ABSTRACT The present-day structure of the Neuquén Basin is the result of the deformation of the sedimentary column through a poly-episodic tectonic history. The initial stage was dominated by extension with a general northeast–southwest direction during the Early Jurassic. The resultant structures were a widespread distribution of northwest–southeast striking grabens and half-grabens defined as the Rift stage. Subsequently, different stages of convergent tectonics took place with different directions of convergence vectors, reactivating and inverting the previous extensional structures and creating new ones. The most important stages were the Aluk stage (Early Jurassic-Early Cretaceous), the Farallon stage (Cretaceous), and the Nazca stage (Cenozoic). The tectonic pulses produced distinctive megastructures that affected the early Tithonian to early Valanginian Vaca Muerta Formation, such as the Chihuidos High, the Huincul High, and the Agrio fold-and-thrust belt. Also, multiple fault systems forming kilometer-scale features were created. The main fault systems affecting the Vaca Muerta–Quintuco system are classified according to the Anderson classification: normal, reverse, and strike-slip faults. The following fault families are identified: five normal fault families (northwest–southeast, east-northeast–west-southwest, north-northeast–south-southwest, north-south, and radial), five reverse (high-angle) fault families (east–west, northeast–southwest, north–south, north-northeast–south-southwest, and circular), two thrust (low-angle) fault families (north-northwest–south-southeast and north-northeast–south-southwest), and one strike-slip fault family (east-northeast–west-southwest). The geometrical characteristics, orientations, and distribution of these Vaca Muerta fault families are presented and the interpretation of their genesis is discussed. Second-order structures such as volcanic dikes and sills, soft-sediment deformations and accomodation/transfer zones that participate to the deformation of the Vaca Muerta-Quintuco system are also described because they also affect the unconventional self-sourced play. Finally, some structural aspects of the Chihuidos High, the impact of the inheritance on the Vaca Muerta–Quintuco structures (geometry, orientation, and distribution) and the Structural Risk Analysis are discussed.

The Neuquén Embayment, which developed along the eastern foothills of the southern Central Andes, has a complex history of intraplate deformation. The Paleozoic basement fabrics exerted a major influence in Mesozoic and Cenozoic deformation. The most important feature is an E-W–striking fault system that is related to a late Paleozoic fabric and is associated with the Huincul basement high, which truncates the basin. This fabric is interpreted as being the result of the accretion of the Patagonia terrane with Gondwana during the Early Permian. Two-dimensional (2D) and three-dimensional (3D) seismic coverage and subsurface information identify different sectors in the Neuquén Embayment that record alternating episodes of contraction and extension during the Jurassic and Cretaceous. The deformation history east of the thrust front of the Agrio fold-and-thrust belt is characterized by periods of (1) transpression and almost orthogonal contraction to the continental margin, (2) extension, and (3) relative quiescence, which alternates in different sectors. The earliest shortening occurred in the Early Jurassic when the main stress was oriented in the N-NW sector. The stress rotated to the northwest up to Valanginian times, when a more orthogonal orientation to the continental margin became dominant and prevailed after the Cenomanian. After a period of quiescence in the Neuquén Embayment associated with very oblique subduction during the Paleogene, the final contractional deformation took place in the late Miocene, with a west-east orientation of the main stress, and was followed by Pliocene extension. The changing stress patterns correlate with differences in convergence vectors between the Aluk, Farallon, and Nazca oceanic plates and the Gondwana or South American continental plates. The Aluk stage from the Jurassic to the Valanginian was characterized by tectonic inversion that is shown by shortening and right-lateral strike-slip structures that are concentrated in the Huincul system and more subtle deformation in the Chihuidos and Entre Lomas systems. The early Farallon stage was distinguished by reduced inversion and displacement in the Huincul system and a general retreat of deformation after the Valanginian. The change to late Farallon stage was characterized by a prominent tectonic inversion of the Entre Lomas system, which resulted from the inception of the formation of the Agrio fold-and-thrust belt in the retroarc area. This belt developed during most of the Late Cretaceous, when the embayment showed a general quiescence. The Nazca stage was characterized by the main episode of uplift, tectonic inversion of the older half-grabens, and important strike-slip faulting that was followed by local collapse of some structures during the Pliocene.

ABSTRACT The Vaca Muerta Formation (Late Jurassic–Early Cretaceous) bears a high-quality, oil-prone kerogen deposited under mostly anoxic, marine conditions and constitutes a world-class source rock with outstanding geochemical characteristics for the generation of petroleum (oil and gas) throughout the Neuquén Basin. The formation has been identified as the main source for the majority of the hydrocarbon pools found in conventional reservoirs of the basin, but in the last ten years, it has also acquired significance as a self-sourced unconventional reservoir target for both oil and gas. An extended database that comprises several tens of thousands of samples, including cuttings, cores, sidewall cores, and outcrops of the Vaca Muerta Formation from wells and outcrop sections along the entire basin was evaluated. This allowed formulating patterns of organic richness, hydrocarbon source quality, and distribution of free hydrocarbons in six reference areas of the basin. These reference areas are defined based either on the impact of the sedimentary rock on generated hydrocarbons or on the significant thermal maturity differences. The areas are: Malargüe, Chihuido-Lomita, Northeast Platform, Embayment, Huincul Arch, and Picún Leufú. More than 300 oils and organic extracts from Vaca Muerta and nearly 500 mud and production gas samples completed the data set to understand the key features of the fluids occurring in the prospectable areas for unconventional resources (shale oil and shale gas). Collected and evaluated analytical data include total organic carbon (TOC), programmed pyrolysis, visual kerogen analyses, bulk chemical composition of fluids, gas chromatography (GC) and gas chromatography–mass spectrometry for biomarker fingerprints (GCMS), stable carbon isotopes, bulk and compositional kinetics, and x-ray fluorescence (XRF). Moreover, insights into the essential processes of the Vaca Muerta unconventional petroleum system including kerogen-related issues and basin-scale processes are discussed in terms of source rock kinetics, modeling of burial/exhumation histories, porosity development, and overpressure occurrence. The Embayment area stands out as the most attractive for unconventional development to produce middle-to-light oil with low sulfur content along with gas condensate westward. An analogous pattern is observed in the Chihuido-Lomita and Huincul Arch areas, with similar source rock characteristics but with overall lower thermal maturity compared with the Embayment area. However, in the transition to the Northeast Platform, the northeastern fringe of Chihuido-Lomita and Embayment areas present middle-to-heavy, mostly sulfur-rich oils, with limited gas potential, hence requiring higher permeability to yield commercial production. The Malargüe area is characterized by overall mid maturity and limited quality of oil (middle to heavy), predominantly sulfur-rich. Finally, the Picún Leufú area is conditioned by a source rock with low potential because of thinner organic-rich intervals and low-to-middle thermal maturity.

ABSTRACT The present-day “Andean” configuration of the Neuquén Basin has been classically used in most paleogeographic reconstructions of the existing literature as a consequence of the compressive deformation episode of the Andean orogeny, which resulted in a foreland stage initiated during the Late Cretaceous. The configuration displays its classic structural elements and morphostructural domains, as well as the origin of fold-and-thrust belts. Conversely, based on a great amount of preexisting data, it has been noticed that the present-day “Andean” configuration greatly differs from that of the basin during the deposition of the Vaca Muerta Formation, when a stage of subduction-related thermal sag with some punctuated episodic inversions took place, in a retro-arc basin context. This chapter analyzes the paleoconfiguration of the basin during the time in which the Vaca Muerta-Quintuco system was deposited (early Tithonian to early Valanginian). The basin paleoconfiguration during that interval clearly represents a first-order geological control on the stratigraphic architecture of the Vaca Muerta Formation (clinoform internal and external geometries, progradation patterns, extent), as well as on the mineralogical composition and thicknesses of the organic-rich facies.

The southern Central Andes of Argentina between 35° and 39°S latitude can be divided into two sectors with contrasting geological histories. The boundary between the sectors coincides with the Cortaderas lineament. North of the Cortaderas lineament, the Andes record a foreland expansion of arc magmatism that is associated with contractional deformation in the Malargüe fold-and-thrust belt, and subsidence of the Río Grande foreland basin between 15 and 5 Ma. The peak expansion of deformation into the foreland occurred as late Miocene magmatic arc rocks erupted more than 500 km east of the trench and the San Rafael basement block was uplifted in central Mendoza. This stage was followed by the collapse of the basement uplift by normal faulting, the retreat of the magmatic arc, and the eruption of widespread late Pliocene to early Pleistocene within-plate lava flows in the Payenia region. Extensive Quaternary calderas and rhyolitic domes along the axis of the main Andes reflect crustal melting associated with basaltic underplating. In contrast, the structural evolution of the sector south of the Cortaderas lineament is dominated by the Late Cretaceous development of the Agrio fold-and-thrust belt, which underwent minor reactivations in the Eocene and the late Miocene. The post-Miocene Guañacos fold-and-thrust belt that has since developed along the axis of the main Andes concentrates neotectonic contraction. Arc magmatism in this sector is largely restricted to the axial area of the Andes. Both the sectors north and south of the Cortaderas lineament show evidence of an important episode of extension during the Oligocene to early Miocene, and for renewed extension in the Pliocene and the Pleistocene. The contrasting geological histories north and south of the Cortaderas lineament reflect differences in the geometry of the subducting plate, variations in crustal rheologies inherited from a more restricted distribution of Mesozoic rifts in the northern than the southern segment, and variations in the trench roll-back velocity through time.

ABSTRACT The Vaca Muerta Formation consist of outer ramp to basinal facies in a mixed siliciclastic–carbonate creating an organic-rich section up to 500 m thick. This chapter documents stratal terminations, main bounding surfaces, and stacking patterns of the Vaca Muerta–Quintuco system as a means to establish a new sequence stratigraphic framework. The data set comprises more than 500 wells and a basin-scale seismic coverage that spans 30,000 km 2 Regional seismic interpretations and well correlations were calibrated with well geochemical data and acoustic impedance seismic sections. Twelve high-frequency depositional sequences (HFS) with variable combinations of systems tracts were defined and grouped in three low-frequency depositional sequences (LFS). Within this sequence stratigraphic framework, the Vaca Muerta Formation includes organic-rich (total organic carbon, TOC > 2wt. %) and organic-poor intervals (TOC < 2wt. %) At a high-frequency scale, the organic-rich intervals with the highest concentration of TOC belong to transgressive systems tracts and the lower sections within clinoform bottomset and foreset of highstand systems tracts. These condensed sections usually show the best reservoir properties in the self-sourced unconventional play. Conversely, organic-poor intervals are found in the foresets of falling-stage systems tracts and lowstand systems tracts. Condensed sections of each sequence allow subdivide the unconventional play in a stacking of 12 organic-rich Vaca Muerta units (OVM, TOC ≥ 2wt. %). The lowermost eight OVM units correspond to the main tested landing zones. Moreover, a detailed map of shelf breaks reveals a strong three-dimensional (3-D) spatial variability, which is summarized in four groups of plan-view geometries. The 3-D spatial variability of the organic-rich intervals is analyzed at local scale in two cases with different plan-view geometries. At regional scale, thickness maps of the main OVM units allow infer stratigraphic controls (e.g., systems tracts, previous clinoform paleo-topography) and tectonic controls, both regional (morphostructural domains) and local (subsidence axes and paleo-highs), active during the deposition of the Vaca Muerta Formation. The proposed sequence stratigraphic framework provides a predictive understanding of 3-D spatial distribution of the organic-rich intervals in subsurface assessments for the Vaca Muerta play and is applicable to the exploration of other analogous (mixed siliciclastic-carbonate systems) self-sourced unconventional resources.