Changes

The history of the discovery and development of the Vaca Muerta play dances for more than a decade with an intense series of events, such as the international search of new unconventional resources, the nationalization of the main operator, dramatic shifts in fiscal regime, a quick evolution of the play concepts (from vertical to horizontal wells) and of technology (from 500 to 3000 m laterals), and the Covid-19 pandemic. Nevertheless, the situation allowed conditions for economic success.

The history of the discovery and development of the Vaca Muerta play dances for more than a decade with an intense series of events, such as the international search of new unconventional resources, the nationalization of the main operator, dramatic shifts in fiscal regime, a quick evolution of the play concepts (from vertical to horizontal wells) and of technology (from 500 to 3000 m laterals), and the Covid-19 pandemic. Nevertheless, the situation allowed conditions for economic success.

The geological knowledge of the Vaca Muerta play derives from (1) data gathered during the last decade, related to the search and discovery of the Giant Field Vaca Muerta, and (2) the legacy of 100 years of activity of the O&G industry in the Neuquén Super Basin. The integration of the geological disciplines, at different scales, presents a unique unconventional play, exceptionally thick (100–400 m), vast (30,000 km2), and porous (10%–20%), with a prograding clinoform hosting up to eight landing zones, and all types of fluid segments (from black oil to dry gas).

The geological knowledge of the Vaca Muerta play derives from (1) data gathered during the last decade, related to the search and discovery of the Giant Field Vaca Muerta, and (2) the legacy of 100 years of activity of the O&G industry in the Neuquén Super Basin. The integration of the geological disciplines, at different scales, presents a unique unconventional play, exceptionally thick (100–400 m), vast (30,000 km²), and porous (10%–20%), with a prograding clinoform hosting up to eight landing zones, and all types of fluid segments (from black oil to dry gas).

The current play concept consists in landing the horizontal wells in the proximal bottomsets and lower foresets of the clinoform, sectors with higher hydrocarbon potential and easier fracture growth. The rocks in these sectors show the best reservoir characteristics (averages: TOC 5%; porosity 12%; clay 10%–20%; water saturation 20%), the most adequate geomechanical properties (homogeneous rock with Young’s Modulus <4 Mpsi, low Poisson Ratio ~0.25, and interfaces with weak geomechanical contrasts), and a thick vertical stack (30–40 m) of lithofacies with the aforementioned characteristics. With this concept in mind, at least two landing zones have been fully de-risked, and other six have been confirmed.

The current play concept consists in landing the horizontal wells in the proximal bottomsets and lower foresets of the clinoform, sectors with higher hydrocarbon potential and easier fracture growth. The rocks in these sectors show the best reservoir characteristics (averages: TOC 5%; porosity 12%; clay 10%–20%; water saturation 20%), the most adequate geomechanical properties (homogeneous rock with Young’s Modulus <4 Mpsi, low Poisson Ratio ~0.25, and interfaces with weak geomechanical contrasts), and a thick vertical stack (30–40 m) of lithofacies with the aforementioned characteristics. With this concept in mind, at least two landing zones have been fully de-risked, and other six have been confirmed.

===Stratigraphic Setting===

===Stratigraphic Setting===

The Vaca Muerta Formation corresponds to the distal facies of a clinoform system developed during a shallowing-upward sedimentary cycle, lasting approximately 11 My, known as the Vaca Muerta–Quintuco system<ref>Mitchum, R. M., and M. A. Uliana, 1982, Estratigrafía sísmica de las formaciones Loma Montosa, Quintuco y Vaca Muerta, Jurásico Superior y Cretácico Inferior de la Cuenca Neuquina, República Argentina: 1° Congreso Nacional de Hidrocarburos, Petróleo y Gas: Buenos Aires, Argentina, Actas, p. 439–484.</ref><ref> Spalletti, L., and G. Veiga, 2007, Variability of continental depositional systems during lowstand sedimentation: An example from the Kimmeridgian of the Neuquén Basin, Argentina: Latin American Journal of Sedimentology and Basin Analysis, v. 14, p. 85–104.</ref>. The Vaca Muerta is associated with the bottomsets and foresets of the clinoforms, consisting of organic-rich mudstones and marlstones. The Quintuco Formation represents the topsets, and consist of grainstones, wackestones, and dolostones. The progradation of the clinoforms created a thickening of the Vaca Muerta toward the northwest. It is in this vertical stack of organic-rich units where industry is landing the unconventional horizontal wells (e.g., Vittore et al.<ref name=Vttor2020 />; [[:file:M125-VacaMuerta-Figure5.jpeg|Figure 5]]).

The Vaca Muerta Formation corresponds to the distal facies of a clinoform system developed during a shallowing-upward sedimentary cycle, lasting approximately 11 My, known as the Vaca Muerta–Quintuco system<ref>Mitchum, R. M., and M. A. Uliana, 1982, Estratigrafía sísmica de las formaciones Loma Montosa, Quintuco y Vaca Muerta, Jurásico Superior y Cretácico Inferior de la Cuenca Neuquina, República Argentina: 1° Congreso Nacional de Hidrocarburos, Petróleo y Gas: Buenos Aires, Argentina, Actas, p. 439–484.</ref><ref> Spalletti, L., and G. Veiga, 2007, Variability of continental depositional systems during lowstand sedimentation: An example from the Kimmeridgian of the Neuquén Basin, Argentina: Latin American Journal of Sedimentology and Basin Analysis, v. 14, p. 85–104.</ref>. The Vaca Muerta is associated with the bottomsets and foresets of the clinoforms, consisting of organic-rich [[mudstones]] and marlstones. The Quintuco Formation represents the topsets, and consist of grainstones, wackestones, and dolostones. The progradation of the clinoforms created a thickening of the Vaca Muerta toward the northwest. It is in this vertical stack of organic-rich units where industry is landing the unconventional horizontal wells (e.g., Vittore et al.<ref name=Vttor2020 />; [[:file:M125-VacaMuerta-Figure5.jpeg|Figure 5]]).

The prograding clinoforms are here subdivided into six units<ref name=Mnsni2020a /> ([[:file:M125-VacaMuerta-Figure5.jpeg|Figure 5]]). Each unit represents a transgressive-regressive sedimentary cycle of third order. The sedimentary cycles show that the highest total organic carbon (TOC) is recorded during the late transgressive systems tract (TST) and early highstand systems tract (HST), when organic matter accumulated both in the bottomset and along the foresets, forming condensed sections. During the falling stage systems tract (FSST), sediment bypassed the topsets increasing the sediment accumulation rate in the foresets, which resulted thicker and diluted in TOC. During the lowstand systems tract (LST), organic-rich intervals accumulated only in the distal bottomsets ([[:file:M125-VacaMuerta-Figure5.jpeg|Figure 5]]). The maximum thickness of the organic-rich intervals results parallel to (and basinward of) the shelf break, and the maximum area covered by the organic-rich intervals is associated with the least steep foresets<ref name=Dmngz2020 />. These observations suggest that the organic matter distribution is controlled by the construction of the clinoform and may be predicted through the sequence stratigraphy ([[:file:M125-VacaMuerta-Figure9.jpeg|Figure 9]]). Because thick units with high TOC (and associated high porosity) are fundamental elements for a landing zone, the proximal bottomsets and the lower foresets were soon indicated as zones with high hydrocarbon prospectivity ([[:file:M125-VacaMuerta-Figure5.jpeg|Figure 5]]).

The prograding clinoforms are here subdivided into six units<ref name=Mnsni2020a /> ([[:file:M125-VacaMuerta-Figure5.jpeg|Figure 5]]). Each unit represents a transgressive-regressive sedimentary cycle of third order. The sedimentary cycles show that the highest total organic carbon (TOC) is recorded during the late transgressive systems tract (TST) and early highstand systems tract (HST), when organic matter accumulated both in the bottomset and along the foresets, forming condensed sections. During the falling stage systems tract (FSST), sediment bypassed the topsets increasing the sediment accumulation rate in the foresets, which resulted thicker and diluted in TOC. During the lowstand systems tract (LST), organic-rich intervals accumulated only in the distal bottomsets ([[:file:M125-VacaMuerta-Figure5.jpeg|Figure 5]]). The maximum thickness of the organic-rich intervals results parallel to (and basinward of) the shelf break, and the maximum area covered by the organic-rich intervals is associated with the least steep foresets<ref name=Dmngz2020 />. These observations suggest that the organic matter distribution is controlled by the construction of the clinoform and may be predicted through the sequence stratigraphy ([[:file:M125-VacaMuerta-Figure9.jpeg|Figure 9]]). Because thick units with high TOC (and associated high porosity) are fundamental elements for a landing zone, the proximal bottomsets and the lower foresets were soon indicated as zones with high hydrocarbon prospectivity ([[:file:M125-VacaMuerta-Figure5.jpeg|Figure 5]]).