for each stratigraphic interval. The AI data constrain facies types to positions within the geometries of each clinoform and document the lateral and vertical migration of the extent of high TOC strata through each transgressive and regressive hemi-sequences on a seismic scale.

Quantifying the accumulation of organic material over time as the basin progressively fills further refines our depositional concept of the Vaca Muerta-Quintuco system, and aids in our understanding of the evolution preservations of organic matter in the Neuquén Basin.