Vaca Muerta Shale Research Articles

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 The paper has not been peer reviewed.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).

Technology Focus: Unconventional Resources (July 2019)

Technology Focus The charge of a JPT Technology Focus reviewer is not only to select the best SPE papers encountered over the past year but also to identify potential ways in which these papers, and the technology contained therein, can assist the growth of industry professionals. While all of JPT’s feature topics are of great importance to the industry, the technical attention and economic importance attached to unconventional plays in recent years stresses a need for appropriately unconventional thinking. For this year’s feature, the selected papers provide innovative work flows that assist in determining productivity, reduce the effect of uncertainty conditions, and spark rejuvenation. The first of these, paper SPE 190860, emphasizes the importance of an effective lateral-landing strategy in enhancing long-term reservoir productivity and provides a work flow that uses a suite of integrated data to achieve consistent results that can aid in field management and ultimate recovery estimates. Paper SPE 191272 uses a case study from the Vaca Muerta Shale in Argentina to demonstrate the efficacy of a work flow that uses a simulation-based approach combined with high-speed computing to improve investor confidence. The authors stress in particular the need to characterize the correct variables and to establish the range of their uncertainty. Finally, paper SPE 191457 introduces an integrated work flow that couples geomechanical effects and reservoir-simulation modeling in the effort to rejuvenate unconventional plays, stressing interpretation of the variables that can affect the development of the simulated reservoir volume. These three innovative papers represent, as always, the skill and vision of industry professionals like yourself as we continue to learn from, and add to, the body of technical knowledge that SPE represents. I hope that you enjoy the papers. Recommended additional reading at OnePetro: www.onepetro.org . SPE 191923 Alleviating the Solids Issue in Surat Basin in Coal-Seam-Gas Wells by Daniel Kalinin, Schlumberger, et al. SPE 192010 Optimizing Horizontal Coal-Seam-Gas Wells by Combining Reservoir Simulation and Transient Well Modeling by Turaj Nuralishahi, APLNG, et al. SPE 192694 First Global Successful Large-Diameter Pressurized Coring Application Using High-Performance Water-Based Mud: Kuwait Case History by Robin Stewart, Halliburton, et al.

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.

E&P Notes (February 2019)

E&P Notes (February 2019)

AVO inversion on unconventional reservoirs: systematic estimation of uncertainty in the Vaca Muerta shale

Abstract Amplitude versus offset inversion is widely used in reservoir characterization, but its implementation on unconventional reservoirs represents a challenge owing to the subtle changes of elastic parameters that demarcate profitable areas. For this reason, it is important to have an estimation of the uncertainty expected from seismic inversion to improve the interpretation of inverted results. We have implemented a systematic estimation of uncertainty of relative elastic properties obtained by damped least squares inversion of Aki and Richards and Fatti et al. approximations of Zoeppritz’s equation. Well log data of the Vaca Muerta unconventional shale in Argentina was used to generate synthetic angle gathers, varying in terms of asignal-to-noise ratio, range of angle coverage and number of partial angle stacks. The inversion results provide a systematic estimation of the uncertainty of the inverted coefficients. Results show that signal-to-noise ratio and range of angle coverage of the seismic data are key parameters to assess the feasibility of the inversion. In case of characterization based on acoustic impedance, the inverted parameters show good correlation with the model, with these correlation values being predicted by the parameter resolution matrix values.

Microseismic monitoring of Vaca Muerta completions in the Neuquén Basin, Argentina

The Vaca Muerta shale oil play in Argentina's Neuquén Basin is expected to make a large contribution to Argentina's hydrocarbon production in the future. In 2013, the U.S. Energy Information Administration estimated that the Vaca Muerta had technically recoverable reserves of 308 Tcf gas and 16 billion bbl of oil and condensate, making it the third largest shale oil reservoir in the world at that time. Wintershall Energia has been active in the Neuquén Basin since 1994. In 2014, it acquired a controlling interest in the Aguada Federal block with an intention to exploit the Vaca Muerta oil shale occurrence within that block. At the outset of its development program, Wintershall decided to incorporate microseismic monitoring to help understand completions in the Vaca Muerta. Monitoring of the completion of vertical well AF.x-1 was accomplished with a surface array. The goal of the monitoring was to inform later decisions on horizontal wellbore direction, wellbore and stage spacing, and landing depth. Results of the surface array monitoring were also used in the design of a permanent buried array intended to monitor subsequent development wells. The buried array was installed in September 2016 and consists of 126 stations spread at an interval distance of approximately 500 m over an area of roughly 5 by 7 km. Each station has geophones placed over a depth range of 20 to 50 m subsurface. The first two horizontal development wells in the project, AF.x-4h and AF.x-9h, were completed in late December 2016 and early January 2017. The second set of two wells, AF.x-3h and AF.x-7h, was completed from May to June 2017. The 4h and the 7h were landed in the upper Middle Vaca Muerta while the 9h and 3h were drilled about 100 m deeper, landing still in the Middle Vaca Muerta. The lateral length of each well was approximately 1000 m, and each was completed with 11 plug-and-perf stages. Stage length and interval were varied along the wells to test various completion strategies. The completions of all four wells were successfully monitored using the buried array. These microseismic data provide a detailed description of the fracture network created by the treatments. Focal mechanisms determined for the detected events have been used to understand the stress distribution in the reservoir and to further refine the completion parameters for future development wells.

Application of proxy-based MCMC and EDFM to history match a Vaca Muerta shale oil well

Embedding complex discrete fractures in reservoir simulation is required to attain more realistic flow behavior of shale reservoirs. However, using local grid refinement to model discrete fractures is computationally expensive. Nevertheless, recent developments in a methodology called Embedded Discrete Fracture Model (EDFM) have overcome the computational complexity. In this study, we develop an efficient assisted history matching (AHM) workflow using proxy-based Markov chain Monte Carlo algorithm and integrating with the EDFM preprocessor. The workflow can automatically perform history matching, production forecasting and uncertainty quantification. It has been successfully applied on a shale oil well in Vaca Muerta formation.

Comments: The Vaca Muerta

Editor's column Argentina’s Vaca Muerta shale play is considered one of the most promising unconventional resources in the world. Advertised for years as the next great shale resource outside of the US, foreign investment has now picked up and the play may finally begin living up to its potential. A comprehensive article beginning on page 26 outlines the current state of the Vaca Muerta, including geological and business challenges, as well as future development plans. Total output from Vaca Muerta in barrels of oil equivalent (BOE) has risen 60% since the start of 2016. Production is currently just over 75,000 BOE/D—split roughly evenly between oil and gas—but most of the money spent in the play so far has been in exploration; output is expected to rise sharply over the next decade. Most of the current output comes from the Loma Campana joint venture between YPF and Chevron, but other projects may ramp up soon. Production is expected to rise to 113,000 BOE/D by the end of this year, and as high as 1 million BOE/D within 15 years, according to consultancy Wood Mackenzie. The shale rock in Vaca Muerta is considered very high quality, on a par with several US shale plays such as Eagle Ford, Bakken, and Marcellus. Government-led reforms have been a major factor in its growth, in part because the country needs the economic benefits of Vaca Muerta. Once an energy exporter with a sound economy, Argentina last decade defaulted on $82 billion of foreign debt—the largest such default in history at the time. Elected president in 2015, Mauricio Macri vowed to put Argentina on sounder financial footing, and has his eye on replicating the shale boom in the US. After October’s elections consolidated his political power, he has embarked on a campaign to get international oil companies and domestic ones to up their investments in the shale play. More than 15 companies are currently exploring in the Vaca Muerta, including big names such as Chevron, ExxonMobil, Total, and Shell. YPF and the government are also working to lower labor costs. Trade unions made concessions on contracts in exchange for commitments on spending, which the government said could cut development costs by 20%. YPF has announced a $30-billion, 5-year investment plan for Vaca Muerta, and ExxonMobil has committed $200 million to a pilot project there. Before the country’s historic default, Argentina was a net exporter of oil and gas but lack of investment has turned it into an energy importer. Argentina’s oil production hit 489,000 B/D last year, down sharply from a peak of 847,000 B/D in the late 1990s. Gas output peaked at 4.5 Bcf/D in 2005 and is now roughly 3.7 Bcf/D. The US Energy Information Administration estimates that Argentina has the world’s second-largest shale gas and fourth-largest oil resources. If the current momentum continues, Vaca Muerta may become the only viable shale play outside of North America.

Integrated Completion Sensitivities for Horizontal-Well Design in the Vaca Muerta

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 185499, “Fracturing-to-Production Integrated Completion Sensitivities for Horizontal-Well Design in the Vaca Muerta Shale,” by S. Pichon, F. Cafardi, G.D. Cavazzoli, A. Diaz, and M.R. Lederhos, Schlumberger, prepared for the 2017 SPE Latin America and Caribbean Petroleum Engineering Conference, Buenos Aires, 17–19 May. The paper has not been peer reviewed. The boom in organic shale plays has revealed the critical need to size hydraulic-fracture treatments correctly to achieve commercial success. The right balance must be found between the cost of fracturing and the additional production achieved by increasing the formation-to-wellbore contact area. The complete paper examines a range of completion scenarios to evaluate the relationship between hydraulic-fracture design, production, and well profitability by use of numerical simulations to guide completion of horizontal wells in Argentina’s Vaca Muerta Shale. Introduction The Vaca Muerta Shale is the source rock of most of the producing formations in the Neuquén Basin, with high potential as a standalone reservoir. The first well aiming at testing production from the play was drilled and completed in 2010, and, at the end of 2016, the production from the formation involved more than 600 wells. Well-construction practices have moved from creating vertical wells to creating horizontal wells. In any organic shale play, completion has a significant weight in the total well cost and must be sized adequately. Completion design is composed of the volume and number of hydraulic fractures to be created along the lateral, and it must be engineered according to the specific features of each formation. One of the principal features of an organic shale reservoir is the absence of commercial production unless the well is hydraulically fractured. Enhancing the contact area between the formation and the wellbore with hydraulic fractures compensates for the extremely low permeability of these formations. Multiple factors, including geomechanics and stress direction, drive the geometry of the hydraulic fractures. However, it must be noted that most organic shale reservoirs are overpressured. This factor tends to drive the stresses up and reduce their horizontal anisotropy. Besides the hydraulic-fracture geometry, production is also the result of the hydrocarbon volume in place and the interaction of the flow capacities between the reservoir and the created network of conductive fractures. Therefore, the size of this surface of exchange created by the hydraulic fractures has a critical effect on the level and dynamics of the production profile. Finally, economics is the balance between total well cost and production. The completion design affects both production and total well cost, making it a critical parameter. Fracturing-to-Production Integrated Work Flow Work-Flow Requirements. With the primary objective being the combined evaluation of completion design, hydraulic-fracture geometry, production, and economics, the methodology must allow an explicit description, at either the input or output level, of each one of the aforementioned parameters. The fracturing-to-production work flow fits this purpose and is proposed for this study. The work flow has been implemented successfully in the Vaca Muerta and various other shale plays.

Technology Focus: Completions (September 2017)

Technology Focus I am very excited to begin my term as editorial reviewer for Completions. JPT has always been the source of cutting-edge information on industry technology developments, and I pledge to continue that tradition through expert review and selection of articles. Our industry is showing signs of emerging from the recent downturn, and commodity prices are slowly improving. There is intense focus across the industry on profitability in the current low-oil-price environment, and profitability must be achieved while meeting regulatory requirements, delivering value to stakeholders, and attracting and retaining the best talent available. Yet, today’s profitability is not the only challenge. Laying the groundwork for future profitability must also occur. One of the more powerful tools available to help achieve sustained profitability is innovation, and it has consistently generated cutting-edge technologies that have advanced the oil and gas industry. The good news is that innovation has continued during the downturn. For example, advancements in dissolvable-materials technology and downhole data acquisition have continued. While the former primarily advances efficiency in multizone shale well completions, the latter will advance effectiveness in both land and offshore completions. Process innovation is also occurring and is evident in the drive to create advanced numerical models for optimization of stimulation and hardware choices in multizone shale well completions. Finally, increased focus on reliability in design, installation, and operation has emerged, as both operators and suppliers recognize the contribution of risk management to completion technology and systems. The articles in this month’s Completions section are great examples of how innovation is driving profitability, and I hope that they help you drive profitability in your completions. Recommended additional reading at OnePetro: www.onepetro.org. IADC/SPE 180542 Appropriate Completion To Prevent Potential Damage of Annular Pressure Buildup in Deepwater Wells by Bo Zhang, China University of Petroleum, et al. SPE 185499 Fracturing-to-Production Integrated Completion Sensitivities for Horizontal-Well Design in the Vaca Muerta Shale by S. Pichon, Schlumberger, et al. SPE 185051 The Impact of Completion Technique on Well Performance by D.M. Anderson, Anderson Thompson Reservoir Strategies, et al.

Unconventional Resources Technology Conference Highlights Shale as an International Business

Unconventional Resources Technology Conference Highlights Shale as an International Business

Integration of Dynamic Microseismic Data With a True 3D Modeling of Hydraulic-Fracture Propagation in the Vaca Muerta Shale

SummaryMicroseismic mapping during the hydraulic-fracturing processes in the Vaca Muerta (VM) Shale in Argentina shows a group of microseismic events occurring at shallower depth and at later injection time, and they clearly deviate from the growing planar hydraulic fracture. This spatial and temporal behavior of these shallow microseismic events incurs some questions regarding the nature of these events and their connectivity to the hydraulic fracture. To answer these questions, in this article, we investigate these phenomena by use of a true 3D fracture-propagation-modeling tool along with statistical analysis on the properties of microseismic events.First, we propose a novel technique in Abaqus incorporating fracture intersections in true 3D hydraulic-fracture-propagation simulations by use of a pore-pressure cohesive zone model (CZM), which is validated by comparing our numerical results with the Khristianovic-Geertsma-de Klerk (KGD) solution (Khristianovic and Zheltov 1955; Geertsma and de Klerk 1969). The simulations fully couple slot flow in the fracture with poroelasticity in the matrix and continuum-based leakoff on the fracture walls, and honor the fracture-tip effects in quasibrittle shales. By use of this model, we quantify vertical-natural-fracture activation and fluid infiltration depending on reservoir depth, fracturing-fluid viscosity, mechanical properties of the natural-fracture cohesive layer, natural-fracture conductivity, and horizontal stress contrast. The modeling results demonstrate this natural-fracture activation in coincidence with the hydraulic-fracture-growth complexities at the intersection, such as height throttling, sharp aperture reduction after the intersection, and multibranching at various heights and directions.Finally, we investigate the hydraulic-fracture intersection with a natural fracture in the multilayer VM Shale. We infer the natural-fracture location and orientation from the microseismic-events map and formation microimager log in a nearby vertical well, respectively. We integrate the other field information such as mechanical, geological, and operational data to provide a realistic hydraulic-fracturing simulation in the presence of a natural fracture. Our 3D fracturing simulations equipped with the new fracture-intersection model rigorously simulate the growth of a realistic hydraulic-connection path toward the natural fracture at shallower depths, which was in agreement with our microseismic observations.

Custom-Designed Coiled Tubing Leads to Success in Extended-Reach Operations

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 184752, “Vaca Muerta Coiled-Tubing-Operations Success and the Development of Future Extended-Reach Operations,” by I.I. Galvan, Global Tubing; M.M. Nebiolo, R.D. Del Negro, and G.A. Landinez Gomez, YPF; C. Cerne, SPE, ThruTubing Solutions; and A. Sanchez, SPE, and G. Mallanao, Global Tubing, prepared for the 2017 SPE/ICoTA Coiled Tubing and Well Intervention Conference and Exhibition, Houston, 21–22 March. The paper has not been peer reviewed. Advanced horizontal drilling, multistage hydraulic fracturing, and other technologies have helped make the Vaca Muerta shale oil and gas resource economically viable. An option to exploit this resource better is to increase the length of the horizontal section of each well to add hydraulic-fracture stages. Anticipated high angles in deviated well sections, along with the extended horizontal length of the planned wells, formed an expectation that conventional coiled-tubing (CT) designs would not be able to service the new well designs. Using refined, custom-engineered CT-string designs appears to be an economic and efficient solution. Project Overview Increased diameter, strength, and reliability have made CT the preferred cost-effective well-intervention solution in the Vaca Muerta unconventional shale development; however, the maximum lateral reach the CT can achieve during operations is a limiting factor for well optimization. Initially, 2-in. CT strings with a simple wall taper shape were an effective and reliable option to complete wells in the first development stage. However, the need for optimized design and even-larger-diameter CT with enhanced-wall-thickness configurations became apparent when an increase of the well lateral lengths was attempted. CT-String Design Considerations The CT-string designs followed a cooperative process between the operator, the CT service companies, tool providers, and the CT-manufacturing engineers. Tubing forces, buckling occurrence, and lockup depths were analyzed in detail to determine the optimal CT size and string design makeup to ensure the likelihood of reaching target depth (TD) in the planned extended-reach wells. Additionally, hydraulic analysis was performed to compare frictional pressure losses (CT, bottomhole-assembly, and annular) using the optimal flow rates for annular velocities adequate to support sufficient well cleaning. The results from the analysis were used to estimate fatigue accumulation in the CT strings, considering anticipated circulating pressures and surface-equipment (reel and gooseneck arch) dimensions. The primary objective for the new CT-string design is to optimize lateral reach and available weight on bit for post-fracture mill-out operations.

Optimism and Activity Rising in the Vaca Muerta

Optimism and Activity Rising in the Vaca Muerta Confidence in the geologic potential of Argentina’s unconventional resource plays is higher than ever, which is turning the focus to how and when oil and gas producers there will ramp up commercial levels of production. At stake is whether the well-known Vaca Muerta formation will become a shale superpower—and the first outside of North America. Its immense reserves, estimated to be 308 Tcf of gas and 16 billion bbl of oil, according to the US Energy Information Administration, and the work done so far to prove them has attracted commitments of billions of dollars from international majors BP, ExxonMobil, Shell, and Chevron. But leading the pack is the domes-tic explorer and producer Yacimientos Petrolíferos Fiscales (YPF). The company’s progress may offer a reasonable expectation of what the future holds. Operating more than 540 shale wells in the Vaca Muerta and running 44 rigs at the end of last year, YPF has been by far the most active shale operator in Argentina. Eighty of those wells are horizontals in the Loma Campana field, operated as a joint venture with Chevron. The first were drilled and completed there in 2013, and the most recent have shown an average productivity increase of 25%, a figure based on 300 days of production data. In all, YPF drilled 56 horizontals last year, showing that it has picked up the pace compared with 2015 when 30 were drilled and the 2 years prior when a combined five were drilled. The gas portion of the 62,300 BOED YPF is reporting in gross shale production (which includes areas outside Loma Campana) represents 22% of its total natural gas production. That will be an important piece of the pie chart to track going forward because the majority of YPF unconventional programs, and those of its competitors, have become increasingly focused on boosting Argentina’s gas supplies. This is a shift from the initial programs that targeted the oil window and is being driven by a newly elected government that is aiming to reverse the country’s position as a net importer of gas. EOR Project in the Vaca Muerta Shale Gives Water for Oil New research from Argentina is trying to see if the Vaca Muerta shale formation is a viable candidate for enhanced oil recovery (EOR). The laboratory and field experiments completed so far are promising, which in itself is a notable development since there have been very few breakthroughs on this front for the shale sector. The companies leading this work, Buenos Aires-based VYP Consultores and InLab, are using a simple huff-and-puff approach to shale EOR that involves injecting produced water back into a well for a soaking period of 30 days. During this time, with the well shut in, the formation does most of the work through imbibition; i.e., the water goes into the formation, and exchanges places with hydrocarbons.

Completion and Well-Spacing Optimization for Horizontal Wells in Pad Development

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 180956, “Completion and Well-Spacing Optimization for Horizontal Wells in Pad Development in the Vaca Muerta Shale,” by M. Suarez, SPE, YPF, and S. Pichon, SPE, Schlumberger, prepared for the 2016 SPE Argentina Exploration and Production of Unconventional Resources Symposium, Buenos Aires, 1–3 June. The paper has not been peer reviewed. In organic shales, hydraulic fracturing is important for optimizing the production of horizontal wells. For a standalone lateral, the propped surface should be maximized to increase production. In the case of a pad, well spacing is an additional factor. Competition for production between laterals of a given pad should be minimized and is the result of both well spacing and hydraulic-fracture design. A numerical model coupling an explicit description of the hydraulic-fracture geometry and reservoir simulation is proposed to evaluate production interference. Introduction Well Spacing. One of the more critical questions that any asset team must consider concerns well spacing when designing the development plan for a new field. Well spacing defines the total number of wells, the drilling and completion schedule, and the field-production curve. The ultimate decision relies on economic analysis, balancing the expected ultimate recovery against capital and operational expenditures. This work focuses on methods to evaluate different well spacing and on how to reduce the range of uncertainty in the development of the Vaca Muerta play. Well-Spacing Evaluation. Well spacing depends on geomechanics, petrophysics, stimulation design, hydraulic-fracture geometry, and reservoir fluids. These factors are combined by use of numerical simulation to study their effects on the well spacing. The following are some of the methods that are applied to define possible well spacing. Analogs. Using analog methods requires an older field already in development with similar rock and fluid quality, structural complexity, well architecture, and hydraulic-fracture stimulation. The analog approach leads to large uncertainties if any of these parameters are not within the same range or if the older analog field does not have sufficient statistical representation. Simple Reservoir Description Without Explicit Hydraulic-Fracture Description. The first step in simulation is to start with a simple reservoir description in which each property is uniform (porosity, permeability, and fluid saturations). The reservoir model is then coupled with an analytical or numerical production simulator. This kind of approach is appropriate for a field with minimal information. The hydraulic fractures are represented as parallel planes that intersect the wellbore. Hydraulic-fracture properties are kept constant over their whole surface and along the lateral.

Shale gas plays, Neuquén Basin, Argentina: chemostratigraphy and mud gas carbon isotopes insights

ABSTRACT: In order to enhance the knowledge of shale objectives from Vaca Muerta and Los Molles Formations in the Neuquén Basin, Argentina, chemostratigraphic and mud gas carbon isotope analyses were performed in two wells from Agua del Cajón and Salitral oilfields (ADC-1016 and NqSa-1148). Geochemical data show restricted levels in both cases to perforate and produce. In ADC-1016 well, Lower Los Molles Formation looks like the most suitable play to be produced. At El Salitral oilfield (NqSa-1148), the best remarkable Vaca Muerta-Quintuco objectives are associated with authigenic elements, in limited horizons. Enhancement of the Quintuco reservoir by deep circulating fluids (thermobaric reservoir) is suggested. Carbon isotope analysis reveals complex processes that affected the gas composition. Addition of microbial methane, biodegradation of ethane-propane and mixing of gases has been recognized. Isotope reversals and presumed water reforming of hydrocarbons have been registered associated with overpressure for Lower Los Molles Formation in the ADC-1016 well, which is pointed out as the most promising shale play in the area. Vaca Muerta gases at Agua del Cajon ADC- 1016 well are associated with the homonymous source. El Salitral 1148 well shows that primary isotope composition in gases from Vaca Muerta shale play and Quintuco reservoir could be associated with a Lower Los Molles source, an aloctonous charge related with the main structures of the area.

Conditioning Mature Vertical Wells To Stimulate and Test Shale Productivity

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 172724, “Conditioning Pre-Existing Old Vertical Wells To Stimulate and Test Vaca Muerta Shale Productivity Through the Application of Pinpoint Completion Techniques,” by Pablo Forni, Capex, and Juan C. Bonapace, Federico Kovalenko, Mariano N. Garcia, and Federico Sorenson, Halliburton, prepared for the 2015 Middle East Oil & Gas Show and Conference, Manama, Bahrain, 8–11 March. The paper has not been peer reviewed. One of the most promising targets for resource-rock stimulation in South America is the Vaca Muerta (VM) shale in western Argentina. It is common practice for operators to begin exploration projects with vertical wells; however, in the Neuquina basin, most already-existing vertical wells are not viable candidates to assess the VM because they were not designed as shale-type completions. This paper discusses the preparation of a well originally drilled in 1974 to allow for the new objective of hydraulic fracturing the VM shale, to test the productivity of its different intervals. Introduction This field consists of three main formations— Los Molles, Tordillo, and Lajas—and oil is produced in the northern part, known as Agua del Cajon. In the Agua del Cajon area, the VM formation consists of mudstones and, very sparingly, wackestones. The maximum temperature and productivity-index (PI) values indicate that the thickness of the center and northern area is in an oil window, while southward is an early oil window or an immature formation. The Agua del Cajon has two distinct areas for its history and development—a central zone gas, currently in full production (El Salitral field) and a north zone (Agua del Cajon), the drilling and exploitation of which were very active in the 1970s and 1980. Development was completed with a secondary-recovery operation in the 1990s. The latter zone had approximately 30 wells, which had exhausted their economic output from productive areas.

E&P Notes (June 2015)

E&P Notes “Regulatory Compliance Just One Reason for Groundwater Sampling” The US Department of the Interior encourages the practice of baseline groundwater sampling before drilling, according to its recently released hydraulic fracturing regulations. Although the practice will not be legally required across all federal lands, there are additional reasons to conduct groundwater sampling, said Ryan Leatherbury, client service manager at environmental engineering firm Weston Solutions. The most obvious reason for sampling is for use as a form of “cheap insurance” against water contamination claims, said Leatherbury, who spoke at a recent SPE Gulf Coast Section Waste Water Management Study Group meeting. “Argentina Expands Research on Shale and Mature Fields” Although Argentina is home to what is probably the largest shale formation in South America, the country remains a net importer of oil and gas, according to the US Energy Information Administration. To produce more hydrocarbons from the Vaca Muerta shale and increase recovery in other domestic plays, the country’s majority state-owned oil company YPF, created a separate research organization called YPF Tecnologia (Y-TEC) in 2012. At present, the research company’s main location is in La Plata, Argentina, 70 km south of Buenos Aires. The construction of a 129,000-ft2 laboratory complex in nearby Berisso will be completed before the end of the year, said Gustavo Galliano, manager of communications and knowledge management and technology liaison at Y-TEC. “A New Map for Composite Design and Testing” Researchers at Rice University in Houston are hoping their new theory on composite properties may help the oil and gas industry reduce the time it takes to develop and test new materials. After 3 years of work, the researchers have created a design map that predicts strength, stiffness, and toughness of different materials when they are layered onto one another. Applications for this theoretical map may include pipes, downhole tools, and marine drilling risers, and especially those that are exposed to high-pressure/ high-temperature environments. To develop the map, the research team looked to nature. Rouzbeh Shahsavari, an assistant professor in the Department of Civil and Environmental Engineering at Rice, said that designing composites that are strong, tough, and lightweight is a big challenge for the materials science world. “Wastewater Recovery a Common Challenge for Aerospace and Oil Industries” While wastewater reuse is an option for oil and gas operations, it is an imperative for space travel. With payload weight at a premium, recycling is the only way to provide potable water for journeys longer than a few days, said Mark Jernigan, executive director of Rice Space Institute at Rice University and associate director, exploration systems development, human health and performance directorate at NASA’s Johnson Space Center (JSC). “The desire for NASA is to reclaim water so we don’t have to bring so much,” said Jernigan, who spoke at a meeting of the SPE Gulf Coast Section’s Waste and Water Management Study Group.

Radial patterns of bitumen dykes around Quaternary volcanoes, provinces of northern Neuquén and southernmost Mendoza, Argentina

Where the Neuquén Basin of Argentina abuts the Andes, hundreds of veins of solid hydrocarbon (bitumen) are visible at the surface. Many of these veins became mines, especially in the last century. By consensus, the bitumen has resulted from maturation of organic-rich shales, especially the Vaca Muerta Fm of Late Jurassic age, but also the Agrio Fm of Early Cretaceous age. To account for their maturation, recent authors have invoked regional subsidence, whereas early geologists invoked magmatic activity. During 12 field seasons (since 1998), we have tracked down the bitumen localities, mapped the veins and host rocks, sampled them, studied their compositions, and dated some of them. In the provinces of northern Neuquén and southernmost Mendoza, the bitumen veins are mostly sub-vertical dykes. They tend to be straight and continuous, crosscutting regional structures and strata of all ages, from Jurassic to Palaeocene. Most of the localities lie within 70 km of Tromen volcano, although four are along the Rio Colorado fault zone and another two are at the base of Auca Mahuida volcano. On both volcanic edifices, lavas are of late Pliocene to Pleistocene age. Although regionally many of the bitumen dykes tend to track the current direction of maximum horizontal tectonic stress (ENE), others do not. However, most of the dykes radiate outward from the volcanoes, especially Tromen. Thicknesses of dykes tend to be greatest close to Tromen and where the host rocks are the most resistant to fracturing. Many of the dykes occur in the exhumed hanging walls of deep thrusts, especially at the foot of Tromen. Here the bitumen is in places of high grade (impsonite), whereas further out it tends to be of medium grade (grahamite). A few bitumen dykes contain fragments of Vaca Muerta shale, so that we infer forceful expulsion of source rock. At Curacó Mine, some shale fragments contain bedding-parallel veins of fibrous calcite (beef) and these contain some bitumen, which is geochemically of low grade. In contrast, a large crosscutting bitumen dyke is of higher grade and formed later. At other localities, near basement faults, bitumen dykes have cap-rocks of hydrothermal calcrete. Other dykes or their wall rocks contain hydrothermal minerals. Finally, some dykes splay upward towards the current land surface. We conclude that (1) the bitumen dykes formed during volcanic activity in Pliocene–Pleistocene times, and that (2) heat advection by hydrothermal fluids helped to generate oil, which migrated upwards or downwards from the source rock and filled intrusive veins, before solidifying to bitumen, by loss of volatile elements. This unconventional hydrocarbon system may have significant implications for regional exploration in the foothills of the Andes.

Openhole, Multistage Fracturing Holds Big Potential in Argentina

Technology Update Almost a century after its first oil discovery, Argentina is making headlines again through reports of the potential of the Vaca Muerta Shale in the Neuquén Basin—the most prolific basin in Argentina (Fig. 1). The existence of Vaca Muerta, which means “dead cow,” has been known for years, but the formation received little attention until the development of shale plays in North America. Vaca Muerta is virtually a virgin play with only a few operators involved. Yet with Argentina’s need to increase production and reduce dependence on foreign oil and gas, change is clearly in the air. Expanding Reserves and Production YPF has reported reserves and resources in the Vaca Muerta formation to be an estimated 22.8 billion BOE (YPF 2012). Encouraged by the estimate, YPF and several other Argentinean operators are continuing exploration activity to define the extent and productivity of the Vaca Muerta, particularly to identify the oil, wet gas, and dry gas areas. Early results suggest that Argentina has an opportunity to replicate the unconventional resource revolution of the United States and eventually meet domestic oil and gas demand through internal production. Argentina has the potential to increase oil and gas production by 50% in 10 years, which would reverse the negative trend that turned the country into a net importer in recent years. Yet this potential does not come easily, as preliminary estimates indicate the need for more than 1,000 wells to be drilled as a first step and 40 additional rigs to accomplish the goal. Besides the investment challenge that the Vaca Muerta now faces, there is an immediate challenge that needs to be dealt with: What is the best way to produce Vaca Muerta? Maximizing Production in Shale, Other Tight Plays In North America, the production of oil and gas from shale has increased greatly since 2007, with the development of several key plays such as the Bakken in North Dakota, the Barnett and Eagle Ford in Texas, and the Marcellus in the eastern United States, which have helped to reverse the declining production of the past few decades. The US and Canadian oil and gas industries were prepared for shale development. While these plays were not new to them, the use of new, unconventional exploitation technologies has been critical to success. In particular, as several studies have proved and is widely known in the industry, the challenge in these shale plays is connecting productive channels and creating fractures that will allow proper fluid movement and endure through the production cycles.