Vaca Muerta Research Articles

The Huncal Member of the Vaca Muerta Formation, Neuquén Basin of Argentina: Insight into biostratigraphy, structure, U-Pb detrital zircon ages and provenance

In the western sector of the Neuquén Basin, the organic-rich shales of the Vaca Muerta Formation are intercalated with turbidite sandstone intervals and slump structures integrated in the Huncal Member. The age of the Huncal sandstones based on the integration of the ammonite faunas, calcareous nannofossils and U-Pb analysis is late Berriasian in their type locality. The origin of this deposit is probably related with two lobes of turbiditic sandstones linked with a progradational regressive phase. Sandstones are lithic arkoses and feldspathic litharenites derived from recycled orogenic and dissected arc sources. The U-Pb ages confirm a mixed sedimentary provenance from the south and southeastern margins of the basin, specifically from Paleozoic and Triassic–Jurassic rocks of the North Patagonian Massif and the Huincul High. The complex fold and fault system described in the sandstone levels was interpreted as the result of slump processes with a main transport direction to the SW and W. Sandstone deposits with slump structures assignable to the Huncal Member are present throughout the entire basin from the Tithonian to the Valanginian in the Vaca Muerta Formation. Therefore, the Huncal Member is a diachronic lithostratigraphic unit and its deposition probably depended on different factors such as relative sea level changes, the position in the ramp system or in the platform and slope configuration and internal morphostructural features of the Neuquén Basin.

Geochemistry of shale gases from around the world: Composition, origins, isotope reversals and rollovers, and implications for the exploration of shale plays

We studied a large dataset of ∼2600 shale gas samples from 76 geological formations in 38 sedimentary basins located in eleven countries. Shale gases contain mostly hydrocarbons dominated by methane. Shale gases can have primary microbial, secondary microbial and thermogenic origin. However, gases produced from most commercially successful shale plays (e.g., the Marcellus, Haynesville, Eagle Ford and Barnett in the USA, the Vaca Muerta in Argentina and the Wufeng-Longmaxi in China) are thermogenic. It appears that formations with greater gas endowment such as the Marcellus and the Haynesville contain late-mature thermogenic gas. Shale plays with early-mature thermogenic and secondary microbial gas such as the Antrim (USA) and the New Albany (USA) formations have relatively low endowments of recoverable gas. Shale plays with primary microbial gas are not significant from commercial exploration perspective. Isotope reversals (δ13C of methane > δ13C of ethane) are observed in shale plays with mature organic matter (vitrinite reflectance > 2%) that experienced significant uplift (>2 km). It appears that isotope fractionation during desorption from depressurized late-mature shales leads to isotope reversal in the residual gas produced from shale formations (e.g., the Wufeng-Longmaxi). Significant contribution of adsorbed gas (enriched in 13C-rich C2+ hydrocarbons relative to the co-occurring free gas) in the production from some plays (e.g., the Fayetteville, USA) may result in isotope rollovers.

Analytical orientation criteria for drilling and completion-induced fracture initiation considering fluid infiltration from the wellbore

Analytically-developed criteria are presented for the orientation of fracture initiation in porous-permeable rocks considering fluid infiltration from non-perforated and perforated wellbores. For non-perforated wellbores, this is a fully-exact analytical solution representing the initiation of drilling-induced tensile fractures (DITFs). For perforated wells, a set of analytical approximations are derived for fracture initiation representing completion-induced hydraulic fractures (CIHFs). DITF orientation is used to constrain the in-situ stress tensor, especially in the case of transverse DITFs, which are rarer than longitudinal DITFs. Results indicate that transverse CIHF initiation only occurs over a wellbore pressure-at-breakdown window, while longitudinal CIHF initiation occurs at comparatively higher wellbore pressures. Transverse CIHF initiation however, occurs more frequently than transverse DITFs, because the presence of perforations aids transverse fracture initiation. Low Biot's poroelastic coefficient and high Poisson's ratio values also aid transverse fracture initiation. The region of the in-situ stress states where transverse initiation is promoted can be shown in dimensionless plots. Case studies are run on seven prolific shale plays (Barnett, Bakken, Fayetteville, Haynesville, Niobrara, Marcellus, and Vaca Muerta) using breakdown pressures from the literature. Transverse CIHF initiation is found to be a highly likely outcome, as opposed to results from past studies that neglected pore pressure effects. Based on the findings of this study, recommendations are made to practitioners to enhance their chances on achieving transverse CIHF initiation in the field. These involve slow injection rates, oriented perforation strategy and strong bonding between the casing, cement and the surrounding rock to prevent fracturing fluid leakages.

A methodology for unstructured damped stress inversion of microseismic focal mechanisms: Application to the Vaca Muerta Formation, Argentina

Current methodologies for stress inversion from microseismic focal mechanisms require the assignment of events to a regular grid and then solving for the stress state at each grid node. This approach can lead to irregularities in the solution because some nodes may contain few or even no events. To address this issue, we modified the algorithm to solve for stresses on an irregular (unstructured) grid. We first use the [Formula: see text]-means algorithm to split the data into suitably sized groups. The centroids of these groups are then considered as the nodes of an unstructured grid, and we simultaneously solve for the stress state in each group using damped inversion. To account for the irregularity of the unstructured grid, we use the reciprocal square distance between nodes as weights, as opposed to the existing method in which a weight of unity is assigned between adjacent nodes on a regular grid. Focal planes are selected from the auxiliary plane using the fault instability criterion. The method is first applied to synthetic data sets in which we simulate and subsequently invert for the stress field around a mode-I fracture at depth, in a strike-slip and in a normal faulting stress regime. Results indicate a stress orientation error of 10° and a stress ratio error between 1% and 10%. We then consider focal mechanism data from an unconventional shale play in the Vaca Muerta Formation in Argentina, and our results suggest the presence of a preexisting strike-slip faulting stress regime. We also find that the unambiguous focal plane picks suggest that the apparent dip-slip focal mechanisms are indeed dip-slip movement along subvertical natural fractures, which correlate well with image log data. We suggest that these dip-slip events are caused by stress changes induced by the opening of the hydraulic fractures.

Geomechanical properties of the Vaca Muerta Formation

Unconventional oil and gas resources have transformed the energy industry in the United States. Likewise, other countries have followed up with hydrocarbon exploitation from tight unconventional formations. One of the most developed unconventional fields outside North America is the Vaca Muerta Formation in the Neuquén Basin, Argentina. This study summarizes experimental results of quasi-static loading and elastic wave propagation in rocks from the Vaca Muerta Formation along the entire producing interval. The work summarizes experimental results from our laboratory and from the literature. The results highlight the variability of mechanical properties with mineralogy and composition, and the mechanical anisotropy induced by layering. The discussion section explores the implications of spatial variability and anisotropy on in-situ stresses and fluid-driven fractures. Accurate characterization of rock mechanical properties is critical for predicting the geometry of fluid-driven fractures in unconventional rock formations, particularly those subjected to a tectonically active environment such as the Vaca Muerta Formation.

An Unconventional Challenge Can Casing Failures During Hydraulic Fracturing Be Stopped?

Shale producers around the world have learned in recent years that they cannot take wellbore integrity for granted. During pressure-pumping treatments, the interplay of hydraulic fracturing and formation geomechanics is deforming and even shearing steel casing. In the worst of cases, this means that some operators have lost access to long sections of a wellbore before it produces a single barrel of oil. This is largely not viewed as an inter-well challenge similar to frac hits. Rather, it is considered to be intrawell phenomena. The problem can take several forms and has no universal driver. George King, an independent consultant and leading technical voice on hydraulic fracturing, points out that not every unconventional asset is affected—indicating that geology and understanding of the rock fabric matter. However, information he has collected from client operators shows that in certain US shale and tight oil fields, between 20%–30% of horizontal wells are impacted to some degree. “Sometimes it is with the cement support, and sometimes it is with the casing itself,” said King, listing two of the problem’s general root causes. He added that the casing deformation is “an artifact of some damage that we are seeing right now in the realm of fracturing, and [during] the time period of fracturing.” A commonly reported version of the problem emerges after just a few stages at the toe-end of a horizontal well have been fractured. As another plug is pumped downhole to continue the completion, it suddenly stops 1,000 ft to 5,000 ft short of its target. This could happen in the bend, or it could be somewhere deep in the lateral. Often the deformation is described as ovalling. If a restriction consumes much more than a tenth of an inch of the pipe’s original internal diameter, there is the potential that unstimulated stages beyond the stopping point are lost to conventional plug-and-perf methods. This fate can sometimes be avoided by running slim-profile perforating guns, but then other isolation technologies are still needed to replace conventional plugs. Unconventional operators in China, Argentina, Canada, and the US have all faced the issue. In response, the technical community has recently stepped up collaboration efforts at industry conferences to find answers. In China, the issue appears to be more widespread on a per-well basis. National oil companies working the Sichuan Basin, the country’s most active unconventional area, have reported that more than 40% of gas wells have experienced casing deformation or failures. Like their US counterparts, Chinese operators typically realize the problem during a post-fracturing tool run. Argentina’s Vaca Muerta is not immune either. A 2015 technical paper coauthored by researchers at Chevron and YPF (URTeC 178620) casts casing shear and restrictions as common and “extremely detrimental to the performance of the well.” When explaining why the issue is cropping up today, more than a decade into the shale revolution, experts are quick to point out that a lot has changed since the first horizontally drilled and hydraulically fractured wells.

Taxonomic revision and palaeobiogeographic affinities of Berriasian–Valanginian oysters from the Vaca Muerta and Mulichinco formations, southern Mendoza, Neuquén Basin, Argentina

Oysters are very abundant in marine Jurassic–Cretaceous deposits across the world, which has led to multiple taxonomic studies since the nineteenth century. In contrast, South American Jurassic–Cretaceous oysters have been largely neglected in the literature. Here, focus is on Berriasian–Valanginian oysters from previously undocumented benthic faunas of southern Mendoza (Neuquén Basin, Argentina). Four species belonging to three genera of the Family Gryphaeidae, Subfamily Exogirinae are described, including their shell microstructure characterization, and their taxonomic status is discussed. Of the studied genera, Aetostreon and Ceratostreon have been widely recorded in the Neuquén Basin previously, whereas the genus Nanogyra is recorded for the first time in Argentina. Aetostreon is represented by A. subsinuatum and A. latissimum, and Ceratostreon and Nanogyra by C. hilli and N. (N.) brevisulcata n. sp. The oldest worldwide records of A. subsinuatum (Berriasian) and C. hilli (Valanginian) are documented here. The paleobiogeographic distribution of these species suggests a Tethyan distribution for A. subsinuatum and A. latissimum and a Trans-Temperate-Pacific distribution for C. hilli, while N. (N.) brevisulcata is endemic to the basin. The three genera appear as isolated records and different types of oyster mass occurrences (OMOs), classified according to its lateral extension, geometry, maximum thickness, and stratigraphic relevance. The different hierarchy of the OMOs could possibly represent different scales of palaeoenvironmental and/or stratigraphic changes, from basin-wide to local level, and could provide tools to identify variations in palaeoenvironmental parameters such as sedimentation rate, siliciclastic and nutrient input and salinity variations.

La Vaca Muerta no dejó ver el bosque: tres tendencias del desarrollo del fracking en Argentina en el periodo 2012-2019

El artículo aborda los primeros años de explotación de la formación Vaca Muerta (2012-2019) en la Patagonia Argentina, tomándola como un caso testigo. Su objetivo es tanto caracterizar el modelo hidrocarburífero no convencional, como describir las principales tendencias que posibilitaron su desarrollo. Para ello se busca, en primer lugar, situar a este tipo de explotación en el marco de la explotación de energías extremas durante la fase neoliberal en todo el continente. Posteriormente revisa los principales ejes identificados a lo largo de este proceso como son: la creación de un discurso oficial que permitió el desarrollo del fracking en un escenario altamente conflictivo; el alto impacto social y ambiental de su desarrollo, y la promoción directa por parte del Estado a través de cuerpos legales y millonarias transferencias. Dicho análisis se hace a través de la revisión de prensa, políticas públicas y medios especializados que permiten sistematizar este proceso desde la perspectiva de la ecología política.

Shale Producers Adopt Geochemistry Fingerprinting to Quantify Cross-Well Production

Obtain a sample of reservoir rock, heat it up, add pressure, and then take a real close look at the drop of oil that comes out to find its unique “fingerprint.” At a high level, this is the emerging extraction and geochemistry process that more than two dozen tight-oil producers have recently adopted to solve one of the shale sector’s biggest mysteries: how does oil flow through the rock matrix and into a hydraulically fractured horizontal well? In a stacked formation, that question branches off into a few more: how much do neighboring horizontal wells communicate, which zones are co-producing the most, and how do these factors change over time? “The ground truth comes when you collect rock, and know exactly what depth that rock comes from, and then extract hydrocarbons from that rock to know the fingerprint of that depth,” said Faye Liu, the founder and chief executive of geochemistry startup RevoChem. Founded last year, the Houston-based firm has so far identified a geochemical fingerprint in more than 5,000 reservoir rocks and produced oil samples from more than 300 wells in nine different shale plays in North America and the Vaca Muerta Shale in Argentina. Every new sample sheds a bit more light on the complex flow patterns of unconventional reservoirs. Among RevoChem’s findings is that pad wells placed in different benches of a tight reservoir stand a high chance of experiencing some level of cross-well communication (Fig. 1). “All of your oil is a mixture coming from multiple zones,” explained Liu who was formerly a geochemist with Conoco Phillips. She noted that despite how they appear in modeling software, the evidence from geochemical fingerprinting shows that hydraulic fractures often extend out of their target zone and into other oil-rich layers of rock. “Essentially, every operator is experiencing the same•process.” A primary goal for adopters of the technology is to describe that vertical drainage in detail—and how the profile changes over time. “In a stacked development, every subsurface professional must be engaged with that understanding,” said Toby Deen, a senior engineer with private Permian oil and gas company Felix Energy, which started conducting time-lapse fingerprinting earlier this year. In addition to vertical production allocation, operators are using geochemical fingerprinting to overcome the difficulty that other diagnostics have had in assessing the related parameter of fracture height. If wells are believed to have a fracture height somewhere in the range of 400–600 ft, then using wider distances between vertically separated wells to avoid interference is justified. However, if the geochemistry shows that only 5–10% of the cross-well production is from the extreme tips of such a fracture network, then wider spacing may not be optimal (Fig. 2). What would make future spacing decisions easier is if an operator could prove that a majority of production is coming from an area just 200–300 ft away from the wellbore. “That means there is a lot of infill potential,” said Liu.

Estimating rock physical parameters using anisotropic 3D seismic data to characterize unconventional Vaca Muerta oil shale deposits in the Neuquèn Basin, western Argentina

Summary Acquisition and processing of wide azimuth large offset and high fold (WA/LO/HF) 3D seismic data in the Aguada Federal concession is presented. Preserved amplitude/azimuthal workflows (e.g. anisotropy analysis, pre-stack elastic inversion, reservoir characterization) facilitate the quantitative interpretation. Layering, fracture distribution and stress cause measurable velocity anisotropy. Well ties and residual normal move-out help to determine the anisotropy parameters (η, e and δ). Non-hyperbolic 4th-order move-out improves flattening of gather reflections. Sinusoidal residual move-out on common-offset, common-azimuth gathers is diagnostic for HTI anisotropy. Azimuthal Residual Move-out (ARMO) on gathers improves the seismic quality. Anisotropic 3D tomographic raytracing and velocity model building increase the depth imaging efficiency. The new processing better focuses the seismic reflections and boosts higher frequencies. The migration repositions the energy in depth and the mismatch of geologic markers at the well locations is reduced. Higher fidelity datasets are better suited for seismic inversion, reservoir characterization and fracture prediction. The anisotropic workflow serves to estimate Vp, Vs, density, total organic contents, Young’s modulus E and pore pressure. Delineation of Vaca Muerta sweet spots is thus made possible. Seismic anisotropy analysis allows optimization of the well landing point, selection of well spacing and a preferred trajectory orientation.

Periplatform ooze in a mixed siliciclastic-carbonate system - Vaca Muerta Formation, Argentina

Thick carbonate mud successions and marl/limestone alternations are often found in periplatform environments. The sources of these fine-grained sediments and the processes that govern their accumulation and distribution in the basin are frequently a matter of debate. This case study from a mixed siliciclastic-carbonate succession in the Neuquén Basin, Argentina, relates the origin of the carbonate-dominated intervals to shelfal carbonate production. The Tithonian-early Valanginian basinal strata (Vaca Muerta Formation) contains several carbonate-rich intervals at different stratigraphic levels. The thickest of these intervals is the mid-late Tithonian Los Catutos Member in Sierra de la Vaca Muerta. This wedge-shaped package of micritic limestones and intercalated marls thins basinwards. Proximal-distal variations and cyclic partitioning in facies and geochemical proxies indicate highstand shedding and a periplatform origin for the Los Catutos Member. The proposed source is a coeval 20 m-thick pure carbonate interval located 50 km south of the Sierra de la Vaca Muerta within the mixed siliciclastic-carbonate shelf facies of the Picún Leufַú Formation. Younger carbonate-rich intervals in the center of the basin (Puerta Curaco area) show similar characteristics to the distal portion of the Los Catutos Member and are also interpreted as periplatform deposits but sourced from carbonate shelves farther east. The high sedimentation rates of the Los Catutos Member require an efficient mechanism, other than tides and winds, to deliver significant amounts of fine-grained carbonate sediment to the basin. This mechanism is envisioned to be sediment-charged hyperpycnal flows cascading from the platform to the basin, analogous to what is observed in modern carbonate systems. The occurrence of periplatform ooze in different stratigraphic levels of the siliciclastic-dominated Vaca Muerta Formation demonstrates that off-shelf transport and distribution of carbonate mud in the basin are also common processes in mixed clastic-carbonate environments.

The making of a new 1000 km Vaca Muerta trunk gas transport pipeline to market destination points: Decree 465/19 and its bidding terms

Abstract This article refers to the extraordinary circumstance of Argentina's holding the second largest shale gas resources in the world, at a time it has been proven that they can be rapidly exploited commercially. The sweeping changes brought by this change of paradigm for a country with declining conventional natural gas reserves in a gas dependent domestic economy require urgent infrastructure expansion to solve bottlenecks to reach domestic and international, markets, to be achieved only through stable market rules and a robust framework for a further trunk pipeline. The incoming bidding for such pipeline and its insertion in the current legal framework is described in detail, regardless of the fact that current government elections may defer the outcome, but not stop this essential infrastructure for the country's development.

Pore system characterization of organic-rich shales using nanoscale-resolution 3D imaging

The Vaca Muerta Shale in Argentina is the first major commercial shale oil/gas play outside of North America. High-resolution 2D/3D imaging of shale rocks for the purpose of establishing their mineralogy, total, and connected porosities has become more and more sophisticated. In this paper, nanoscale-resolution focused ion beam (FIB)–scanning electron microscopy (SEM) nano-tomography was used to obtain images of pore structures within two organic-rich regions of interest (ROIs), selected based on correlative SEM and automated mineralogy maps. Advanced machine learning classification tools were used to segment the images and assign porosities and other components. Pore size distribution and pore connectivity analyzes revealed that about 95% of all the pores, present within the two ROIs, had a diameter of less than approximately 75 nm, and that most of these pores were poorly connected. In a similar fashion, the flow rate distribution analysis showed that pores with diameters of about 150–330 nm contributed to over 50% of the flow capacity of the connected pore systems. These results suggest that although most of the pores typically found in shales have pore diameter smaller than about 100 nm, most of the hydrocarbon production may be carried by a relatively small number of larger connected pores with pore diameter greater than about 150 nm. This study implies that a large portion of the organic-hosted pores (with diameter typically smaller than about 100 nm) may not provide permeable flow pathways for the oil and/or gas migration, and hence may have very little contribution to the hydrocarbon production.

Towards a holistic approach to sustainability in the Argentine Patagonia

PurposeSustainability involves a strong interrelationship of ecological, cultural, technological, scientific, economic and social aspects and deserves to undertake a holistic treatment. Abundant evidence has being collected related to the several risks and conflicts derived from unsustainable oil exploitation and fossil fuel energy sources. In the past few years, several environmentally friendly technologies are being developed for oil exploitation in the Argentine Patagonia. The purpose of this paper is to examine them under a holistic prospect to provide an overall outlook for a wide audience and making it attractive for teaching sustainability in higher education.Design/methodology/approachThe environmentally friendly technologies chosen to be examined are Green Chemistry, cleaner production processes and alternative energy sources. Vaca Muerta, located at Neuquén Basin in Argentine Patagonia, is one of the world’s major deposits of tight oil and shale gas. Fracking technology, required for this exploitation, is controversial; it poses critical issues concerning ecological risks such as oil leakage and serious soil damage.FindingsResearch results on the germination of a native gramineae in polluted soils are described in this paper under several conditions and show its potential for the phytoremediation of damages aroused from unsustainable oil exploitation. In addition, student’s feedback regarding fracking was examined by a questionnaire presenting different and contradictory perspectives with open and Likert-type items. This study complements previous observation on the open acceptance of the Green Chemistry fundamentals as the contribution of the scientific-technological knowledge to the sustainable development and higher education approaches from Argentina.Research limitations/implicationsA clear result of these experiences is that the immediate impact is stronger that that noted when just scientific and technological aspects are taught; teachers expressed they would try to repeat these exercises in their classes in middle and high schools. This feeling of fear is important for people to understand the severity of climate change, though it is also essential to help people move past fear, to use the urgency of the problem to motivate action. Results of this research suggest that the best way to understand climate risks is interactive learning.Originality/valueThis study describes related scientific, technological and societal research in the fields of soil remediation and sustainable production that are key values in higher education, as scientific and societal communities play an essential role. From a holistic approach to a complex problem, this paper describes research on different aspects that converge into the viewing of the radical change in the society’s behavior that is urgently required for a sustainable development in harmony with the planet. In spite of their importance, there are few publications with an interdisciplinary overview about sustainable development in Latin America. The value and originality of this work is that it focuses on the need of teaching sustainability in different areas of higher education with a holistic prospect.

A quick analytical approach to estimate both free versus sorbed hydrocarbon contents in liquid-rich source rocks

Free and sorbed low-to-medium molecular weight thermovaporized hydrocarbons (<C20) are the main organic compounds released at the temperature range corresponding to the Rock-Eval® Shale PlayTMSh0 parameter (100°C–200°C), whereas medium and high molecular weight thermovaporized compounds (< C30) are the predominant components that are thermal released in the temperature range corresponding to the Shale Play Sh1 parameter (200°C–350°C). Now, an analytical methodology is proposed here to predict the quantity of free versus sorbed hydrocarbons still present in any liquid-rich sedimentary rock. The method compares shale play parameters (Sh0 and Sh1) obtained from both whole-rock samples and their corresponding organic matter (OM) concentrates isolated by standard nonoxidizing acid treatments and drying procedures. The hydrocarbon content obtained from whole rock (HCTotal,rock) is mainly considered as the total amount of free liquid hydrocarbons (HCFree) and sorbed liquid hydrocarbons (HCSorbed,OM) still contained in the investigated rock sample. The hydrocarbon content obtained from OM concentrates, however, only reflects the sorbed liquid hydrocarbons. In these equations, TOCrock is the total organic carbon of the rock sample; TOCOM corresponds to the TOC content of the OM concentrate sample; Massrock is the initial mass of the rock sample; MassOM is the initial mass of the OM concentrate sample; FIDsignalrockSh0+Sh1 is the flame ionization detection (FID) signal that corresponds to the global surface area under each thermal peak (Sh0 and Sh1) generated by the Rock-Eval FID; FIDsignalOMSh0+Sh1 corresponds to the global surface area under each thermal peak (Sh0 and Sh1) measured by the Rock-Eval FID between 100°C and 350°C after the themovaporization of the OM concentrate sample. Free liquid hydrocarbons are finally calculated as the difference between these last two values (HCFree e HCTotal,rock − HCSorbed,OM). This paper illustrates the application of this methodology on rock samples derived from the Vaca Muerta Formation (Argentina). Along the selected vertical profile, the lower rock interval contains approximately 60% of sorbed liquid hydrocarbons, whereas the upper sample contains more than 90% free liquid hydrocarbons. The parameters FreeHCSh0 and FreeHCSh0+Sh1 could be used to identify potential producible free liquid hydrocarbons intervals in early exploration campaigns.

Considering Time and Space in Drilling and Completion Can Reduce Well Interference

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 191836, “When, Where, and How To Drill and Complete Pads of Multiple Wells? Four-Dimensional Considerations for Field Development in the Vaca Muerta Shale,”by Stephane Pichon, SPE, Federico Gaston Cafardi Orihuela, Emilio Lagarrigue, and Gustavo Cavazzoli, SPE, Schlumberger, prepared for presentation at the 2018 SPE Argentina Exploration and Production of Unconventional Resources Symposium, held in Neuquén, Argentina, 14–16 August. The paper has not been peer reviewed. Development of organic shale reservoirs with large hydraulic-fracture treatments not only poses challenges to the completion of a single well, but also to interference with surrounding wells. A direct consequence of interference is production loss. Therefore, the drilling and completion schedule for field development must be 4D in time and space to account for interaction in between wells. The complete paper describes a physics-based model of interference and a sensitivity study to propose guidelines for well spacing and a drilling timeline for multiple horizontal wells in the Vaca Muerta shale. Introduction Effective field development relies on the tradeoff between the capital expenditure (CAPEX) and the production profile generating cash flow. Both CAPEX and the production profile are directly controlled by the number of wells and the pace at which these wells are tied in to the production facilities. With respect to tight rocks, the need for horizontal drilling and hydraulic fracturing adds a layer of geometrical complexity to unlock such resources. In very-low-permeability reservoirs, the drainage area is controlled by the hydraulic-fracture geometry. However, the relatively large size of the fracturing treatments performed in a multistage manner across several different perforation clusters within a same stage makes hydraulic fractures difficult to control. In practice, fracture dimensions are not constant along a lateral. Additionally, because limited contribution of the matrix is expected in a nano-Darcy environment, the spacing between laterals tends to be smaller than the reach of the hydraulic fractures. This has been evidenced by the increasing concern over fracture hits in the industry, and already has been experienced in the Vaca Muerta. Interference can be caused by fracture hits while completing the well, competition for drainage area during production, or fracture-geometry deterioration caused by stress field variation when infill-drilling a child well near a produced parent well. Even if some overlap between the hydraulic fractures of two neighboring wells is advisable to avoid leaving reserves behind, the tradeoff between well spacing, completion intensity, and production interference remains a delicate exercise. Hydraulic fracturing should be considered at the field level, rather than independently for each well, giving completion a multiple-well spatial dimension. As an additional complexity, child wells completed later in the development of a lease tend to perform more poorly than the parent wells. This performance impairment might have several different sources, but one of the most-accepted hypotheses is that the heterogeneous contrast in the stress field generated by the depletion around the parent negatively affects the contact area provided by the hydraulic fractures of the child well.

Igneous petroleum systems in the Malargüe fold and thrust belt, Río Grande Valley area, Neuquén Basin, Argentina

Abstract The Rio Grande Valley (Neuquen Basin, Argentina) is a large oil field where voluminous igneous sill complexes are emplaced in different levels of the sedimentary sequence in a fold and thrust belt setting. These sills are predominantly emplaced in organic-rich units such as Vaca Muerta and Agrio Formations and are critical elements of the defined petroleum system, as they affect the thermal maturity of the surrounding source rocks, and also act as naturally fractured reservoirs. In this contribution, we integrated structural sections, borehole data, core descriptions, petrophysical laboratory tests and organic geochemistry measurements to characterize the impact of the magmatism in the petroleum system of the Rio Grande Valley oil field. Especially, we focused in evaluating the impact of the sill-complexes in hydrocarbon generation, migration and accumulation. Our data shows that: (1) intrusions are preferably emplaced in organic rich units; (2) a large number of intrusions is observed in areas intensely deformed by imbricated thrusts; (3) an increase in the number of intrusions drives stronger and more extensive maturation processes in the Vaca Muerta formation, enhancing notably the cracking of kerogen to hydrocarbon within this unit; (4) where the number of intrusions increases, the concentration of total gas and methane also increases, given that all sills are suitable reservoirs; (5) igneous rocks provide a low resistance path for fluids flow and act as the main reservoirs in the study area; (6) the reservoir quality of igneous intrusions is dominated by the combination of matrix and fracture framework properties; (7) zeolites are the most common type of cement in these reservoirs; (8) deep sills located in the Vaca Muerta formation produce larger volumes of hydrocarbons relative to shallower intrusive reservoirs. The Rio Grande Valley oil field offers a world-class example of the implications of igneous complexes in hydrocarbon generation, migration and accumulation in a compressive tectonic setting of fold and thrust belt.

E&amp;P Notes (August 2019)

E&amp;P Notes (August 2019)

Limitations for Compositional Modeling in Vaca Muerta Numerical Simulation

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 191822, “Vaca Muerta Numerical Simulation: A Warning in Compositional Modeling,” by Sergio Bosco, Mariano Suarez, SPE, and Elisabet Savoy, SPE, YPF, prepared for the 2018 SPE Argentina Exploration and Production of Unconventional Resources Symposium, Neuquén, Argentina, 14–16 August. The paper has not been peer reviewed. Vaca Muerta formation fluids run from medium black oils to very dry gas, according to source-rock maturity. High-shrinkage volatile oil and very rich gas condensate are found and compositional variation is areally continuous. Despite this huge difference in fluid nature, where saturation pressures are present, more than 200 kg/cm2 undersaturation is reported. Because of the complex dependence of fluid behavior with composition for near-critical gas condensate and volatile oil, the use of compositional modeling is mandatory. Cubic equations of state (CEOS) are the only types implemented until now in commercially available compositional numerical simulators. In this paper, the authors show the limitation of CEOS for modeling reservoir behavior of liquid-phase black and volatile oil in highly undersaturated reservoirs. Introduction The Vaca Muerta shale, located in the Neuquén Basin, Argentina, ranks among the top shale oil and gas resources in the world. It is characterized by its areal extent, high gross thickness, and high organic content. The first well was drilled and completed in 2010 and despite more than 650 wells to date, Vaca Muerta shale history is relatively recent compared with other known shale plays. Source-rock thermal maturity seems to be the main driver for fluid distribution, running from dry gas in very mature zones, progressing through gas condensate and volatile oil, to black oils of less than 100 m3/m3 gas/oil ratio (GOR) in immature zones. Production forecasts on new wells are based primarily on the history of geographically close wells, but forecasts for new zones involve numerical simulation of regionally distributed properties, including reservoir-fluid characteristics. The original aim of the work described in this paper was the equation of state (EOS) description of the pressure/volume/temperature (PVT) properties of fluids in known zones, to use in extrapolation to those zones where information is sparse. The models and work flows described in papers SPE 177058 and URTeC 2436107 were the starting point for this paper; in those earlier works, the authors aimed to extend the work flow into more complex fluids. An extensive EOS fitting program was launched. Surface and subsurface samples were taken for fluid characterization and PVT tests were performed for each. All presented, at least, 200 kg/cm2 of undersaturation (Fig. 1).

Work Flow Uses Vaca Muerta Data To Optimize Asset Evaluation

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 191272, “Optimization Under Uncertainty for Reliable Unconventional Play Evaluation: A Case Study in Vaca Muerta Shale Gas Blocks, Argentina,” by Reza Mehranfar, Leonardo Marquez, SPE, Raphael Altman, SPE, Hassan Kolivand, Rodrigo Orantes, and Oswaldo Espinola, SPE, Schlumberger, prepared for the 2018 SPE Trinidad and Tobago Section Energy Resources Conference, Port of Spain, Trinidad and Tobago, 25–26 June. The paper has not been peer reviewed. Asset evaluation embraces the integrated analysis of a hydrocarbon-bearing field, and the identification of suitable strategies for its future development, to add incremental value for the investor(s). Optimizing the evaluation process under uncertainty is important particularly in unconventional reservoirs, which hold large quantities of oil and gas resources but also exhibit large degrees of uncertainty. This paper describes a comprehensive optimization-under-uncertainty work flow that combines a simulation-based approach with semiautomatic work flows and high-speed computers to facilitate the process of decision-making for investors, using data from the Vaca Muerta Formation in Argentina as an example. Introduction An asset evaluation depends on many input parameters, some of which are partially known, partly analyzed, or un-available. Yet a go/no-go decision must be made, frequently within short time frames, because of competition, changing conditions, or the chance to take advantage of the business opportunity. The decision usually is based on preliminary assumptions and a conscientious analysis of several possible outcomes. Identifying the suitable future development strategies and the estimation of un-certainties in the input variables is crucial. Knowing the possible variability of the input and how the field mechanisms function will allow probabilistic forecasts of parameters such as production, costs, prices, and revenues. In the case of unconventional reservoirs with very limited history and high development costs, optimization under uncertainty plays a significant role in maximizing profit, reducing investment risk, and facilitating the decision-making process. The authors summarize the optimization-under-uncertainty work flow that was implemented for this study. The starting point is the development of a base-case, single-well, matched simulation model, and, where available, an extended model with history-matched offset wells. This is followed by sensitivity analysis to identify the most-influential parameters; uncertainty analysis and proxy modeling for developing probabilistic forecasting profiles (type wells); and optimization of key parameters under existing uncertainty, which is the final objective of this paper. The model and the uncertainty and optimization work flows have been built in the Petrel platform and all the simulations have been executed in the Eclipse compositional reservoir simulator, using published Vaca Muerta data. Base-Case Single-Gas-Well Model A critical element of any single-well simulation study is developing a base-case simulation model that correctly captures all the fluid-flow mechanisms that take place during the life of the well, while running as fast as possible. The characteristics of the base-case single-well simulation model and the mechanisms that were considered are discussed briefly, because the main objective of this work was to focus on probabilistic forecasting and optimization.