Changes

Since the initial discovery at the Plaza Huincal Field in 1918, over 14 billion barrels oil equivalent (BBOE) have been discovered in the Neuquén Basin within multiple stacked petroleum systems from the Early Jurassic through the Cretaceous (Figure 2). Over the past 15 years, technological advances from shale development in North America have been deployed to the Vaca Muerta Play, widely recognized as a world-class source rock and now one of the unconventional reservoirs with the highest potential globally. Recent assessments have estimated the undiscovered technically recoverable resource estimates of the Vaca Muerta at between 14.4 and 15.9 BBOE of oil and 38 – 46 trillion cubic feet (TCF) of gas (Schenk et al., 2017; Mayol et al., 2020).

Since the initial discovery at the Plaza Huincal Field in 1918, over 14 billion barrels oil equivalent (BBOE) have been discovered in the Neuquén Basin within multiple stacked petroleum systems from the Early Jurassic through the Cretaceous (Figure 2). Over the past 15 years, technological advances from shale development in North America have been deployed to the Vaca Muerta Play, widely recognized as a world-class source rock and now one of the unconventional reservoirs with the highest potential globally. Recent assessments have estimated the undiscovered technically recoverable resource estimates of the Vaca Muerta at between 14.4 and 15.9 BBOE of oil and 38 – 46 trillion cubic feet (TCF) of gas (Schenk et al., 2017; Mayol et al., 2020).

During deposition of the Vaca Muerta Formation, the Neuquén Basin was a triangular shaped retro-arc basin (Figure 3). The unique configuration of this basin along the western margin of South America was directly related to the confluence of a north – northwest rift system truncated by an east – west system developed between crustal terranes forming the basin basement (Ramos et al., 2020). Combined with variable rates of thermal subsidence throughout the Late Jurassic through Early Cretaceous, the tectonic regimes exerted a first order control on the stratigraphic and sedimentologic variability observed throughout the formation (Dominguez et al., 2020b).

During deposition of the Vaca Muerta Formation, the Neuquén Basin was a triangular shaped retro-arc basin (Figure 3). The unique configuration of this basin along the western margin of South America was directly related to the confluence of a north – northwest rift system truncated by an east – west system developed between crustal terranes forming the basin basement (Ramos et al., 2020). Combined with variable rates of thermal subsidence throughout the Late Jurassic through Early Cretaceous, the tectonic regimes exerted a first order control on the stratigraphic and sedimentologic variability observed throughout the formation<ref name=Dmngz2020b>Domínguez, R. F., O. Catuneanu, H. M. Reijenstein, R. Notta, and H. W. Posamentier, 2020b, [https://archives.datapages.com/data/specpubs/memoir121/data/163_aapg-sp2120163.htm Sequence stratigraphy and the three-dimensional distribution of organic-rich units], ''in'' D. Minisini, M. Fantín, I. L. Noguera, and H. A. Leanza, eds., Integrated geology of unconventionals: The case of the Vaca Muerta play, Argentina: [https://archives.datapages.com/data/alt-browse/aapg-special-volumes/m121.htm AAPG Memoir 121], p. 163–200.</ref>.

Variability in sediment provenance and distribution has been well established via outcrop observations dating to the early 1900s across the basin. Over the past 20 years, seismic imaging and mapping, as well as petrophysical evaluation and log correlation, has focused upon the intervals observed within the Vaca Muerta in an effort to better define and predict the distribution of the high-quality reservoir units (Dominguez et al., 2020b). These efforts have resulted in a detailed stratigraphic framework that accounts for the multiple cycles and directions of clinoform geometries observed across the basin (Figure 4). Petrophysical evaluations have suggested that the highest reservoir quality occurs within the mixed siliceous and calcareous organic-rich facies that occur within proximal bottom sets and basal foresets of the progradational clinoform units (Figure 5; Romero-Sarmiento et al., 2017; Tenaglia et al., 2020; Minisini et al., 2020).

Variability in sediment provenance and distribution has been well established via outcrop observations dating to the early 1900s across the basin. Over the past 20 years, seismic imaging and mapping, as well as petrophysical evaluation and log correlation, has focused upon the intervals observed within the Vaca Muerta in an effort to better define and predict the distribution of the high-quality reservoir units<ref name=Dmngz2020b />. These efforts have resulted in a detailed stratigraphic framework that accounts for the multiple cycles and directions of clinoform geometries observed across the basin (Figure 4). Petrophysical evaluations have suggested that the highest reservoir quality occurs within the mixed siliceous and calcareous organic-rich facies that occur within proximal bottom sets and basal foresets of the progradational clinoform units (Figure 5; Romero-Sarmiento et al., 2017; Tenaglia et al., 2020; Minisini et al., 2020).

Early exploration and development focused almost exclusively upon the organic-rich bottom set intervals described above. Thirty-year EURs from these wells compare favorably with all of the most prolific North American shale plays, with the average 10000 ft lateral well estimated to produce ~ 644,000 BOE combined oil and gas<ref name=Zbrsk /> (Figure 6) proving the Vaca Muerta play as one of the most prolific unconventional resources in the world. However, as acreage across regions containing high-quality bottomset facies was quickly acquired, companies began to evaluate the potential for high quality reservoir units in other parts of the depositional system.

Early exploration and development focused almost exclusively upon the organic-rich bottom set intervals described above. Thirty-year EURs from these wells compare favorably with all of the most prolific North American shale plays, with the average 10000 ft lateral well estimated to produce ~ 644,000 BOE combined oil and gas<ref name=Zbrsk /> (Figure 6) proving the Vaca Muerta play as one of the most prolific unconventional resources in the world. However, as acreage across regions containing high-quality bottomset facies was quickly acquired, companies began to evaluate the potential for high quality reservoir units in other parts of the depositional system.

The stratigraphic and sedimentologic variability of the Vaca Muerta Formation linked to the unique tectonic setting is highly complex and has resulted in significant efforts in re-defining sweet spots outside of the bottomsets mentioned above (Dominguez et al., 2020b; Minisini et al., 2020). Further evaluation of the heterogeneous nature of the lithologies that comprise this formation have demonstrated that high quality reservoirs may exist across multiple lithologies and depositional environments (Figure 5). Recent work by Minisini et al. (2020) evaluating facies variability throughout the Vaca Muerta Play suggested three new play concepts along the foresets of progradational clinoforms (Figure 7) based upon detailed core and thin section descriptions. These play concepts include thin carrier beds within organic-rich units, tight reservoirs within the middle foresets, and stacking of quality reservoirs within specific foresets. Further exploration of these new play concepts is supported by recognition that many of the highest producing wells in the play occur outside of the areas of thickest TOC accumulation (Figure 8). Recognition of these concepts and resultant exploration and development of them may continue to add to the remaining potential of this world-class unconventional reservoir.

The stratigraphic and sedimentologic variability of the Vaca Muerta Formation linked to the unique tectonic setting is highly complex and has resulted in significant efforts in re-defining sweet spots outside of the bottomsets mentioned above<ref name=Dmngz2020b /> (Minisini et al., 2020). Further evaluation of the heterogeneous nature of the lithologies that comprise this formation have demonstrated that high quality reservoirs may exist across multiple lithologies and depositional environments (Figure 5). Recent work by Minisini et al. (2020) evaluating facies variability throughout the Vaca Muerta Play suggested three new play concepts along the foresets of progradational clinoforms (Figure 7) based upon detailed core and thin section descriptions. These play concepts include thin carrier beds within organic-rich units, tight reservoirs within the middle foresets, and stacking of quality reservoirs within specific foresets. Further exploration of these new play concepts is supported by recognition that many of the highest producing wells in the play occur outside of the areas of thickest TOC accumulation (Figure 8). Recognition of these concepts and resultant exploration and development of them may continue to add to the remaining potential of this world-class unconventional reservoir.

==References==

==References==

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Mayol, Juan Cruz, Moridis, Nefeli, McVay, Duane A., and Lee, John W., 2020. Assessment of Oil and Gas Resources in the Vaca Muerta Shale, NeuquénBasin, Argentina. Paper SPE 199035 presented at the SPE Symposium on Latin American and Caribbean Petroleum Engineering Conference, virtual, July 27 - 31, 2020.  

Mayol, Juan Cruz, Moridis, Nefeli, McVay, Duane A., and Lee, John W., 2020. Assessment of Oil and Gas Resources in the Vaca Muerta Shale, NeuquénBasin, Argentina. Paper SPE 199035 presented at the SPE Symposium on Latin American and Caribbean Petroleum Engineering Conference, virtual, July 27 - 31, 2020.