“Vaca Muerta,” once a little-known term outside of Argentina, is now part of nearly everyone’s vocabulary across Latin America and much of North America.
The enormous unconventional resource potential of the Vaca Muerta in Neuquén Province emerged only in the past few years. Until YPF’s Vaca Muerta discovery wells in 2010, the Neuquén Basin was considered over-produced and nearly depleted. Now, the Vaca Muerta is understood industry wide to reference the leading shale play in Latin America.
In fact, industry experts at the AAPG GTW Argentina held in Buenos Aires in early December favorably compared the Vaca Muerta with U.S. shale plays like the Haynesville, Utica and Eagle Ford. Cautious optimism pervaded the remarkably open discussion among 150 workshop participants from nine countries in Latin America and North America.
Geoscience professionals from 54 companies considered the following question: With proper development of the Vaca Muerta formation, could Latin American success rival the North American unconventional resource boom?
According to a February 2012 audit report by Ryder Scott for Repsol-YPF, gross prospective resources of 21.167 billion barrels of oil equivalent from the Vaca Muerta shale oil and shale gas were assessed in an area of 8,071 square kilometers. Of that, 12.351 billion barrels of oil equivalent are net YPF.
Beginning in 2007, YPF began looking for other energy sources. By looking at legacy data from over 130 wells with tests or cores in the Vaca Muerta, YPF found data indicating an underbalanced system and positive initial production rates.
Motivated by this promising data, the company drilled and completed a shale gas discovery in July 2010 in the Loma La Lata area. Shortly thereafter in November 2010, a shale oil discovery was made in the Loma Compana area of Neuquén Province.
Then between 2010 and 2011, according to YPF sources, YPF drilled or worked over a total of 12 wells in the Loma La Lata-Loma Campana area blocks in order to delineate the Vaca Muerta play. The company tested the play in 2011 by drilling the first horizontal well.
All the wells tested oil and gas from the Vaca Muerta marls in an area of more than 300 square kilometers.
As of last October, YPF and 10 partner companies completed 31 Vaca Muerta producing wells, seven of which produce gas. Nearly 20 more await completion or re-entry. Gas production rates exceed 7,000 kscf/d and oil production rates exceed 3,500 bbl/d.
Many of the reservoir characteristics used by North American operators to define the “sweet spot” for optimum hydrocarbon generation and producibility are known. GTW participants discussed and debated at the end of each session, then reported out the best ideas from their table. Operators and service companies with North American experience, like Shell, ExxonMobil, Weatherford and Schlumberger, shared key factors for identifying sweet spots.
That included:
- The right paleogeography – the Neuquén embayment is Cretaceous in age (Tithonian, 150 mya).
- The right depositional environment – resulting in Type I Kerogen, carbonate dominated, low clastic input.
- The right rock type and geomechanical properties – Silica/carbonate-rich, brittle rocks result in greater natural fractures and more easily induced fractures.
- The right petrophysics – high gamma ray, high resistivity, low density, slow compressional velocity, TOC cutoff 2 percent.
- Thick and laterally extensive – over 400 meters thick, basin wide.
Session chair Jeff Ottmann, an AAPG member, offered a straightforward, practical definition of “sweet spot” as the presence of producible hydrocarbons.
“In areas where clay content is reduced, the rock is brittle,” Ottmann pointed out. “In many of these source rocks, most if not all porosity is filled with hydrocarbons.”
Data, Data, Data
Throughout the GTW, a common theme was repeated: Data acquisition will be essential to understand the Vaca Muerta reservoir; data sharing will escalate the learning curve; regional data integration contributes to finding the sweet spot trends, which reduces risk, saving time and money.
Among the GTW Argentina presenters was professor Héctor A. Leanza, Departamento de Geología, Museo Argentino de Ciencias Naturales – CONICET. Revered among Argentina geoscientists, Leanza is known locally for mapping the Vaca Muerta from top to bottom. His expertise is so valued that he frequently is invited to accompany industry for its fieldwork.
“The thickness and variability of the Vaca Muerta, both vertically and laterally, calls for an interdisciplinary survey of the region,” Leanza said.
There was consensus among the workshop attendees that comprehensive data from the Neuquén Basin existed among the industry players. The missing piece, acknowledged by operators, service companies and academia alike, was regional data sharing and integration through joint ventures and partnerships.
Industry Consortia
Rarely do students attend GTWs – they are designed for seasoned professionals and academics, which explains why AAPG member Henry Kernan was the lone student attending GTW Argentina.
But the justification for Kernan’s presence at the workshop was indisputable. A master’s student at Colorado School of Mines and former ExxonMobil geoscientist, Kernan had carefully planned his trip to Argentina. Following participation in GTW Argentina, his itinerary included seven to 10 days of fieldwork along the western portion of the Neuquén Basin.
Focusing on the outer ramp of the Vaca Muerta, Kernan would soon conduct mapping and gather samples alongside a team from Pluspetrol Argentina.
“Following our field work,” Kernan said, “we’ll be conducting source rock analysis with X-ray diffraction and scanning electron microscopy to determine the geomechanical properties and sequence stratigraphy.”
Kernan is a member of the Colorado School of Mines, Vaca Muerta Consortium, and Pluspetrol is the founding member of the Consortium. Pluspetrol is the leading enterprise member, having contributed seismic and well data.
In addition to Pluspetrol, other consortia members include Chevron, Halliburton, Shell and Weatherford.
The idea of an industry-university consortium is a proven concept with past AAPG president and Honorary Member Steve Sonnenberg, who spearheads two other research consortia focused on the Bakken and Niobrara.
“The idea for the consortium occurred as a result of Carlos Portela and me visiting about my other research consortiums,” Sonnenberg said. “These research projects are focused on what we consider to be important (world class) petroleum systems.
“Portela and I decided the Vaca Muerta would be a potential consortium project, and thus it started,” he added.
It turns out that Portela, now corporate operations vice president for Pluspetrol Argentina, holds a master’s in petroleum engineering from Colorado School of Mines.
The Vaca Muerta Consortium will address many issues companies want to analyze but may not have the time to do themselves, including regional source rock characterization, regional stratigraphy, the role of natural fractures in production, the geomechanics of the unit, 3-D seismic attribute analysis and petrophysical analysis.
“This consortium is different from other consortiums because it is all about student- based research supervised by principal investigators,” Sonnenberg said, “with the areas of research suggested by participating companies.”
The Unconventional Learning Curve
In North America, lessons learned from one unconventional play often are applied to the next play.
“The learning curve in the Marcellus took 17 years, (and) in the Eagle Ford it was two years,” said session chair Ottmann, who is technical team lead of Argentina operations for ExxonMobil.
“In Argentina, the question is learning about the efficient development of unconventional resources,” said fellow session chair Güimar Vaca Coca, managing director, Americas Petrogas. “We need an honest data exchange to shorten the learning curve.”
GTW Argentina presenters and participants alike were eager to share ideas and expertise during the workshop. By the end, it seemed that everyone recognized they had more to gain and less to lose by pooling their experiences, lessons learned and even their data.